AN ABSTRACT OF THE THESIS OF

John M. Marcek

in Animal Science

for the degree of Master of Science

presented on September 26, 1983

Title: THE EFFECT OF PHOTOPERIOD ON MILK PRODUCTION AND

PROLACTIN IN HOLSTEIN DAIRY COWS

Abstract approved:Redacted for Privacy

Lloyd V. Swanson

Fourteen multiparous Holstein cows were paired by stage of

lactation and previous years milk yield and 14 Holstein first-calf

heifers were paired by stage of lactation. One member of each pair

was assigned to a 24L:OD or a 18L:6D photoperiod for 16 wk during

winter 1981 (Experiment 1). A similar experiment comparing natural

photoperiod (9-12 h light/day) and 18L:6D was conducted for 9 wk

during winter 1982 (Experiment 2) in which 24 Holstein cows and 22

Holstein first-calf heifers were paired and assigned to groups as

in the first experiment. Animals were housed in a free stall barn

open on 2 sides. High pressure sodium vapor lamps provided light

intensity at cow eye level of 254 26 lux during the day and 132 9 lux

at night. In Experiment 1, concentration of serum prolactin (PRL)

in response to thyrotropin releasing hormone (TRH)(33 ig/100 kg BW)

was measured in 5 animals from each group. Prolactin response to

TRH or saline was tested in 10 animals in each group in Experiment 2.

Photoperiod had no effect on 4% fat corrected milk (FCM) in either

age group in Experiment 1 although cows in the 18L:6D group averaged

2% higher monthly persistency in 4% FCM over the 12 wk that milk

composition was monitered. Cows in the 18L:6D group averaged 5%

higher monthly persistency in 4% FCM in Experiment 2 as compared to

cows exposed to a natural photoperiod. Persistency in heifers was

unaffected by photoperiod in this experiment. Basal concentration of

serum PRL was not affected by either age or photoperiod in Experiment

1 (21.3±3.3 ng/ml). Peak concentration of serum PRL after TRH

injection was not affected by photoperiod in the heifer group but

cows exposed to 18L:6D had significantly higher concentrations of

serum PRL after TRH injection than cows exposed to 24L:OD (560±133

vs. 229±54 ng/ml). Basal concentration of serum PRL in Experiment 2

was similar in TRH- and saline-injected animals (26.3±3.1 ng/ml)

but was lower in cows than in heifers (17.1±2.0 vs. 35.5±5.0 ng/ml).

Saline injection did not elicit a PRL increase nor were there any

differences in concentration of serum PRL due to either photoperiod

or age after TRH stimulation in Experiment 2. Weight gain of cows

did not differ due to photoperiod in Experiment 1 although heifers

exposed to 24L:OD gained more weight than those exposed to 18L:6D.

Cows in Experiment 2 gained significantly more weight when exposed

to 18L:6D. No difference in weight gain due to photoperiod was

observed for heifers in Experiment 2. We conclude that milk yield

in mature cows can be increased by using supplemental lighting during

winter months when compared to natural photoperiod. No differences

between 18L:6D and 24L:OD were observed. Prolactin does not appear

to be involved in the mechanism of action of photoperiods stimulation

of milk yield. Cost analysis of the above data reveal a $16.06 return

on each dollar invested for supplemental lighting. The additional

income realized through supplemental lighting may allow the

dairyman to reduce herd size and operating costs.

The Effect Of Photoperiod On Milk ProductionAnd Prolactin In Holstein Dairy Cows

by

John M. Marcek

A THESIS

submitted to

Oregon State University

in partial fulfillment ofthe requirements for the

degree ofMaster of Science

Completed September 26, 1983

Commencement June 1984

APPROVED:

Redacted for PrivacyProfessor offAnimal Science in charge of major

Redacted for Privacy

Head of Department of Animal Science

Redacted for Privacy

Dean of Gradi4te School

Date thesis is presented September 26, 1983

Typed by Lisa M. Harris for John M. Marcek

ACIZiOWLEDGEHENT

I would like to thank Dr. Lloyd V. Swanson, my advisor and close

friend for his inspirations and insights throughout the course of my

work. From the intricacies of the laboratory to the unclimbable peak

of Mt. Washington he provided encouragement and enthusiasm to help me

complete my tasks. I would also like to thank the Oregon Agricultural

Experiment Station and the Oregon Dairymans Association who provided

the funds necessary for me to pursue my studies. Special thanks are

also extended to Dr. Fredrick Stormshak whose support, humor, and love

of science served as an inspiration to me. My fellow graduate students

also deserve many thanks for their neverending support, understanding,

and encouragement.

I would also like to express my appreciation to both my parents

and my in-laws for their continued love and encouragement during the

past two years. My dog Harry, who always had time to listen, also

deserves special mention.

Finally, I wish to express my deepest appreciation to my wife

Tricia, whose continued love and support helped me get through the

hard times, and made the good times more enjoyable.

TABLE OF CONTENTS

Chapter 1 Introduction 1

Chapter 2 Review of Literature 4

Chapter 3 Effect of Photoperiod on Milk Production andProlactin in Holstein Dairy Cows 19Abstract 20Introduction 22Materials and Methods 24Results and Discussion 27References 47

Chapter 4 Conclusion 49

Bibliography 52

Appendix 59

LIST OF FIGURES

Figure Page

1 Mean weekly milk yields for heifers in Experiment 1exposed to two photoperiods (18L:6L and 24L:OD) . . . . 37

2 Mean weekly four percent fat corrected milk (4% FCM)for heifers in Experiment 2 exposed to two photoperiods(18L:6D and natural) 39

3 Mean weekly milk yield for cows in Experiment 1 exposedto two photoperiods (18L:6D and 24L:OD) 41

4 Mean weekly four percent fat corrected milk (4% FCM)for cows in Experiment 2 exposed to two photoperiods(18L:6D and natural) 43

5 Mean weekly kilograms milkfat per day for cows inExperiment 2 exposed to two photoperiods (18L:6D andnatural) 45

Appendix Figure 1Mean weekly kilograms feed consumed (as fed) per day forcows exposed to two photoperiods (18L:6D and 24L:OD) . . 65

Appendix Figure 2Mean weekly kilograms feed consumed (as fed) per day forheifers exposed to two photoperiods (18L:6D andnatural) 67

Table

1 Serum prolactinheifers at restleasing hormoneExperiment 1

2 Serum prolactinheifers at restleasing hormoneExperiment 2

LIST OF TABLES

concentration (ng/ml) in cows and(basal) and after thyrotropin re-(TRH) challenge (33Pg/100kg BW)

concentration (ng/m1) in cows and(basal) and after thyrotropin re-(TRH) challenge (33pg/100kg BW)

3 Mean monthly body weight (kg) of cows and heifersexposed to various photoperiods

Appendix Table 1Mean weekly kilograms feed consumed (as fed) per dayfor cows and heifers in Experiments 1 and 2

Appendix Table 2Accuracy of KaMar Heatmount Detectors in cows andheifers in Experiment 1

Page

34

35

36

62

63

The Effect of Photoperiod on Milk Productionand Prolactin in Holstein Dairy Cows

INTRODUCTION

Photoperiod or length of daily exposure to light, natural or

artificial, has recently been studied as one of the important

biological cues by which physiological changes are controlled in

animals. Animals in the wild respond to changes in photoperiod in

several ways. Hibernation and migration are examples of these

responses although photoperiod is not the only environmental cue

involved in these phenomena. The greatest potential application

of these physiological changes for man's benefit is in farm animals.

The use of gradually changing photoperiod, constant long or short

photoperiod, and intermittent photoperiod have long been known to

poultrymen. By manipulating photoperiod, growth, maturation rate,

and other traits can be enhanced to increase production in chickens.

Intermittent lighting provides a double savings by stimulating

physiologic changes in chickens as well as decreasing the usage

of electricity.

Photoperiod is also an important environmental cue in the

regulation of sexual activity in seasonal breeding animals. There

are two types of seasonal breeders, those that breed as daylength

decreases (short day breeders, such as sheep) and those that breed

as daylength increases (long day breeders, such as the horse). The

seasonality of breeding is important for survival of the young.

Sheep, which normally breed in autumn when photoperiod is decreasing,

will lamb in spring when temperatures are warmer and grass is

2

becoming more abundant for the growing lambs. Horses have a much

longer gestation period. They breed in spring as daylength is

increasing and will foal the following spring when pasture is lush

and abundant. Horses also provide an example of manipulation

of breeding season through the use of artificial photoperiod. Most

horse registry associations consider January 1 to be the beginning

of a new registration year, making it advantageous to the breeder

to have his horses foal as close to (but after) January 1 as possible.

To do this the normal breeding season must be advanced from April

or May to February or March. Enclosed photoperiod-controlled barns

have made this possible.

The effects of photoperiod on reproduction are many. This

thesis deals only with production traits of farm animals. Recent

experiments in sheep have shown that by manipulating photoperiod,

growth rate may be increased, possibly decreasing the length of

time necessary to produce market lambs. Cattle also respond to

increased photoperiod with increased growth rates. Reports of

photoperiods effects on growth rate in swine are not yet conclusive.

In the past five years, evidence has been presented which

indicates that supplemental lighting will stimulate lactation in

the dairy cow. Increased length of photoperiod is a factor easily

controlled in our modern dairies. The objective of this thesis is

to investigate the effects of supplemental lighting on milk pro-

duction in dairy cows during winter when natural photoperiod is

short. The economic gains which may be realized by the dairyman

through the manipulation of photoperiod are great, especially in

3

the large freestall barns typical of Oregon. Most cows in these

barns are subjected to little or no supplemental light during

winter months when daily photoperiods range from 9 to 12 hours of

light per day. Although night lights are generally used, they

may provide insufficient intensity to be stimulatory to milk

production. In addition, the possible involvement of prolactin

(PRL), a hormone which is known to be influenced by photoperiod

and is essential for lactation in the bovine, will be investigated.

4

REVIEW OF THE LITERATURE

Chickens

The influence of photoperiod on growth and egg production in

chickens has been known for many years. Photoperiod influences

growth rate in chickens by changing feed intake patterns. Siegel et

al. (1963) observed that chicks exposed to 6 hours of light: 18

hours of darkness per day (6L:18D) grew faster than those exposed

to 14L:10D photoperiods. Feed intake data showed that chicks

exposed to shorter photoperiod learned to eat during the dark

portion of the cycle, whereas those exposed to a longer photoperiod

fasted most of the night (Morris, 1967a). Total feed intake over

the 24 hour period did not differ between the two groups. In

contrast, Squibb and Collier (1979) have observed that feed intake

occurs uniformly when chicks are exposed to continuous light. The

constant flow of nutrients to the tissues can then be used more

efficiently in the growing bird. Early experimenters observed that

chicks can be reared in constant darkness without any reduction in

body weight (Cherry and Bardwick, 1962; King, 1962). Later research,

however, indicates that continuous light has a distinct advantage

over light-dark sequences or constant darkness (Van Tienhoven and

Ostrander, 1976).

Intermittent lighting has been used by commercial broiler

producers mostly as an energy saving mechanism. Barott and Pringle

(1951) observed a stimulatory effect of intermittent lighting when

compared to 12L:12D; however continuous light still maintained the

5

highest weight gains (Beane et al., 1962). Generally, any system

of lighting that does not impose periods of rest, which decreases

feed intake, will increase growth rate. This is done most easily

with continuous light or continuous dark (Morris, 1967a).

Light intensity is an important factor regulating growth rate.

Cherry and Bardwick (1962) and Skoglund and Palmer (1962) reported

decreased weight gains associated with higher intensity lighting.

Intensities in these experiments ranged from 0.4 to 1200 lux. In a

commercial flock where lighting sufficient for feeding, maintaining

equipment and observation of birds must be maintained, management

is the key factor to determine the lower limit of light intensity

to be used. Cherry and Bardwick (1962) observed no difference in

growth rate attributable to red or white light at two intensities.

Green light (545 nm) also was effective as a growth stimulant

(Menaker, 1971).

Altered photoperiod also can stimulate or retard age at sexual

maturity. Data from several experiments suggests that chicks respond

to varying lengths of photoperiod in a curvilinear fashion with the

earliest sexual maturation occurring in chicks exposed to 10 hours

of light per day (Morris, 1967a). The influence of photoperiod on

sexual maturation is most evident when a changing photoperiod is

used. Chicks reared on increasing or decreasing photoperiods will

respond with an increased or decreased rate of maturation, respectively

(Morris, 1979; Tucker and Ringer, 1982). The important factor in

this instance is not the length of day but the rate of change

(Morris and Fox, 1958). Chicks hatched in winter and early spring will

6

mature precociously if exposed to the slowly increasing natural

photoperiods seen in higher latitudes during this time of year.

Although it may appear advantageous for birds to begin laying at

a younger age, smaller eggs, higher incidence of uterine prolapse,

increased mortality, and overall decreased egg production have been

reported (Morris and Fox, 1958; Morris 1967a, 1979). Delaying

maturation by supplying extra light or decreasing daily photoperiod

will increase the weight of eggs subsequently laid (Morris and

Fox, 1958; Tucker and Ringer, 1982), as well as increase the number

of eggs laid in the first year of production (Morris and Fox, 1959).

By manipulating photoperiod, age at maturity and subsequent maximum

egg yield can be obtained. Best yields have been obtained by

choosing a photoperiod designed to maximize ovulation rate (Morris,

1979). Gradually increasing the photoperiod as chicks approach

maturity (i.e. 18-20 weeks of age) results in increased egg production.

Increasing the photoperiod at this age has more profound effects

than if increased at an earlier age because the birds are more

sensitive to photoperiod changes as they approach maturity (Morris,

1967a). The intensity of light does not seem to be a major factor

in determining age at initiation of egg laying as pullets have

been reared successfully in both high and low intensity light

(Morris, 1967b).

Egg production is maximized by exposing birds to increasing

photoperiods to a maximum of 16 hours of light per day; further

increases do not result in increased egg production (Morris, 1967a;

Tucker and Ringer, 1982). Pullets therefore must be raised on short

7

photoperiods so that increases in daily photoperiod may be

implemented. Constant photoperiods of 6 to 10 hours of light per

day stimulate egg production compared to shorter photoperiods

(Morris, 1979).

Intermittent lighting is a topic of interest to many producers.

Experiments by Van Tienhoven and Ostrander (1976) have shown that

birds exposed to 2L:10D:2L:10D or 2L:12D:2L:8D maintain equal egg

production, egg weight, and feed efficiency when compared to birds

exposed to 14L:lOD. The savings of 10 hours of electricity per

day without reduction in production would have significant impact

on the poultry industry. A minimum intensity of 2 to 10 lux is

required to maintain maximum egg production in chickens (Morris and

Owen, 1966).

Ahemeral or non 24 hour light cycles have been used in an

attempt to increase egg production. Success in these ventures

depends on breeding a chicken which is productive on a light cycle

shorter than 24 hours. To date, however, selection for this

trait has not been successful (Foster, 1972; Tucker and Ringer,

1982). Cycles longer than 24 hours have been used to increase egg

weight and shell thickness (Morris, 1978). Long photoperiod cycles

will reduce overall yield but may be useful for commercial producers

if market conditions for production of large eggs are favorable.

Sheep

The effects of photoperiod on production traits in sheep have

been studied extensively. Long days increase growth rate in

wethers and ram and ewe lambs (Forbes et al., 1975, 1979;

8

Schanbacher and Crouse, 1980). Forbes et al. (1979, 1981) observed

that 16L:8D tended to stimulate deposition of muscle in lambs fed

ad libitum or restricted diets. Pelt weights and gut fill of

sheep also increased with longer photoperiods. Lambs exposed to

16 hours light also increased feed intake on both diets in this

experiment. The physiological mechanism by which photoperiod

increases feed intake is unclear. In these studies, however,

metabolic weight increased in animals exposed to 16L and the increase

in feed consumption may have been necessary to maintain the

increased maintenance requirements.

Lambs do not increase body weight due solely to an increase

in feed intake as was observed in chickens (Morris, 1967a). Feed

efficiency was also increased by use of long days (Forbes et al.,

1975, 1979; Schanbacher and Crouse, 1980, 1981). Hackett and Hillers

(1979) did not observe increases in growth rate, feed efficiency,

or carcass composition when lambs were exposed to longer photoperiods.

In this experiment lambs were exposed to night lighting in open

range conditions. The environmental differences between the studies

(open range vs. confinement rearing) may account for the dis-

crepancies observed. Ambient temperature is also important in

regulating feed intake and interactions between photoperiod and

temperature have been observed (Schanbacher et al., 1982). Lambs

exposed to a longer photoperiod at higher temperatures did not

decrease feed intake as much as lambs exposed to a short photoperiod.

Constant photoperiod is not essential for the increased growth

rate of longer photoperiod to be observed. Intermittent photo-

9

periods of 7L:9D:1L:7D were as effective as 16L:8D in growth

stimulation (Schanbacher and Crouse, 1981). This supports the

hypothesis that physiological responses will occur if light occurs

coincident with endogenous daily rhythms in photosensitivity

(Bunning, 1960). This phenomenon will be described in a later

section of this review.

Cattle

Similar to sheep, increased weight gains due to increased

photoperiod have been observed in cattle. Average daily gains of

Holstein heifers in Michigan increased by 10 to 15% when exposed

to longer photoperiods during winter months. Heifers exposed to

continuous photoperiod did not increase weight gains in comparison

to heifers exposed to natural photoperiod (Peters et al., 1978,

1980). Several weeks of exposure to increased photoperiod were

required before body growth increased. Like sheep, heifers ate

more and were more efficient in converting feed to gain when exposed

to longer photoperiods (Peters et al., 1980). Even when intake is

restricted, animals exposed to 16L gained weight faster (Petitclerc

et al., 1981). Similar to results in sheep, 16L caused an increase

in protein deposition compared to 8L (Tucker and Ringer, 1982).

Zinn et al. (1983) observed no difference in average daily gain or

feed intake in prepubertal heifers due to photoperiod; however,

postpubertal heifers grew faster when exposed to a shorter photoperiod.

Postpubertal heifers exposed to 16L had significantly higher feed

intake and carcass protein percentage whereas heifers exposed to

8L had significantly higher carcass fat percentage. The increase

10

in weight gain observed in postpubertal heifers may have been due

to overfeeding as was evidenced by a 1.24 kg average daily gain in

heifers exposed to 8L. Increased photoperiod in this experiment

increased feed intake but did not consistently affect weight gain.

Longer photoperiod may stimulate protein deposition. Animals

exposed to shorter photoperiods did not achieve the same rate of

protein deposition and excess energy intake may have been diverted

into body fat (Tucker, personal communication).

Growth rate was not increased when steers and bulls up to

98 days of age were subjected to 16L (Roche and Boland, 1980;

Tucker, personal communication). However, Tucker (personal

communication) observed a 9% increase in body weight in older

bulls exposed to 16L. A different mechanism of action, possibly

involving the gonads, may be responsible for increased weight

gain in cattle than in sheep. Sheep are short day breeders and

the gonads are most active during periods of decreasing photoperiod.

Longer photoperiods inhibit gonadal development and secretion.

Serum testosterone concentrations were lower in rams exposed to

16L compared to rams exposed to 8L at 22 weeks of age (Schanbacher

and Crouse, 1980). Cattle are not seasonal breeders and photoperiod

has no effect on gonadal development. Serum androgen concentrations

increased at a faster rate as photoperiod increased in cattle

(Tucker, personal communication).

Swine

The stimulation of growth by longer photoperiods may be limited

to ruminants and poultry. In several recent studies with swine, no

11

differences in growth rate or feed efficiency in boars, barrows,

or gilts were observed (Berger et al., 1980; Mahone et al., 1979;

Ntunde et al., 1979). Puberty occurred at an earlier age in young

male pigs exposed to increasing or decreasing photoperiods (Berger

et al., 1980); however, the effect of photoperiod on puberty in

gilts is not known. Ntunde et al. (1979) has found that gilts

exposed to very short photoperiods of 1.5L had delayed puberty

whereas 18L did not stimulate puberty when compared to 9-11L.

Lactation

Milk yield is another economically important trait affected by

photoperiod. Cows in Michigan increased milk yield 6 to 10% without

affecting milk composition when given supplemental lighting during

winter (Peters et al., 1978, 1981). The effect occurred in both

early and late lactation. Dry matter intake increased in cows

receiving supplemental lighting which may have been responsible

for the increased milk yield (Peters et al., 1981). Results from

experiments investigating the effect of photoperiod on lactation

in swine are inconsistent. Mabry et al. (1982) demonstrated an

increase in milk yield and litter weight at weaning in sows exposed

to 16L whereas Greenberg and Mahone (1982) failed to observe an

effect of photoperiod on milk yield. Photoperiod did, however,

have a stimulatory effect on litter weight gain in mice (Sorenson

and Hacker, 1979).

Pineal and Photoperiod

Research has been conducted to investigate the effects of the

12

pineal gland and its products on growth and milk secretion in

laboratory animals. Short photoperiods or blinding are considered

to stimulate secretion of pineal products while long photoperiods

are inhibitory (Reiter, 1977). Blind anosmic rats, in which the

inhibitory effects of the pineal on the neuroendocrine axis appear

to be maximal, grew at a slower rate than intact animals (Reiter,

1974). The effect of the pineal on feed consumption and feed

efficiency must be considered, however, before these results may

be fully interpreted. Neither mammary development (Mishkinsky et al.,

1966) nor lactation (Nir et al., 1968) were affected by

pinealectomy in rats maintained on 12L:12D photoperiods. Mizuno

and Sensui (1970) also observed no effect of pinealectomy on

litter weights in rats exposed to 14L:10D on day 16 postpartum.

The validity of these experiments has been questioned, however,

by Reiter (1977) who suggests that animals exposed to more than 12

hours of light per day are "physiologically pinealectomized". The

effect of the pineal on lactation in rats, therefore, is subject to

further interpretation.

Sorenson and Hacker (1979) recently studied the effects of

purified bovine pineal extract and light duration on lactation in

mice. Litter weights of mice exposed to 16L were increased as

compared to controls (8L). If photoperiod influences lactation

through its effects on tht.. pineal an interaction between light

duration and administration of pineal extracts would have been

expected. The lack of interaction between photoperiod and pineal

products observed in this experiment may indicate that the pineal

13

is not an important part of the control mechanism and that some

other light sensitive stie may be responsible for increases in milk

yield due to photoperiod.

The administration of pineal extracts as well as the pineal

indoles, serotonin and melatonin, lowered the milk yield curve in

rabbits (Shani et al., 1971); however, Mizuno and Sensui (1970)

found no inhibitory effect of melatonin on litter weight gain in

rats. Again, long photoperiods were used and animals may have been

physiologically pinealectomized. Serotonin has an inhibitory

effect on oxytocin release in response to suckling (Mizuno et al.,

1967) thus suppressing milk yield. In another study, Mizuno and

Sensui (1970) did not observe an effect of pinealectomy or melatonin

administration on the amount of residual milk in rats. Conclusions

on the effect of the pineal gland on milk ejection and lactation

await further investigation.

Pineal extracts have been evaluated for their effects on

the lactogenic hormone PRL. The primary site of action of the

pineal is considered to be the brain (Reiter, 1973). Pineal products

may also act either at the hypothalamo-hypophyseal axis or directly

on the anterior pituitary. Bovine pineal extracts both increased

and decreased PRL secretion from rat hemipituitaries cultured

in vitro (Blask et al., 1976). Similarly, in vivo administration of

bovine pineal extracts elevated (Blask et al., 1976) and suppressed

(Ebels and Benson, 1978) plasma PRL levels in rats. Recent

experiments in blind anosmic rats indicate that the pineal inhibits

PRL synthesis, storage, and release (Leadem and Blask, 1982).

14

Prolactin and Photoperiod

The effects of PRL in mammals are many. Specific effects

of interest in this review are growth and lactation, two traits

also affected by photoperiod.

Prolactin is anabolic in some systems (Nicoll, 1980). Growth

was depressed in sheep immunized against PRL (Ohlson et al.,

1981). But treatment with ergot alkaloids, which also decrease

PRL levels substantially, did not affect growth (Ravault et al.,

1977). Animals in this experiment were exposed to natural photo-

periods during seasons of both increasing and decreasing photoperiods.

The effects of suppression of PRL by ergot alkaloids on growth

of animals exposed to constant long or short photoperiods has not

been studied.

The pineal gland is also important. Pinealectomy inhibits

normal fluctations in blood PRL concentrations in response to

photoperiod (Brown and Forbes, 1980); pinealectomized lambs did

not grow faster when exposed to longer photoperiods.

Prolactin affects milk production by stimulating several key

biochemical processes during lactogenesis in cattle (Akers et al.,

1981). In addition, PRL is necessary for the maintenance of

lactation in the bovine although it is not thought to be a limit-

ing factor (Tucker, 1979).

Serum concentrations of PRL fluctuate seasonally in cattle

(Bourne and Tucker, 1975), sheep (Pelletier, 1973) and goats

(Hart, 1975). Length of photoperiod is positively correlated

with serum PRL concentrations in bulls (Leining et al., 1979).

15

Serum PRL concentrations change more quickly in response to

decreasing photoperiod than to increasing photoperiod (Bourne and

Tucker, 1975). Abrupt increases in photoperiod from 8 hours of

light to 16 to 20 hours of light per day increased PRL concen-

tration after one week and maximal PRL concentrations were

attained at 9 weeks (Leining et al., 1979). Continuous light

resulted in decreased PRL levels similar to that observed under a

natural photoperiod. Experiments using gradual and abrupt changes

in photoperiod have yielded similar results in sheep (Pelletier,

1973; Ravault and Ortavant, 1977). Photoperiods of 15L did not,

however, increase PRL levels in swine when compared to natural

photoperiods of 8L (Hoagland et al., 1981).

Components of light also have been studied in relation to

PRL release. Most experiments studying the effects of photo-

period on PRL in the bovine have been conducted using cool

white fluorescent lights with high intensity (e.g. 600-800 lux)

(Bourne and Tucker, 1975; Leining et al., 1979; Peters et al.,

1981). The threshold of light intensity necessary to elicit

PRL release remains to be determined. A longer photoperiod

(16 hours) utilizing high intensity fluorescent lighting (200 to

300 lux) elicited increased PRL secretion as compared to a

shorter photoperiod (9 to 11 hours) utilizing low intensity indirect

natural light (35 to 40 lux)(Peters and Tucker, 1978). Various

wavelengths of light studied have not been more or less effective

than white light in eliciting PRL release in response to photo-

period (Leining et al., 1979).

16

Prolactin levels are affected by other environmental conditions.

Increased ambient temperature will increase PRL concentration

in cows. Peters and Tucker (1978) observed wide fluctuations in

serum PRL in heifers exposed to 16L:8D. Increases and decreases

in PRL concentration were syndhronized with changes in ambient

temperature. Tucker and Wettemann (1976) observed lower

basal PRL levels in heifers exposed to 4.5°C when compared

to 21°C and 32°C. Prolactin response to thyrotropin releasing

hormone (TRH) injection was also decreased in heifers exposed to

21°C when compared to heifers exposed to 32°C and was not evident

in heifers exposed to 4.5°C. Prolactin was not affected by relative

humidity. The PRL response to temperature supersedes any

response to photoperiod. No differences were observed in serum

PRL concentration in heifers exposed to natural, 16L:8D, or

24L:OD when ambient temperature approached 0°C (Peters et al.,

1980). Thus the effect of photoperiod on PRL and its relation-

ship to growth and lactation is questionable. Increased weight

gains in response to 16L:8D persisted throughout winter in Michigan

(Peters et al., 1978, 1980) and milk yields did not decrease during

exposure to cold (Petitclerc et al., 1981).

Stressful stimuli such as pain will elicit increases in PRL

secretion in cattle (Tucker, 1971), but not swine (Hoagland

et al., 1981). Feeding also has been implicated in the release of

PRL in the bovine (McAtee and Trenkle, 1971) and ad libitum

feeding causes increased serum PRL levels in sheep (Forbes

et al., 1975). Interpretation of PRL levels must be made carefully

17

therefore, as many factors contribute to its secretion.

Photosensitivity

Recently, several experiments have tested the theory of

Bunning (1960) that animals measure time from the degree of coin-

cidence of their daily endogenous rhythm and the external photo-

period. Period of uninterrupted light or uninterrupted dark may

be the signals which entrain the cycle of endogenous photosensitivity

(Pittendrigh and Minis, 1964).

Schanbacher and Crouse (1981) exposed ram lambs to short

(8L:16D), long (16L:8D), and split (7L:9D:1L:7D) photoperiods.

Increased weight gains and feed intake were observed in animals

exposed to the long and split photoperiod. Light was proposed to

be the Zeitgeber for feed intake. The exposure to 1 h of light

16 h after dawn was observed to be in the photosensitive phase

and physiologic responses such as increased weight gain and feed

intake occurred, even though the total photoperiod was only 8 h.

Ravault and Ortavant (1977) and Thimonier et al. (1978) used

Bunnings theory in investigating photosensitivity and PRL

secretion in rams. A split photoperiod (7L:9D:1L:7D) again was as

effective as 16L:8D in eliciting increased PRL secretion.

Insertion of the one hour pulse of light at other times of the day

was ineffective in stimulating PRL secretion. A normal diurnal

rhythm of PRL secretion is present in sheep (Ravault and

Ortavant, 1977) with PRL secretion increasing when lights are

turned off. No such endogenous rhythm is present in cattle

18

although a diurnal rhythm of photosensitivity has been observed

(Petitclerc et al., 1983). A 6L:8D:2L:8D photoperiod was as

effective as 16L:8D in increasing PRL secretion in bulls.

a 2 h pulse of light between 14 to 16 and 20 to 22 hours after

dawn increased PRL levels although light at 20 to 22 hours

after dawn was much less effective. Further experimentation with

photosensitivity and its application to production traits is

important to the animal industry. Significant savings, as those

observed in the poultry industry, may be realized through the

manipulation of photoperiod.

Running Head: Photoperiod and Milk Production

EFFECT OF PHOTOPERIOD ON MILK PRODUCTION

AND PROLACTIN IN HOLSTEIN DAIRY COWS'

J.M. Marcek and L.V. Swanson2

Department of Animal Science

Oregon State University

Corvallis, OR 97331

Key Words: Photoperiod, 4% fat corrected milk, Prolactin, TRH

'Technical Paper No.

2Reprint requests.

, Oregon Agr. Exp. Station.

19

20

ABSTRACT

Fourteen multiparous Holstein cows were paired by stage of

lactation and previous years milk yield and 14 Holstein first-

calf heifers were paired by stage of lactation. One member of

each pair was assigned to a 24L:OD or an 18L:6D photoperiod for

16 wk during winter 1981 (Experiment 1). A similar experiment

comparing natural photoperiod (9-12 h light/day) and 18L:6D was

conducted for 9 wk during winter 1982 (Experiment 2) in which 24

Holstein cows and 22 Holstein first-calf heifers were paired and

assigned to groups as in the first experiment. Animals were

housed in a free stall barn open on 2 sides. High pressure sodium

vapor lamps provided light intensity at cow eye level of 254±26 lux

during the day and 132±9 lux at night. In Experiment 1, concen-

tration of serum prolactin in response to thyrotropin releasing

hormone (33 pg/100 kg body weight) was measured in 5 animals from

each group. Prolactin response to thyrotropin releasing hormone

or saline was tested in 10 animals in each group in Experiment 2.

Photoperiod had no effect on 4% fat corrected milk (FCM) in either

age group in Experiment 1 although cows in the 18L:6D group

averaged 2% higher persistenly in 4% fat corrected milk. Cows

in the 18L:6D group were 7% more persistent in 4% fat corrected

milk in Experiment 2 as compared to cows exposed to a natural

photoperiod. Persistency in heifers was unaffected by photo-

period in this experiment. Basal concentration of serum prolactin

was not affected by either age or photoperiod in Experiment 1

(21.3±3.3 ng/ml). Peak concentration of serum prolactin after

21

thyrotropin releasing hormone injection was not affected by

photoperiod in the heifer group, but cows exposed to 18L:6D

had significantly higher concentrations of serum prolactin after

thyrotropin releasing hormone injection than cows exposed to

24L:OD (560±133 vs. 229±54 ng/ml). Basal concentration of serum

prolactin in Experiment 2 was similar in thyrotropin releasing

hormone and saline-injected animals (26.3±3.1 ng/ml) but was lower

in cows than in heifers (17.1±2.0 vs. 35.5±5.0 ng/ml). In

Experiment 2 saline injection did not elicit a prolactin increase,

nor were there any differences in concentration of serum prolactin

after thyrotropin releasing hormone stimulation due to either

photoperiod or age. Weight gain of cows did not differ due to

photoperiod in Experiment 1 although heifers exposed to 24L:OD

gained more weight than those exposed to 18L:6D. Cows in Experiment

2 gained significantly more weight when exposed to 18L:6D. No

difference in weight gain due to photoperiod was observed for heifers

in Experiment 2. We conclude that milk yield in mature cows can

be increased by using supplemental lighting during winter months

when compared to natural photoperiod. No difference in milk yield

between 18L:6D and 24L:OD were observed. Prolactin does not

appear to be involved in the mechanism of action of photoperiods

stimulation of milk yield.

23

18L:6D and 24L:OD. The effect of these photoperiods on con-

centrations of serum PRL at rest and after TRH stimulation also

was studied.

24

MATERIALS AND METHODS

Experiment 1

Fourteen multiparous Holstein cows and 14 Holstein first-

calf heifers were used. Cows were paired according to previous

year's production and days in lactation (38 to 207 days), whereas

heifers were paired according to days in lactation (31 to 197 days).

One member of each pair was assigned randomly to 18L:6D and the

other to a 24L:OD photoperiod. All animals were on a 24L:OD

photoperiod prior to the experiment. Cows were housed in a free

stall barn open on the north and south sides. Treatment groups

were separated from each other by a length of 28 m within the barn.

Mean intensity of light at cow eye level was 2541-26 lux during the

day and 132±9 lux at night. Identical completely mixed rations

consisting of corn silage, alfalfa hay cubes, whole cottonseed,

and a 16% crude protein dairy concentrate were fed once daily to

cows and heifers in their respective treatment groups.

Cows and heifers were assigned to treatment groups in December

1981 and the experiment was conducted for 16 wk through April 1982.

All animals were maintained on a 24L:OD photoperiod before the

beginning of the experiment. Milk yield and milk composition

(fat, protein) were monitored weekly. All animals were weighed

on two consecutive days each month during the experiment.

To determine if photoperiod had an effect on pituitary PRL,

5 animals from each group were selected randomly for a TRH challenge

experiment. Cows were locked in stanchions and feed was removed

2 h prior to the experiment. Blood samples were collected via tail

25

venipuncture at -30, -15, 0, +5, +10, and +15 min relative to

intravenous injection of a standard dose (33 ug/100kg BW) of TRH

(Sigma Chemical Co., St. Louis, Mo.). Samples were allowed to

clot at room temperature, then centrifuged and the serum decanted.

Serum was stored at -20°C until assayed for PRL content by double

antibody radioimmunoassay (5). NIH-P-B3 was used as the reference

standard.

Experiment 2

A similar experiment was conducted beginning November 1982

for 9 wk through January 1983. For 2 months prior to the start

of the experiment, cows at the Oregon State University Dairy

Center were maintained on a natural photoperiod schedule. Twenty-

four Holstein cows and 22 Holstein first-calf heifers were paired

as in the previous experiment. One member of each pair was assigned

at random to a natural photoperiod and the other to an 18L:6D

photoperiod at 10 days postpartum or later. Cows ranged from 10

to 159 days and heifers ranged from 35 to 283 days in lactation

at the beginning of the experiment. Natural photoperiod during

the experimental period ranged from 9 to 11.5 h light per day.

Housing and feeding schedules were consistent with the previous

experiment. Milk yield, milk composition, and cow weight were

monitored as in Experiment 1.

The effect of photoperiod on PRL was studied as in the first

experiment except that 5 saline-injected animals were included

in each group as controls. Blood samples were collected at -30,

-15, 0, +10, +15, and +20 min relative to administration of the

26

standard dose of TRH.

Persistency of milk yield is defined as the percentage of a

current month's yield relative to the previous month's yield.

Statistical analysis of milk yield, milk composition, and cow

weight data was accomplished using split-plot analysis of variance.

Basal concentrations of PRL in serum and differences between basal

levels and peak TRH-induced concentrations of PRL in serum were

analysed by analysis of variance.

27

RESULTS AND DISCUSSION

Milk yield and 4% FCM were not changed due to altered photo-

period in the heifers for Experiments 1 and 2, respectively,

(Figures 1 and 2) perhaps due to the higher persistency normally

observed in heifers (1). Heifers maintained average monthly

persistencies of 98 to 100% in milk yield and 98 to 101% in 4%

FCM during the experiments.

Milk yield (Figure 3) and 4% FCM were not significantly

different in cows exposed to 18L:6D compared to 24L:OD (Experiment 1)

although monthly persistency of milk yield was 2% higher in the

18L:6D group.

A significant photoperiod by week interaction (P<.01) was

observed in 4% FCM when 18L:6D was compared with natural photo-

period (Figure 4), whereas milk yield did not differ (Experiment 2).

Cows exposed to 18L:6D maintained monthly persistencies of 99%

in 4% FCM while those exposed to natural photoperiod averaged 92%.

Cows exposed to 18L:6D had average monthly persistency of 101%

in milk yield whereas those exposed to natural photoperiod averaged

97% persistency. These results are in agreement with Peters et al.,

(9, 10) who observed that cows exposed to longer photoperiods

during winter months responded with an increase in milk yield;

however, in the present experiment the increase in milk yield was

not statistically significant.

In these experiments, 18L:6D increased milk yield in mature

cows in comparison to a natural photoperiod. Continuous lighting

was as effective in maintaining persistency of milk yield as

28

18L:6D, however direct comparisons between the results of Experiments

1 and 2 cannot be made because they were conducted in different

years and animals were maintained on different control photoperiods

prior to beginning the experiments.

Mechanisms by which photoperiod stimulates increased milk

yield are not known. One possibility is the effect of photoperiod

on feed intake. Peters et al. (9) observed an increase in feed

intake when lactating cows are exposed to longer photoperiods.

This would be an economical method to increase milk yield since

additional feed consumed would exceed maintenance requirements

and be available for milk synthesis. Other experiments indicate

that heifers increase feed intake when exposed to longer photo-

periods but not when exposed to continuous lighting (8, 10). In

a concurrent behavioral study during Experiment 1, Tanida et al.

(14) observed no difference in total time spent eating in cows

exposed to either 18L:6D or 24L:OD. Feeding patterns did not

differ from what previously has been observed for cattle exposed

to natural photoperiod who exhibit diurnal rhythms, eating more

during daylight hours and having peaks of eating activity both in

the morning and afternoon (2). In contrast, Zinn et al. (18)

concluded that lights on, lights off, and presentation of fresh

feed increased feeding activity in prepubertal heifers. Heifers

exposed to short photoperiods began eating about 2 h before lights

on, indicating that entrainment to the light cycle had occurred.

Hafez and Bouissou (4) have suggested that feeding behavior responds

to the influence of ambient temperature as well as to other

29

environmental conditions. It is possible that, if animals were

placed in an environmentally controlled chamber, photoperiod

would be the key Zeitgeber for entrainment of feeding behavior.

In natural barn conditions, however, additional factors such as

daily fluctuations in temperature, humidity, presentation of feed,

and milking activity may influence feeding behavior.

The intensity of light used in this experiment was lower than

that used previously (9, 10). Stevenson et al. (13) observed that

milk production increased linearly in sows as intensity of light

increased. The interaction of light intensity and duration may

also be important in the bovine and warrants further examination.

The effect of photoperiod on percent fat and percent protein

in milk was examined. In Experiment 1, milk samples were analysed

during weeks 1 to 12 of the experiment but data from week 1 were

not included in the analysis due to an error in sampling procedure.

Percent milkfat and percent protein were not affected by photo-

period in heifers in Experiment 2 or cows in Experiment 1.

Differences did exist in the other two groups. A significant

photoperiod by week interaction was observed for percent milkfat

(P<.05) and percent protein (P<.01) in heifers in Experiment 1.

Both traits increased at a more rapid rate during weeks 2 to 12 of

the experiment in heifers exposed to 18L:6D. Significant inter-

actions also were observed for percent milkfat (P<.05), kg milkfat

(P<.01), and percent protein (P<.05) in cows in Experiment 2.

Percent milkfat and kg milkfat (Figure 5) decreased at a slower

rate in cows exposed to 18L:6D as compared to cows exposed to

30

natural photoperiod. This contributed to increased persistency

in 4% FCM and to the interaction observed in kg milkfat. Percent

protein, on the other hand, decreased at a faster rate in cows

exposed to 18L:6D.

We believe that the differences in percent milkfat and

percent protein observed in this experiment are not biologically

important because overall yields of milkfat and protein were not

affected. The one instance in which kg milkfat was affected may

have been due to the increase in milk yield observed. Other

researchers reported no difference in percent milkfat in response

to photoperiod (9). Variations in percent milkfat and percent

protein throughout the lactation are normal (12). Both components

decrease during the beginning of lactation, level off, and then

gradually increase in the latter half of lactation. Many other

factors are also responsible for variation in milk composition

including season, age, stage of lactation, pregnancy, mastitis,

feeding and management practices, as well as individual cow

variation (6). Further examination of our data revealed that in-

herent differences between cows may have been responsible for the

differences observed, since cows were not paired on milk composition

traits at the beginning of the experiments.

Data from the PRL experiments in 1981 are presented in Table 1.

No differences in basal PRL concentration due to photoperiod or

age were observed although cows tended to have higher basal PRL

levels (P=.10) than heifers (27±6 vs. 15±2 ng/ml). Peak PRL levels

after TRH injection were significantly higher (P<.05) in cows

31

exposed to 18L:6D as compared to cows exposed to 24L:OD but did

not differ for the heifers. In the 1982 experiment basal PRL

concentration in saline-injected animals did not differ from basal

PRL levels observed for TRH-injected animals; therefore, the data

were pooled for analysis. Peak PRL concentration after saline

injection was not included in the analysis since saline injection

did not elicit an increase in serum PRL. Basal PRL levels in this

experiment did not differ due to photoperiod although serum PRL

concentrations were higher (P<.01) in heifers than in cows

(Table 2). No differences due to photoperiod or age were observed

in PRL concentration after TRH stimulation.

Endogenous hormone secretion has been hypothesized to be one

mechanism by which photoperiod influences milk yield. Several

hormones are involved in lactogenesis and galactopoiesis in the

bovine. These include placental lactogen, PRL, growth hormone,

glucocorticoids, and thyroxine (15). Of these, PRL is the most

responsive to changes in photoperiod. Peters et al. (9) observed

increased basal concentrations of PRL and increased concentrations

of PRL after TRH stimulation in lactating cows exposed to 16L:8D

as compared to cows exposed to 8L:16D. Growth hormone and thyroxine

are not influenced by photoperiod (7, 8, 9). Some evidence that

glucocorticoid concentration is negatively correlated with photo-

period has been reported in some (7) but not all experiments

(8, 9). Vanjonack and Johnson (17) observed that high producing

cows had higher glucocorticoid levels at lower temperatures but

that corticoid levels decreased faster in high producing cows at

32

higher temperatures. Prolactin is positively correlated with

temperature (16) and low temperatures (approximately 0°C) over-

ride any photoperiod-induced increase in PRL concentration (8).

In our experiment no consistent differences in PRL concentration

due to photoperiod were observed. This is contrary to that observed

previously (7, 8, 9) although the milder climate in which the

experiment was conducted and light source (although wavelength

of light has not been observed to affect PRL concentration (7))

may account for these differences. We do not believe temperature

was an important factor as it was consistent (10°C) throughout

the sampling periods. The lower intensity of lighting may have

accounted for the decreased PRL response to photoperiod, although

Peters and Tucker (11) used low intensity lighting (i.e. 300 lux)

and observed an increase in serum PRL concentration in heifers

in response to longer photoperiod. Because of the nonspecific

nature of prolactin release, other factors of which we were not

aware may have produced the significant differences observed.

The inconsistencies observed in serum concentrations of PRL do

not seem to be related to the increases observed in milk yield.

This adds further evidence that prolactin is not a limiting factor

for milk yield in the bovine.

First-calf heifers, but not cows, exposed to 24L:OD gained

weight faster (P<.05) than those exposed to 18L:6D in Experiment 1

(Table 3). There were no differences in heifers in Experiment 2.

Cows in Experiment 2 gained significantly more weight (P<.01) when

exposed to 18L:6D. Peters et al. (9) did not detect differences

33

in weight gain due to photoperiod in lactating cows. We may have

encountered genetic differences or environmental factors such as

competition for bunk space or competition between cows. Diets,

however, were the same for the two heifer and two cow groups.

From these data we conclude that increased photoperiod during

winter months stimulates milk yield in cows but not in first-calf

heifers. Milk yield, however, did not differ in cows or heifers

exposed to continuous lighting as compared to those exposed to

18L:6D. Increased percentages of protein and fat were observed

in some experiments; however, total fat and protein yields did

not differ.

Serum PRL concentration did not increase in response to

photoperiod as had been observed previously. This may have been

due to different climatic conditions or different intensity of

lighting. These data do not indicate that PRL is responsible for

the increase observed in milk production due to photoperiod.

34

Table 1. Serum prolactin concentration (ng/ml) in cows and heifers at rest(basal) and after thyrotropin releasing hormone (TRH) challenge(33 ug/100 kg) Experiment 1.

Basal

TRHStimulateda

24L:OD 18L:6D 24L:OD 18L:6D

Cows 23+6bc 31±11c 229±54d 560±133e

Heifers 17±3c 14±2c 390±65d

390±86d

aData represent peak concentration minus basal concentration

bMean ± SE

c,d,eMeans in rows not sharing a common superscript differ (P<.05)

Table 2. Serum prolactin concentration (ng/ml) in cows and heifers atrest (basal) and after thyrotropin releasing hormone (TRH)challenge (33 ug/100 kg) Experiment 2.

BasalTRH

Stimulateda

Natural Natural

Photoperiod 18L:6D Photoperiod 18L:6D

35

Cows 14±2b 20±3 584±113 620±90

Heifers 41±7 30±7 426±145 616±143

aData represent peak concentration minus basal concentration

bMean ± SE

36

Table 3. Mean monthly body weights (kg) of cows and first-calf heifers exposedto various photoperiods.

Experiment 1

Cows

Month 24L:0Da 18L:6Da

Heifers

24L:ODb

18L:6Dc

1 666±12d

634±20 616±20 587±11

2 672±14 635±19 621±21 583±12

3 673 ±11 639±20 631±22 587±11

Experiment 2

Cows Heifers

Natural Natural

Month Photoperiod 18L:6Db

Photoperiod 18L:6Dc

1 667±22 658±13 631±10 601±6

2 668±20 664±14 642±9 602±7

3 669±20 686±16 659110 629±8

a,b,cPhotoperiod treatments within experiments not sharing a common superscript

differ (P<.05) over time.dMean ± SE

37

FIGURE 1. Mean weekly milk yields for heifers in Experiment 1exposed to two photoperiods (18L:6D and 24L:OD).Straight lines represent regressions computed fromthe data.

35

251

, \

- --4:V --\-- ----III

FIGURE I

24L:OD

I a a a a a I I I

0 2 4 6 8WEEKS

I0 12 14 16

39

FIGURE 2. Mean weekly four percent fat corrected milk (4% FCM)for heifers in Experiment 2 exposed to two photo-periods (18L:6D and natural). Straight lines rep-

resent regressions computed from the data.

30

25

40

Natutol Photoperiod

FIGURE 2

2 4

18L.:61:10

WEEKS6 8

41

FIGURE 3. Mean weekly milk yield for cows in Experiment 1 exposed

to two photoperiods (18L:6D and 24L:OD). Straightlines represent regression lines computed from the data.

N co0

\I

N 41 co

m m c

ox co

0 TT

)

71%

Z17

i

KG

MIL

K/D

AY

ca 0co cs

11

i1

1i

1i

i1

I

-*I

G) C 23 rn cg

1

43

FIGURE 4. Mean weekly 4% FCM for cows in Experiment 2 exposed totwo photoperiods (18L:6D and natural). Straight linesrepresent regressions computed from the data.

40

30

0 2 4WEEKS

6 8

45

FIGURE 5. Mean weekly kilograms milkfat per day for cows inExperiment 2 exposed to two photoperiods (18L:6D andnatural).

1.8

1.6

1.0

0.8

Vi5VGC)--C

-.0-- N

Natural Photoperiod

FIGURE 5

,o--0

I t I t i t t i0 2 4 6 8

WEEKS

47

REFERENCES

1 Campbell, J.R., and R.T. Marshall. 1975. The Science of Pro-viding Milk for Man. pp 249. McGraw-Hill Book Company, New York.

2 Chase, L.E., P.J. Wangsness, and B.R. Baumgardt. 1976. Feed-ing behavior of steers fed a complete mixed ration. J. DairySci. 59:1923.

3 Convey, E.M., H.A. Tucker, V.G. Smith, and J. Zolman. 1973.Bovine prolactin, growth hormone, thyroxine, and corticoidresponse to thyrotropin-releasing hormone. Endocrinology92:471.

4 Hafez, E.S.E., and M.F. Bouissou. 1975. The behaviour ofcattle. In: E.S.E. Hafez (Ed.) The Behavior of Domestic Animals.(3rd Ed). pp 532. Bailliere Trindall, London.

5 Koprowski, J.A., and H.A. Tucker. 1971. Failure of oxytocinto initiate prolactin or LH release in lactating dairy cattle.J. Dairy Sci. 54:1675.

6 Laben, R.L., R. Shanks, P.J. Berger, and A.E. Freeman. 1982.

Factors effecting milk yield and reproductive performance.J. Dairy Sci. 65:1004.

7 Leining, K.B., R.A. Bourne, and H.A. Tucker. 1979. Prolactinresponse to duration and wavelength of light in prepubertalbulls. Endocrinology 104:289.

8 Peters, R.R., L.T. Chapin, R.S. Emery, and H.A. Tucker. 1980.

Growth and hormonal response of heifers to various photoperiods.J. Anim. Sci. 51:1148.

9 Peters, R.R., L.T. Chapin, R.S. Emery, and H.A. Tucker. 1981.

Milk yield, feed intake, prolactin, growth hormone, glucocorti-coid, response of cows to supplemental light. J. Dairy Sci.64:1671.

10 Peters, R.R., L.T. Chapin, K.B. Leining, and H.A. Tucker. 1978.

Supplemental lighting stimulates growth and lactation in cattle.Science 199:911.

11 Peters, R.R., and H.A. Tucker. 1978. Prolactin and growthhormone response to photoperiod in heifers. Endocrinology

103:229.

12 Rook, J.A.F., and R.C. Campling. 1965. Effect of stage oflactation on the yield and composition of cows milk. J. Dairy

Res. 32:45.

48

13 Stevenson, J.S., D.S. Pollmann, D.L. Davis, and J.P. Murphy.1983. Influence of supplemental light on sow performanceduring and after lactation. J. Anim. Sci. 56:1282.

14 Tanida, H., L.V. Swanson, and W.D. Hohenboken. 1983. Arti-ficial photoperiod and behavior in dairy cows. J. Anim. Sci.57:Suppl. 1, 142.

15 Tucker, H.A. 1979. Endocrinology of Lactation. Seminarsin Perinatology 3:199.

16 Tucker, H.A., and R.P. Wettemann. 1976. Effect of ambienttemperature and relative humidity on serum growth hormone andprolactin in heifers. Proc. Soc. Exp. Biol. Med. 151:623.

17 Vanjonack, W.J., and H.D. Johnson. 1975. Effect of heat andmilk yield on bovine plasma glucocorticoid levels. Proc. Soc.Exp. Biol. Med. 148:970.

18 Zinn, S.A., L.T. Chapin, and H.A. Tucker. 1983. Does photo-period and time of feeding affect growth and eating pattern ofheifers? J. Anim. Sci. 57:Suppl. 1, 217.

49

CONCLUSIONS

This and other studies have demonstrated that 16 to 18 h

light per day increase milk yield in mature dairy cows when compared

to natural photoperiod. Cows exposed to continuous lighting in

this experiment did not differ in milk yield from cows exposed to

18 h light. Further study is needed to determine the optimum

photoperiod as well as minimum intensity required for maximum

stimulation of milk yield in the dairy cow. Recent experiments

using split photoperiods in bulls indicate a photosensitive phase

for PRL release in the bovine (Petitclerc et al., 1983). Research

investigating the use of a split photoperiod to stimulate milk

production should also be conducted.

The mechanism by which photoperiod stimulates milk yield is

not understood. Results of this experiment add further evidence

that PRL is not responsible for the increases observed. The effects

of the pineal on PRL and lactation have just begun to be studied.

This endocrine organ may have significant impact on lactation

through products which have not, as yet, been identified. The effects

of photoperiod on other parts of the brain should be examined to

determine if other light sensitive areas of the brain exist, and if

so, what impact they may have on physiologic processes such as

growth and lactation.

The manipulation of photoperiod and the resulting increase in

milk yield are of potential benefit to the dairyman. Electricity

for one 400 watt high pressure sodium vapor lamp would cost the

50

dairyman $49.70 per year if used for 18 h per day for six months

each year (based on March 1983 electricity prices for the Northwest

(3.780/kwh). Each lamp provides sufficient light to illuminate

251 square m at approximately 100 lux if positioned 6.5 m above the

barn floor. Each cow requires 8.7 square m of space, including

free stall, cow alley, feed manger, and feed alley space. One

fixture therefore would provide enough light for 29 cows.

As an example, assume that Joe Farmer has 100 cows with a

rolling herd average of 6306 kg milk with 3.5% butterfat. His

cows, on the average, are producing 5833 kg 4% FCM per year.

If, by providing supplemental light, 4% FCM is increased by 7%

as observed in our experiment, each cow will produce 204 kg more

4% FCM if increased lighting is effective for 6 months. At

current milk prices of $13.50 per cwt (29.760 per kg) and 170 fat

differential (for each 0.1% change from 3.5%) per cwt (.3750 per

kg), income would increase by $64.55 per cow. Approximately 30%

of most herds are first calf heifers and would not benefit from

the additional light. So additional income per year for the 70

mature cows would be $4518. Additional costs per year would include

the four lamps ($165 per lamp over 10 years expected life = $66

per year) and electricity ($49.70 per lamp X four lamps = $198.80),

giving a total cost per year of $264.80. Net additional income

would be $4253.20 or $42.54 per cow and a return per dollar invested

of $16.06. Additional savings in electricity may be realized if

future experiments using intermittent lighting, or light for 1-2

hours at specific periods of time after dawn, prove successful.

51

Our experiment has provided information useful to the dairy

farmer in Oregon. Providing cows with supplemental photoperiod can

provide substantial increases in income, which, in view of the current

milk surplus, would allow the dairyman to decrease herd size and

thus operating costs.

52

BIBLIOGRAPHY

Akers, R.M., D.E. Bauman, A.Y. Capuco, G.T. Goodman, and H.A.Tucker. 1981. Prolactin regulation of milk secretion andbiochemical differentiation of mammary epithelial cells inperiparturient cows. Endocrinology 109:23.

Barott, H.G., and E.M. Pringle. 1951. Effect of environment ongrowth and feed and water consumption of chickens. IV. Theeffect of light on early growth. J. Nutr. 45:265.

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APPENDIX

59

APPENDIX 1

Feed Intake

Feed intake data for Experiments 1 and 2 are presented in

Appendix Table 1. The amount of feed cows received was recorded

daily and amount of feed refused was recorded once weekly from

which total feed intake per group was calculated. Number of cow

days per group per week was used to calculate mean intake per cow

per day.

Data were analysed within experiments using a two by two

factorial design with photoperiod and age as the main effects. As

expected, cows ate significantly more (P<.01) than heifers in both

experiments. This can be attributed to higher metabolic body weights

and feed requirements of the cows. A significant treatment by age

interaction (P<.01) was observed in Experiment 2. Cows exposed to

18L:6D ate less than cows exposed to natural photoperiod (43.0±0.6 vs.

44.4±0.7 kg feed/day) whereas heifers exposed to 18L:6D ate more

than heifers exposed to natural photoperiod (40.3±0.6 vs. 38.3±0.5 kg

feed/day).

Regression analysis indicated that cows in Experiment 1 exposed

to 24L:OD increased feed intake while those exposed to 18L:6D de-

creased weekly feed intake over the length of the experiment

(Appendix Figure 1). Heifers in Experiment 2 ate less when ex-

posed to 18L:6D and increased feed consumption when exposed to

natural photoperiod (Appendix Figure 2).

Interpretation of these data must be made with care. In both

60

experiments dry matter intake was not calculated. Corn silage was

stored in a bunker silo which was partially open to environmental

conditions. During periods of heavy rains, dry matter in corn

silage, and therefore in the total ration, decreased. Other

commodities used in the ration were not subject to these open

conditions and maintained uniform dry matter.

Another important factor in interpreting these data is that

although experimental animals remained in the alleys for the length

of the experiment, nonexperimental animals were moved in and out

of the alleys at various times. Competition between cows and

competition for feed manger space therefore, changed from time to

time throughout the experiment. Prior to being introduced into

the groups, new cows were not always exposed to the same photo-

period as animals in the alley. The effect of photoperiod on feed

intake in these new animals would not be the same as the effect on

experimental animals because acclimation time to the new photo-

period was different. Therefore, it is not possible to draw firm

conclusions on the effect of photoperiod on feed intake from these

data.

Estrus detection during Experiment 1 was conducted using both

visual observation by experimenters and herd staff and KaMar Heat-

mount Detectors (KaMar, Inc., Steamboat Springs, CO). A summary

of the accuracy of the KaMar heat detectors is presented in

Appendix Table 2. Estrus was determined by visual observation

(e.g. standing to be mounted, mucus discharge), rectal palpation

at time of insemination, and subsequent rectal palpation of pregnancy.

61

Sixty-six percent of all cows in estrus had KaMar aids activated.

Thirty-seven percent of all KaMars activated were false positive.

Eighty-eight percent of first calf heifers in heat had KaMar aids

activated and 55% of all KaMars activated in this age group were

false positive. The increased activity of the younger animals

may account for the difference observed between age groups.

Other factors which may have affected the accuracy of the estrus

detection aids include the steep slope of the barn floor (4°),

which may have deterred the cows willingness to mount, and the

reproductive condition of the animals. This herd had a relatively

high incidence of cystic ovaries as diagnosed by rectal palpation

(39% of cows and 11% of heifers). Nymphomania and anestrus are

clinical signs of cystic ovaries and would affect the number of

false positive readings and total number of cows in observed

estrus, respectively. Nineteen percent of cows with activated

KaMars and 24% of heifers with activated KaMars were not observed

in estrus visually. Accuracy of estrus detection was determined

here by interval from previous estrus, or subsequent pregnancy

from breeding. These results indicate that KaMar estrus detection

aids can be used to assist in estrus detection, however due to

the high number of false positive readings, they should not be

used as the only method of estrus detection.

62

Appendix Table 1. Mean daily feed intake (kg feed as fed/cow/day)for Cows and Heifers in Experiment 1 and 2.

Experiment 1

Week

Cows

24L:OD 18L:6D

Heifers

24L:OD 18L:6D

1 44.0 42.6 46.9 40.52 46.4 46.5 40.3 37.53 45.5 45.3 41.9 40.84 44.5 51.4 44.5 45.05 41.1 45.3 38.8 42.96 40.7 40.0 39.6 44.37 43.8 41.4 41.8 38.58 42.9 42.1 40.1 38.89 44.5 42.2 40.3 37.3

10 42.8 39.3 41.4 37.011 51.2 42.5 41.9 39.8

Experiment 2

Week

Cows

NaturalPhotoperiod 18:6D

Heifers

NaturalPhotoperiod 18L:6D

1 44.2 44.9 37.2 40.12 42.1 43.0 38.5 42.2

3 44.4 42.1 35.4 42.0

4 46.5 44.0 39.9 43.6

5 48.7 44.2 39.6 40.7

6 45.8 44.0 36.7 39.7

7 44.6 45.6 40.7 41.8

8 45.7 42.1 40.0 39.4

9 42.9 42.2 37.1 36.5

10 41.3 39.2 39.4 38.5

11 40.8 39.6 35.4 38.5

12 45.8 45.8 40.2 40.8

Appendix Table 2. Accuracy of KaMar Heatmount Detectors in Cows and First Calf Heifers inExperiment 1.

Number ofcows in estruswith KaMaractivated

Number ofKaMar activatedcow not in estrus(False positive)

Number ofcow in estruswithout KaMaractivated

Number of cowsin estrus with KaMaractivated but no visualobservation of heat

Cows 30 17 15 7

First calf heifers 30 37 4 16

64

Appendix Figure 1. Mean kilograms feed consumed (as fed) per dayfor cows exposed to two photoperiods (18L:6Dand 24L:OD).

50

)-

0

El 45

0)ct

ist

3d 24L : OD

0

3 40wIt.

APPENDIX

FIGURE I

CD

35

V

10

0

66

Appendix Figure 2. Mean kilograms feed consumed (as fed) perday for heifers exposed to two photoperiods(18L:6D and natural).

45

>-

0

0o0 40wLA.

rnaow2mcozoo 350wwk.oX

30

;0

7

/c-1o- 0/ \

18L:66-- -- --

APPENDIX

FIGURE 2

NaturalPhotoperlod

I I I 1 i 1 t 1 1 I I2 4 6 8 10 12

WEEKS