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FOLLICULOGENESIS IN SWINE: EFFECTS OF UNILATERAL
OVARIECTOMY ON SUBSm,UENT OVULATORY
COMPENSATORY HYPERTROPHY DURING
THE ESTROUS CYCLE
by
LARRY M. WIGINTON, B.S.
A THESIS
IN
ANIMAL BREEDING
Submitted to the Graduate Faculty of Texas Tech University in
Partial Fulfillment for the Requirements for
the Degree of
MASTER OF SCIENCE
Approved
'I Accepted
May' 1980
ACKNOWLEIX; EMENTS
Sincere appreciation for the help and guidance in the preparation
and writing of this thesis is given to my advisory committee consist-
ing of my major advisor, Dr. J.R. Clark, and Drs. L.F. Tribble and
M. Hughes. Also, I would like to express my appreciation to my fel-
low students C. Kelly, A. Komkov, and S. Fooshee for their help and
advice in carrying on my research. In addition, the technical as-
sistance of Jose and Jorge Navar and JoAnne McKinlay was most help-
ful. To my wife, Dianna, who encouraged me and typed this thesis, I
am always indebted.
ii
TABLE OF CONTENTS
ACKNOWLEI:X; EMENTS
LIST OF TABLES
LIST OF FIGURES
Chapter I INTRODUC'riON
Chapter II LITERATURE REVIEW
Chapter III EFFECTS OF UNILATERAL OVARIEC'rOMY AT DIFFERENT STAGES OF THE ESTROUS CYCLE ON FOLLICULAR MATURATION AND OVULATION RATE IN GILTS
Summary Introduction Materials and Methods Results and Discussion
Chapter IV TIME OF THE ONSET OF ESTRUS IN THE SOW
Summary Introduction Materials and Methods Results and Discussion
LITERATURE CITED
APPENDIX
iii
ii
iv
v
1
J
12 13 14 15
25 25 26 26
31
35
LIST OF TABLES
III-1. Assignment of Experimental Units to Treatment Groups and their Fate 16
III-2. Means (+ SE) for Age at First Estrus for Gilts Used 17
III-3. Mean (± SE) Estrous Cycle Length as Affected by Treatment, Cycle and Treatment X Cycle Interaction 19
III-4. Least Square Heans (± SE) and Orthogonal Comparisons for the Number of Corpora Lutea in Gilts Following Unilateral Ovariectomy on Various Days of the Estrous Cycle 20
Appendix Tables
1. Analysis of Variance Table for Age at First Estrus
2. Analysis of Variance for the Length of the Control and Treatment Estrous Cycles
3. Analysis of Covariance and Orthogonal Comparisons for the Number of Corpora Lutea (Ovulation Rate)
4. Analysis of Variance for Number of Medium and Large Follicles and Total Number of Follicles
5. Chi-square Analysis for Time of Day of Onset of Estrus
iv
36
37
38
39
40
LIST OF FIGURES
III-1. Means (+ SE) for the Number of Medium and Large Follicles and the Total Number of Follicles on the Right Ovary on Day 13, 15, 17, and 19 of the Estrous Cycle
IV-1. Percentage of Gilts Showing the Onset of Behavioral Estrus in Relation to the Time of Day
v
24
28
CHAPTER I
INTRODUCTION
The study of reproduction of the domesticated farm animals is a
vast and exciting field. It has diverged into such areas as physiology,
endocrinology, and behavior of the animal during the different stages of
reproduction. Yet, as more knowledge is gained many new doors to these
various areas of research will be opened.
Utilization of knowledge obtained in the last few years is requir
ing re-evaluation of such subjects as compensatory hypertrophy following
removal of one ovary from the female. The mechanism by which the re
maining ovary is able to increase the number of follicles which will
mature and ovulate following removal of that ovary's mate is complex
and little understood. This compensation is thought to involve a de
crease in the number of follicles which normally become atretic due to
minute and short-lived rises of follicle-stimulating hormone (Benson
et al., 1969; Welschen and Dallaart, 1964; and Butcher, 1977).
The purpose of this study is two-fold and utilizes the pig as the
experimental animal because of its multiparous reproductive status. The
first study was to determine the time during the porcine estrous cycle in
which compensation in ovulation rate following unilateral ovariectomy will
cease to occur, thus yielding knowledge of the length of time required
for follicular development. The second study was to determine when the
onset of behavioral estrus occurs in relation to the time of day.
1
2
The knowledge from these two studies when added to the vast amount
of knowledge we now have and future knowledge yet to be gained may lead
to new and more productive ways of producing livestock to meet the food
needs of today's growing world population.
CHAPTER II
LITERATURE REVIEW
Unilateral ovariectomy (ULO) is an event which has held the inter
est of researchers for over a century. Following removal of one ovary
from a female, nature has developed a system by which the remaining
ovary will develop a larger than normal number of follicles to compen
sate for the loss of the other ovary. Hunter (1787) was the first in
vestigator to show compensatory hypertrophy following removal of one
ovary. Since that time many researchers have looked at areas of this
phenomenon in many species, including domestic farm animals. These
investigations have contributed greatly to the knowledge of ovarian
function; but much work remains to be done.
Many studies of the effects of ULO have been done utilizing labor
atory animals such as the rat. Doncaster and Marshall (1910) found no
differences in the sex of the offspring following ULO, however, an
increased number of corpora lutea was found showing that compensatory
hypertrophy did occur. Hatai (1913) found that body growth is modified
by ULO in the albino rat. No change was found in the weight of the
hypophysis following ULO, but the remaining ovary compensated in both
weight and ovulation rate. Arai (1920) found that removal of one ovary
before puberty causes the remaining ovary to be approximately 40%
heavier than that of the controls. The surviving ovary also had a
greater number of follicles than the controls. Also, the surviving
3
4
ovary exhibited a definite amount of hypertrophy within a short time
after ULO (three to five weeks) though its increase was not so large as
that found in the surviving ovary of adult animals. After the appear
ance of corpora lutea (CL), the remaining ovary was more than 100% heavi
er than either ovary of the controls. In rats, when one ovary was re
moved, there was a slight decrease in the number of young born when com
pared to the number of CL on the remaining ovary. Slonaker (1927) found
his rats to have an average of 5.25 young born and 8.9 CL following ULO
as compared to an average 6 . 9 young born and 9. 6 CL in the controls. ULO
mice had the same mean number of offspring as did controls; although the
total number of litters and the total offspring per mouse were about half
that of the controls. The total young produced per female by one ovary
mice was 56% of that by two ovary mice which is not different (P>.05)
from hypothetical 50% (Jones and Krohn, 1960; Biggers et al., 1962).
The number of primordial oocytes on the remaining ovary following
ULO remained at normal levels for each ovary of an intact rat. The
ovary doubled in weight, and produced as many mature Graffian follicles
as were found in the two ovaries of litter mate controls (Mandl and
Zuckerman, 1951). During the estrous cycle of intact rats, there was a
gradual increase in the number of follicles with a diameter of 518 to
571~ and greater, however, the total number of follicles ranging in size
from 352 to 371~ remained constant. Depletion of follicles measuring
395 to 570~ occurred by proestrus. Unilateral ovariectomy on the day of
estrus resulted in a temporary decrease in the number of follicles larger
than 448\.l. The remaining ovary of these animals showed a significant
increase by the next estrus in the number of follicles greater than
448~. Compensatory ovulation in the rat involves doubling the number
of large follicles which ultimately mature during the estrous cycle.
This results from increased proliferation of smaller follicles in the
course of the cycle rather than from decreased follicular atresia
(Peppler and Greenwald, 1970). Unilateral ovariectomy also causes
ovarian compensation in pseudopregnant and pregnant rats. This causes
increased numbers of antral follicles within five days and compensatory
ovulation at postpartum estrus (Chatterjee and Greenwald, 1971).
5
The rabbit also exhibited compensatory hypertrophy following par
tial removal of the ovarian mass. Both pregnant and nonpregnant rab
bits yield the same number of young or ova, respectively, when one to
one and one-half ovaries were removed (Carmichael and Narshall, 1908).
When prepuberal rabbits had one-half to five-sixths of the total ovarian
mass removed, the size of litters were found to be the same as controls
after puberty. However, the incidence of fetal atrophy was greater in
the treated animals. It can be assumed that hypertrophy of the remain
ing ovarian tissue occurs to a varying degree, and is proportionally
greater as more ovarian mass is removed (Asdell, 1924).
Studies dealing with compensation after ULO have been conducted
in other species. In the opossum, ULO resulted in complete compensa
tion (Hartm&~, 1925). Cochrane and Holmes (1966) found that the rhesus
monkey also exhibited ovarian compensatory hypertrophy following ULO.
Therefore, the ability of the ovary to compensate for loss of ovarian
material is not just in rodents, but has been found in the higher mam
mals as well.
6
The sheep and cow have some differences in their reproductive abi
lities. The main difference to be considered is that the ewe normally
ovulates one to three eggs while the cow usually ovulates only one egg.
Sundaram and Stab (1967) removed either the left or right ovary and com
pared these to a control group. The lamb crop of the intact ewes was
significantly greater than that of the ULO ewes, but there was no dif
ference between the left or right ULO ewes. Land (1973) found, in con
trast, that unilateral ovariectomy on. days 2, 8, or 14 did not affect
the total number of eggs shed at the next estrus when both ovaries had
CL. Removal of the ovary with a CL, when only one ovary has a CL, will
result in shortening the length of that cycle. Total follicular fluid
weight and number of follicles above 5 mm in diameter showed significant
compensatory hypertrophy, but only if a CL was present in the ovary
(Mallampati and Casida, 1970). The same results were also seen in the
cow. If the ovary containing a CL is removed on day 8 of the cycle, the
estrous cycle length was shortened. The total follicular surface area,
however, was almost twice as large as that of the corresponding ovary
of an intact cow, demonstrating compensation as seen in other species
following unilateral ovariectomy (Saiduddin et al., 1970).
The porcine is a very good domestic animal to use for ovulation
rate studies and several experiments have been conducted with this spe
cies. One study by Hunter (1787) was the first recorded experiment in
which one ovary was removed and he found that removal of one ovary from
a sow resulted in the remaining ovary ovulating ova equal to the number
normally produced by both ovaries. In addition, the sow with one ovary
only produced 60% of the total pigs (eight litters) as the norma.l sow
7
(13 litters). The removal of one ovary from gilts has confirmed Hunter's
results with respect to ovulation rate. The unilaterally ovariectomized
animals ovulate the same number of ova as normal animals with both ovaries
(Brinkley et al., 1964; Brinkley and Young, 1969).
Removal of one ovary during early pregnancy resulted in increased
ovarian and corpora lutea weight and larger graafian follicle size in
the remaining ovary indicating compensatory hypertrophy similar to the
nonpregnant pig (Rathmacher et al., 1967; Rexroad and Casida, 1976).
Ovarian function is controlled by a complex system of hormones and
uterine factors. The resulting compensatory hypertrophy following ULO
was postulated by Lipschutz (1925) to be due to some general factor,
possibly to some substance available in the body in a given amount. It
is now known that follicle stimulating hormone (FSH) and luteninizing
hormone (LH) are the two gonadotropins involved in follicular formation
and ovulation.
Lesions in the anterior hypothalamic area will cause rats to exhibit
estrus interrupted by vaginal smears of diestrous type. Absence of
compensatory hypertrophy of the remaining ovary following ULO suggests
that nervous elements localized in this region play an essential role in
the stimulation of gonadotropin output by diminution of the blood es
trogen level (Flerko and Bardos, 1961). Rats immunized against LH-RH
showed abolition of regular cyclic patterns which indicated blockage of
FSH and LH production (Fraser and Baker, 1978).
Pregnant Mare Serum Gonadotropin (PMSG), which has characteristics
of both FSH and LH, causes the remaining ovary of unilaterally ovariec
tomized rats to ovulate as many ova as both ovaries of controls when
8
treated with 15 International Units (IU). Increasing the dosage to 30
IU caused the controls to ovulate more ova than the one-ovary animals.
This was probably due to ovulation being at a maximal rate in the one
ovary rats (Zarrow et al., 1965). The injection of 15 IU of PMBG will
cause the same relative compensatory ovulation rate as the removal of one
ovary. The compensatory mechanism has been associated with FSH. Biolo
gical assays have shown no measurable alteration in gonadotropins, but
it was postulated that ovarian compensatory hypertrophy was due to in
creases in both serum and pituitary gonadotropins too subtle to be de
tected by biological assays (Edgreen et al., 1965). Greenwald (1968),
working with hypophysectomized rats given a single injection of PHSG,
found that the changes in ovulation and ovarian weight in the ULO rats,
in response to HCG, were only half that of the controls. He concluded
that increased availability of gonadotropins to the single ovary were
not responsible for the compensatory changes. Closer monitoring of the
concentrations of serum FSH have shown transient increases. It appeared
that removal of one ovary results in a decreased blood estrogen level
which may alter the feedback control of estrogen on the pituitary causing
a change in FSH. Following hypertrophy, the levels of FSH returned to
preoperative levels (Benson et al., 1969). Welschen and Dullaart (1974)
found that five hours after ULO a significant rise in FSH occurred. FSH
levels returned to control values between 16 and 24 hours after the op
eration. It was suggested that compensatory follicular growth was ini
tiated by a sharp increase in FSH levels. Butcher (1977) found a surge
of FSH lasting 6 to 18 hours following ULO.
9
Ovarian steroid hormones consist of estrogens and progesterone.
Each hormone has a feedback mechanism which acts back on the hypothala
mus. Both progesterone and lower concentrations of estrogen inhibit FSH
secretion by negative feedback. Estrogen, after reaching a higher con
centration, however shifts to a positive feedback causing an increased
secretion of FSH. If compensatory hypertrophy is due to a transient
rise in FSH, steroid hormones would be expected to block the compensa
tion. Progesterone injections have been shown to block compensatory
hypertrophy 100% with very little effect on normal activity of each
ovary in the pig (Short et al., 1968a) and in the rat (Peterson et al.,
1964; Jelinek et al., 1968). Compensatory hypertrophy following unila
teral ovariectomy in pregnant rats can also be blocked by treatment on
day 10 by either progesterone or estradiol cyclopentlypropionate for 4
days (Chatterjee and Greenwald, 1971).
FSH acts at the ovarian level to stimulate the developing follicles
to produce estrogens. The removal of one ovary should alter in some way
the level of estrogens being produced. Removal of one ovary from preg
nant gilts on day 4 or 15 causes the remaining ovary to increase the
growth rate of follicles to a larger size than in controls. EStradiol-
178 content of follicular fluid more than doubles in the one remaining
ovary when compared to only one ovary of an intact animal. This in
creased content is due to increased follicle size as unilateral ovari
ectomy did not affect the concentration of estradiol-178 in follicular
fluid thereby suggesting that the steroid synthesizing activity of
follicles increase with the increase in follicle size of the rema.ining
ovary (Rexroad and Casida, 1976).
10
The effects of unilateral ovariectomy are to increase the number
and size of follicles, increase the weight of the ovarian stroma, and
generally compensate for the loss of the other ovary. This process re
quires a certain time period. When unilateral ovariectomy was performed
on each day of the hamster's four day cycle, compensation caused a
doubling of follicles on the first two days, but no compensation was
seen on the last two days (Greenwald, 1960). Repetition of this study
by Greenwald (1961) showed that removal of one ovary during the first
three days of the estrous cycle was followed by a doubling of the ovu
lation rate from the remaining ovary. Hamsters were unilaterally ovari
ectomized on day three of the estrous cycle at 0900, 1600, or 2000 hours.
The remaining ovary then ovulated an average of 11.6, 9.2, and 5.7 ova,
respectively. Therefore, the gradual decline in the ovulatory response
was associated with atresia involving the smaller follicles that had
developed during the cycle as compensatory hypertrophy decreased (Green
wald, 1962). The compensatory response in the guinea pig caused a
doubling of ova through day 12. Day 12 seems to be the critical period
of the guinea pig cycle. After this time, the ability of the animal to
compensate for unilateral ovariectomy is lost (Hermreck and Greenwald,
1964).
Little work has been done involving the day of the estrous cycle
in swine where ovarian compensation ceases to increase the ovulation
rate. Removal of one ovary in gilts on days 1, 7, or 13 of the estrous
cycle resulted in compensatory hypertrophy at the subsequent estrus
(Short et al., 1968b). The pig, therefore, is able to compensate for
removal of one ovary through day 13 of the estrous cycle. The period
when compensation ceases, as found in the hamster and guinea pig, has
not been established in the pig.
11
CHAPTER III
EFFECTS OF UNILATERAL OVARIECTOMY AT DIFFERENT STAGES OF THE ESTROUS CYCLE ON FOLLICULAR MATURATION
AND OVULATION RATE IN GILTS
s Ullliilary
The objective of this study was to determine when during the cycle
after unilateral ovariectomy (ULO) the remaining ovary fails to compen-
sate in ovulation rate for the loss of the other ovary. At their sec-
ond estrus (day 0 of the cycle), 25 crossbred gilts were randomly as-
signed (5 per group) to one of the following treatment groups: (a)
Control, (b) ULO on day 13 of the estrous cycle, (c) ULO on day 15, (d)
ULO on day 17 or (e) ULO on day 19. At surgery, the right ovary was re-
moved and the number and size of follicles were recorded as medium (3 to
6 mm diameter), large (?..7 mm) and total (?_3 mm). The length of the con
trol cycle before (19.6 days) and of the cycle during (20.1 days) ULO
was not different (P>.05). The least-square means (±SE) for ovulation
rate as affected by treatment were: (a) 14.1 ± 1.2, (b) 14.1 ± 1.2,
(c) 10.2 ± 1.2, (d) 9.5 ± 1.2 and (e) 9.4 ± 1.2. Ovulation rate was
decreased (P<.03) when the ovary was removed on days 15, 17, or 19 as
compared to day 13 and the control group, the number of medium follicles
and the total number of follicles in the right ovary decreased (P<.05)
by 91 and 61%, respectively, from days 13 to 19, while the number of
large follicles increased (P<.01) by 81% during the same time period.
In conclusion, by day 15 of the estrous cycle, the follicles remaining
12
13
on the ovary after ULO are either destined to ovulate or become atretic.
Apparently those follicles not destined to ovulate are atretic and can-
not be rescued so that compensatory hypertrophy could occur after day
15 of the estrus cycle.
Introduction
Hunter (1787) noted that the removal of one ovary from the sow did
not decrease litter size. Since then, the remaining ovary after unila
teral ovariectomy (ULO) ovulated approximately the same number of folli-
cles as both ovaries in the control gilts (Brinkley et al., 1964; Brink
ley and Young, 1969; Short et al., 1968a,b). --- --Unilateral ovariectomy during the first three days, but not during
the last day, of the estrous cycle of the hamster results in a doubling
of the number of ovulations from the remaining ovary at the next estrus
(Greenwald, 1960, 1961). In the guinea pig, when the ULO was performed
after day 12 of the estrous cycle, the remaining ovary did not compen-
sate in ovulation rate for the loss of the other ovary.
When all visible surface follicles were cauterized on day 16 of the
estrous cycle in gilts, the cycle length was increased by approximately
4 days indicating that the follicles that were destroyed on day 16 were
part, if not all, of the ovulatory crop (Clark et al., 1979; Kelly, 1979).
Therefore, the objectives of this study were to determine: (1) the time
period of the estrous cycle following ULO that the remaining ovary fails
to compensate for the loss of the other ovary in the pig and (2) the
number of follicles on the removed ovary at various stages of the es-
trous cycle.
14
Materials and Methods
Thirty-three three-way crossbred gilts, weighing approximately 91
kg, were allotted to this study from a large pool of gilts. They were
penned in a dirt lot, next to a boar, and checked for behavioral estrus
once daily. Each gilt was allowed to complete one estrous cycle (con
trol) before being assigned to a treatment group. At their second es
trus (day 0 of the estrous cycle), each gilt was randomly assigned to one
of five groups: (a) Control--gilts not subjected to surgery, (b) ULO on
day 13 of the estrous cycle, (c) ULO on day 15, (d) ULO on day 17 or (e)
ULO on day 19. Each treated gilt was injected with 1 g sodium thio
pental (Dipentol; Diamond Laboratories, Inc., Des Moines, IA) intraven
ously to induce anesthesia which was maintained during surgery by a mix
ture of nitrous oxide, oxygen and methoxyflurane (Metophane; Pitman
Moore, Inc., Washington Cross, NJ) administered through a closed-circuit
system (Dziuk et al., 1964). A mid-ventral laparatomy was performed, the
right ovary exposed and surgically removed. Following the surgery, the
number and size of the follicles on the right ovary were recorded. Cal
ibrated wire loops were used for measuring the diameter of each macrosco
pically visible surface follicle >3 mm which was then punctured after
being measured. The follicles were then arbitrarily grouped as medium
follicles (J to 6 mm), large follicles (~7 mm) and total number of fol
licles (>3 mm; Clark et al., 1972). The gilts were slaughtered within
two weeks following their third estrus. The ovaries were removed, trimmed
free from the mesovaria, and the number of corpora lutea (CL) were coun
ted. In the control gilts, the number of CL on both ovaries were used
as the ovulation rate; whereas, in the ULO gilts the number of CL from
15
the remaining ovary was used as the ovulation rate.
The data for age at first estrus, estrous cycle length, the num
bers of medium and large follicles and the total number of follicles
were analyzed by a completely random design analysis of variance and
Duncan's New Multiple Range Test. The number of CL were analyzed by
the analysis of covariance with the length of the treatment estrous cy
cle used as the covariate. Differences between the adjusted least square
means were determined by a set of orthogonal comparisons (table III-4).
Chi-square analysis was used to determine if differences existed in the
number of animals assigned to the study vs. number of animals contribu
ting data to the study (Steel and Torrie, 1960).
Results and Discussion
Of the 33 gilts assigned to this study, 8 did not provide useable
data (table III-1) due to the development of follicular cysts. Other
workers have reported the development of follicular cysts after surgical
manipulation of the ovaries during the estrous cycle in gilts (Brinkley
et al., 1964; Short, 1967; Short et al., 1968a; Brinkley and Young 1969).
The average (+standard error of the mean, SE) age of the gilts at
their first estrus was 271.3 ± 22.4 days, there being no treatment dif
ferences (P<.05) in age among the gilts (table III-2 and appendix table
1). However, there was a tendency (P<.10) for the gilts in the day 17
group to be younger and those in the day 19 group to be older at first
estrus with the gilts in the remaining groups to be intermediate and
not different from either of the above two groups. No differences
(P>.05) in estrous cycle length (in days) due to treatment, cycle or
TABLE III -1. ASSIGNNENT OF EXPERD1ENT AL UNITS TO TREATMENT GROUPS AND THEIR FATE
Treatment No. gilts No gilts groups assigned a providing datab
Control 6 5
Day 13 6 5
Day 15 6 5
Day 17 7 5
Day 19 8 5
~ollicular cysts developed in 1, 1, 1, 2 and 3 gilts, respectively. The data from these gilts were excluded from the experiment.
bx2 - 1 4 4 - . , ns.
16
TABLE III-2. HEANS ( + SE) FOR AGE AT FIRST ESTRUS FOR GILTS USED
Treatment group
Control
Day 13
Day 15
Day 17
Day 19
Number of gilts
5
5
5
5
5
Age at first est:::::-1-.lS, days
290.2 :t 26.6ab
267.4 ± 15.8ab
.256.4 ± 21.4ab
239.0 ± 16.8ab
302.8 ± 28.6a
a, bNeans with different superscripts di:fer significantly (P< .10).
17
18
treatment X cycle interaction (table III-3 and appendix table 2). This
indicates that the surgical procedure did not have an effect on the length
of the treatment estrous cycle when compared to the length of the control
cycle.
The ovulation rate of the left ovary, adjusted for the length of the
treatment estrous cycle, at the estrus following ULO on day 13, 15, 17
or 19 was compared with the ovulation rate of both ovaries from the con
trol gilts (table III-4 and appendix table 3). The mean ovulation rate
of the control group (14.1) was different (P<.02) from the mean of the
remaining groups (10.8). The mean ovulation rate of the day 13 group
(14.1) was different (P<.005) from the combined means of the day 15, 17
and 19 groups (9.7). The mean ovulation rate of the day 15 group (10.2)
was not different (P>.50) from that of the day 17 and 19 groups (9.46).
Additionally, the mean ovulation rate of the day 17 group (9.5) was not
different (P>.90) from that of the day 19 group (9.4).
The remaining ovary following ULO had sufficient time to develop
additional follicles to compensate for the loss of the other ovary when
ULO was performed on day 13 confirming the data of Short et al., (1968b).
However, when ULO was performed after day 13, the remaining ovary did
not have sufficient (non-atretic) follicles to allow for compensation of
the loss of the other ovary. The rate of compensation was 68.e%. Since
it has been established that the pig has a higher proportion of ovula
tions in the left (.55) than in the right ovary ( .45; Warwick, 1926;
Clark et al., 1975), the rate of compensation should have been lower if
the left ovary had been removed in this study rather than the right ovay.
The results of this study indicate that on or after day 15 of the estrous
19
TABLE III-3. MEAN (± SE) ESTROUS CYCLE LENGTH AS AFFECTED BY TREATMENT,
Treatment group
Control
Day 13
Day 15
Day 17
Day 19
CYCLE AND TREAU1ENT X CYCLE INTERACTION
Cycle Estrous cycle length,
Control 18.8 + 0.4a Treated
- a 19.2 ± 0.6
a Control 19.8 + 0.7 - a Treated 19.2 ± o.s
a Control 18.8 + 0.8 - a Treated 19.6 ± 1.1
Control 19.6 + 0.7a - a Treated 21.8 + 1.8
a Control 21.2 + 1.0 - a Treated 20.6 + 1.4
~eans with same superscript are not different (P>.05).
days
20
TABLE III-4. LEAST SQUARE MEANS (± SE) AND ORTHOGONAL COMPARISONS FOR THE NUMBER OF CORPORA LUTEA IN GILTS FOLLOWING UNILATERAL OVARIECTOMY ON VARIOUS DAYS OF THE ESTROUS CYCLE
Treatment Number Adjusted number Orthogonal comJ2arisons group of gilts of corpora luteaa I II III I~l
Control 5 14.1 ± 1.17 +
Day 13 5 14.1 ± 1.17 +
Day 15 5 10.2 ± 1.16 +
Day 17 5 9 ·5 ± 1.22 +
Day 19 5 9.4 ± 1.16
Probability of a difference P<.02 P<.005 P>.50 P>.90
~he number of CL were adjusted for the length of the treatment estrous cycle.
21
cycle in the pig the follicles on the ovary are of two primary classes:
1) follicles that have been selected to ovulate at the next estrus and
2) follicles that cannot respond to the stimulus of ULO and therefore
doomed to become atretic. These results in the pig are like those found
for laboratory animals. In hamsters, Greenwald (1960, 1961) found that
following ULO during the first three days of the four-day cycle, the re-
maining ovary was capable of compensating in ovulation rate for the loss
of the other ovary. Similarly, the ability of the guinea pig to compen-
sate in ovulation rate was lost after day 12 of the estrous cycle (Herm-
reck and Greenwald, 1964).
The results of the present study complement the study in which fol-
licles were cauterized at various days of the estrous cycle in the pig
(Clark et al., 1979; Kelly, 1979). In that study, destruction of all
macroscopically visible follicles at day 16 but not at day 14 of the
cycle resulted in a lengthening of the cycle without affecting ovulation
rate, indicating that the follicles destined to ovulate were selected
by day 16 but not by day 14.
The mechanism involved in compensatory hypertrophy appears to be
due to a transcient rise in follicle-stimulating hormone (FSH) following
ULO (Benson et al., 1969; Welschen and Dullaart, 1974; Butcher, 1977) --resulting in the rescue of follicles which normally would have become
atretic (Greenwald, 1962; Rexroad and Casida, 1976). In the present
study, either the transcient rise in FSH following ULO at days 15, 17
or 19 failed to occur in the pig or that the follicles that were pre-
sent on the ovaries were already in the process of becoming atretic and
could not respond to the rise in FSH.
22
The number of follicles of the various size classifications were
counted on the right ovary which was removed during ULO on days 13, 15,
17 or 19 of the estrous cycle (figure III-1 and appendix table 4). The
number of medium follicles (3 to 6 mm diameter) were not different
(P>.05) between days 13 and 15, days 15 and 17, but there were fewer
(P<.05) follicles at day 17 than at day 13. There were fewer (P<.05)
medium follicles at day 19 when compared to days 13, 15 and 17. The num
ber of large follicles (>7 mm diameter) were not different (P>.05) at
days 13 (1.4), 15 (0.0) and 17 (2.2), but increased (P<.01) at day 19 to
7.2 follicles. The total number of follicles (>3 mm diameter) did not
differ (P>.05) between days 13, 15 and 17, however there was a tendency
for the numbers to be less (P<.10) on day 17 than on day 13. The fewest
(P<.05) total number of follicles was seen on day 19. This data suggests
that as the estrous cycle progresses there is a decrease in the total
number of follicles >3 mm in diameter on the right ovary from a mean of
23.4 + 3.1 on day 13 to a mean of 9.3 + 0.6 on day 19 of the estrous cy-- -
cle with a gradual shift from medium to large follicles during the same
time period which supports the data of Clark (1974).
The study of ovarian function, as exemplified by determination of the
critical period for ovulatory compensation following ULO and the shifts
in follicular size, will yield much valuable information which will be
of great help in future attempts to manipulate the reproductive cycle.
This manipulation may someday help produce more livestock on a per unit
basis than is possible today.
23
~igure III-1. Means (+ SE) for the number of medium and large follicles and the total number of follicles on the right ovary on days 13, 15, 17, and 19 of the estrous cycle. a,b,c Means with different superscripts differ (P<.05). d,e Means with different superscripts differ (P<.01).
24
E 2 s~ Ta -E T a,b
c.c ~ -0 Tb ...
M 15 1- -.. E ::3 ·- ~ ~ -Q)
:E 5 1- -
-rC
en w ....J u E ....J E 10 ....J ~ -0 " u. 1\\ Te u. . 0
Q) ..
C)
a: .... ca 5 ~ w ....J -
Cil -rd :E Td :::>
z
25 - Ta -E Ta E ~ Ta -
M
" 15 - -.. -ca ... 0 ~ -.b ....;
~
5 - -
13 15 17 19
DAYS OF THE ESTROUS CYCLE
CHAPTER IV
TIME OF ONSET OF ESTRUS IN GILTS
Swnmary
This study was designed to determine when, during a 24-hr period,
gilts show the first signs of behavioral estrus. Beginning on day 16
of their first estrous cycle, 42 crossbred gilts were observed with the
aid of a boar for the onset of her second estrus at 0600, 1200, 1800 and
2400 hours. Twenty-three (55%) gilts showed the first signs of behav
ioral estrus at 0600 hours. None of the gilts were observed to have the
onset of estrus at 1200 hr; whereas, 10 (24%) and 9 (21%) gilts showed
the first signs of estrus at 1800 and 2400 hr, respectively. Chi-square
analysis demonstrated that more (P<.025) gilts had the onset of estrus
at 0600 hr than at 1200, 1800 and 2400 hours. If the data are combined
to center around estrous checks at 0600 and 1800 hr, 32 (76%) of the
gilts had their onset of behavioral estrus at 0600 hr as compared to 10
(24%) gilts at 1800 hr (P<.005). In conclusion, more gilts showed the
onset of behavioral estrus at 0600 hr than at any other of the times
examined.
Introduction
The time of the onset of estrus in relation to the time of day has
received little attention in the pig. Burger (1952) using cycling gilts
and sows and sows at their post-weaning estrus found no significant dif
ference in the number of animals exhibiting the onset of estrus during
25
26
the day or night. Differences may exist, however, between gilts and
sows in the time of day of the onset of estrus. It is, therefore, the
purpose of this study to investigate the patterns of estrous occurrence
during a 24-hr period in the gilts.
Materials and Methods
Forty-two three-way crossbred gilts were checked, using an intact
boar, once each day until their first estrus (day 0 of the estrous cy
cle) was observed. Beginning on day 16 of the second cycle, each gilt
was observed every six hours (0600, 1200, 1800 and 2400 hr) until the
mounting of the boar (mating was not allowed) was noted. The immobile
stance of the gilt while the boar mounted was taken as the onset of es
trus (Signoret, 1970). The time of day that each gilt showed the onset
of estrus was recorded and analyzed using the method of chi-square
(Steel and Terrie, 1960). When the gilts were observed at times when
natural lighting was not adequate, artificial lighting was used. All
observations were made between October, 1978, and April, 1979. All gilts
were examined for the evidence of ovulation 13 to 19 days after estrus.
Results and Discussion
The results are summarized in figure 1. Twenty-three of the 42
(54.8,%) gilts showed the first signs of behavioral estrus at 0600 hours.
None of the gilts were observed to have the onset of estrus at 1200 hr;
whereas, 10 (2J.8%) and 9 (21.4%) gilts showed the onset of estrus at
1800 and 2400 hr, respectively. Chi-square analysis showed that more
(P < .025) gilts had their onset of estrus at 0600 hr when compared to
1200, 1800 and 2400 hours.
27
Figure IV-1. Percentage of gilts showing the onset of behavioral estrus in relation to the time of day. The number above each bar indicates the number of animals at each time period.
w (.!)
~ z w (.) 0: w 0..
0 Ln
0 -
0 rt')
0 N
0 -
0 0 ~
0 0 co -
0 0~ -
0 0 (S) 0
~ 0 u.. 0 UJ ~ -1--
28
All gilts in this experiment had ovulated at the observed estrus
when laparotomized during the luteal phase of the cycle.
29
If the data are combined into a sunrise and sunset group ( 0600 and
1800 hr), 32 of 42 (76.2%) gilts had the onset of behavioral estrus at
sunrise compared to 10 of 42 (2J.8%) gilts at sunset (P<.005).
The results of the present study show that the occurrence of es
trus in the gilt is dependent on the time of day with the largest per
centage of gilts exhibiting the first signs of behavioral estrus at
0600 hours. This data is at variance with that of Burger (1952) who
found no effect of time of day on the onset of estrus. His data, how
ever, was a combination of results from gilts, sows and sows at their
post-weaning estrus. Because the data in the present study included
only gilts, it is not known whether the reproductive state and age has
an effect on the timing of the onset of behavioral estrus in swine.
Data from other species are just as confusing as the data from
swine. In the ewe, Hutchinson et al. (1964) showed that more ewes came
into estrus between 06JO and 07JO hr than at any other time period,
while Robertson and Rakha (1965) found that equal numbers of ewes coming
into estrus during the periods of 0400 to 1100 and 1JOO to 2200 hr with
the mean times being at sunrise and sunset. In the bovine, Trim berger
(1948) reported that dairy heifers and cows came into estrus at anytime
during the day or night, while Anderson (1944) found that 60%.of the
beef heifers and cows showed the onset of estrus between 0600 and 0900
hr and 1500 and 1800 hr with 38% of then beginning their estrous period
between 0600 and 0900 hours.
The results of the present study indicate that more gilts start
their estrous period between 0000 and 0600 hr than at any other six
hour period of the day. Since more gilts show the onset of estrus in
the early morning hours, a more accurate timing of breeding can be
attained if estrus is observed at that time. For research purposes,
a more accurate timing of the events occurring near ovulation can be
achieved.
30
LITERATURE CITED
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Clark, J.R. Thesis.
1974. Factors that alter ovulation rate in swine. University of Wisconsin Library, Madison.
31
Ph.D.
32
Clark, J.R., R.A. Dailey, N.L. First, A.B. Chapman, and L.E. Casida. 1972. Effect of feed level and parity on ovulation rate in three genetic groups of swine. J. Anim. Sci. 35:1216.
Clark, J.R., R.A. Dailey, R.B. Staigmiller, N.L. First, A.B. Chapman and L.E. Casida. 1975. Observed associations between corpora lutea and follicular development in swine ovaries during the estrous cycle. J. Anim. Sci. 41:1693.
Clark, J.R., C.A. Kelly, D.E. Orr, Jr. and L.F. Tribble. 1979. Folliculogenesis in swine: Effects of follicle-cautery on subsequent ovulation rate and estrous cycle length. Proc. Amer. Soc. Anim. Sci. (Southern Section), Abstr. No. 28, p. 11.
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Greenwald, G.S. 1962. Temporal relationship between unilateral ovariectomy and the ovulatory response of the remaining ovary. Endocrinol. 71:664.
Greenwald, G.S. 1968. Influence of one or two ovaries on ovulation and ovarian weight in the hypophysectomized rat. Endocrinol. 82:591.
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33
Hatai, S. 1913. The effect of castration, spaying, or semispaying on the weight of the central nervous system and the hypophysis of the albino rat; also the effect of semispaying on the remaining ovary. J. Exp. Zool. 15:297.
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Hunter, J. 1787. An experiment to determine the effect of extirpating one ovarium upon the number of young produced. Phil. Trans. 77:233.
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J4
Rexroad, C.E., Jr. and L.E. Casida. 1976. Ovarian follicular atresia and follicular estradiol-176 after unilateral ovariectomy in pregnant gilts. J. Anim. Sci. 43:802.
Robertson, H.A., and A.M. Rakha. 1965. Time of onset of oestrus in the ewe. J. Reprod. Fertil. 10:271.
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1967. Studies on the mechanisms controlling ovarian acPh.D. Thesis. University of Wisconsin, Library, Madison.
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Welschen, R. and J. Dullaart. 1974. Serum concentrations of FSH and LH after unilateral ovariectomy in the adult rat. J. Endocrinol. 6 J: 421.
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APPENDIX
35
APPENDIX TABLE 1. Al'rALYSIS OF VARIANCE TABLE FOR AGE AT FinST ESTRUS
Source of Variation
Treatment
Error
Degrees of ?reedom
4
20
~obability of obtaining a greater F value.
Mean Square
JJ16.J O.JO
2512.2
36
37
APPENDIX 2. ANALYSIS OF VARIANCE FOR THE LENGTH OF THE CONTROL AND TREATMENT ESTROUS CYCLES
Degrees of Mean Source of Variation ?reedom Sq_uare P>Fa
Treatment 4 ?.?J 0.20
Cycle (Control vs Treated) 1 2.42 0.49
Treatment x Cycle 4 J.J? 0.61
5XYor 40 4.9J
~obability of obtaining a greater F value.
38
APPENDIX TABLE 3. ANALYSIS OF COVARIANCE AND ORTHOGONAL COMPARISONS FOR THE NUMBER OF CORPORA LUTEA (OVULATION RATE)
Source of Degrees of Mean Variation Freedom Square P>Fa
Regression 1 22.11 .086
Ib 1 44.52 .019
IIb 1 74.20 .004
IIIb 1 1.80 .611
Tlb 1 0.04 .939
Error 19 6.71
~obability of obtaining a greater F value.
bSee table 4 for explanation of each of these orthogonal comparisons.
39
APPENDIX TA3L2 4. ANALYSIS OF VARIANCE FOR NUI1BER OF l1EDI1]}1 AND LARGE FOLLICLES AND TOTAL NUMBER OF FOLLICLES
Mean sguare Source of Degrees of Medium Large Total Number 'lariat ion Freedom ?ollicles P>Fa Follicles P>Fa of Follicles P>Fa
Treatment 3 351.47 .0001 42.66 .0001 160.99 .007
Error 15 24.40 2.98 26.77
~robability of obtaining a greater F value.
40
APPENDIX TABLE 5. CHI-SQUARE ANALYSIS FOR TIME OF DAY OF ONSET OF ESTRUS
2.:? <. 025
Observed Expected
x2 = 8.715a 2
0600
23 14
Time of day 1800
10 14
2400
9 14
