The effect of feed restriction on belly nosing behaviour in weaned

The effect of feed restriction on belly nosing

behaviour in weaned piglets

Andrea Bruni, V. Margaret Quinton, Tina M. Widowski *

Department of Animal and Poultry Science, University of Guelph, Guelph, Ont. N1G2W1, Canada

Accepted 2 March 2007

Available online 16 May 2007

Abstract

Belly nosing is an abnormal behaviour pattern most commonly seen in early-weaned piglets. Because

belly nosing resembles massaging the sow’s udder, it has been suggested that the behaviour is redirected

suckling and may be associated with hunger or feeding motivation. The objective of this study was to

determine the effect of feed restriction on the behaviour of newly weaned piglets. Eight groups of four

piglets were fed ad libitum during weeks 1, 2 and 3 post-weaning (control), while treatment piglets (eight

groups of four) were fed ad libitum during weeks 1 and 3, and feed restricted during week 2. During

restriction, ad libitum intake from the previous day was determined from control groups (voluntary intake of

1.9 times maintenance energy requirement), averaged, and treatment piglets were provided with 65% of this

amount (1.2 times maintenance energy requirement). While both groups continued to gain weight during the

restriction period, weight gain was significantly lower for restricted piglets compared to controls (P < 0.05).

Behaviour was observed on days 5, 7, 9, 12, 14, 17, and 20 post-weaning using a 5-min scan sampling

method for 6 h/day. During the period of restriction, treatment piglets spent less time at the feeder

(5.3 � 0.9%; controls, 8.3 � 0.6%, P < 0.05) and more time nosing and chewing at the pen (4.1 � 1.0%;

controls 1.4 � 0.4%, P < 0.05) compared to controls. Mean percentage of time spent belly nosing was not

statistically different (3.5 � 0.89%; controls 2.1 � 0.53%, P = 0.13), but the variation among piglets was

significantly greater in treatment groups (P < 0.05) during the restriction period. During the post-restriction

period, treatment piglets engaged in significantly more belly nosing behaviour (1.8 � 0.6%; controls,

0.5 � 0.2%, P < 0.05), while nosing and chewing at the pen was similar between the two groups. Feed

restriction stimulated foraging-type behaviour directed at the pen during the period of restriction, and

increased and altered the time course for belly nosing, but it did not elicit belly nosing in all pigs. Individual

differences in response to feed restriction suggest that there is a causal relationship between low feed intake

and belly nosing, but only in piglets with a predisposition for the behaviour.

# 2007 Elsevier B.V. All rights reserved.

Keywords: Piglet behaviour; Belly nosing; Feed restriction; Hunger

www.elsevier.com/locate/applanim

Applied Animal Behaviour Science 110 (2008) 203–215

* Corresponding author. Tel.: +1 519 824 4120x52408; fax: +1 519 836 9873.

E-mail address: [email protected] (T.M. Widowski).

0168-1591/$ – see front matter # 2007 Elsevier B.V. All rights reserved.

doi:10.1016/j.applanim.2007.03.016

mailto:[email protected]

http://dx.doi.org/10.1016/j.applanim.2007.03.016

1. Introduction

Under natural rearing conditions, weaning is a gradual process that involves the transition

from relying solely on sow’s milk to complete reliance of nourishment on solid food while sows

and piglets remain in contact for an extended period of time (Newberry and Wood-Gush, 1985;

Jensen and Recen, 1989; Jensen, 1995). During this process piglets go through three phases:

exclusively suckling, a period of both suckling and independent ingestion as the sow initiates

fewer nursings and terminates more (Jensen and Recen, 1989; Jensen, 1995), and finally,

exclusively independent ingestion. Early weaning in intensive rearing systems involves an abrupt

switch from suckling to feeding, and the absence of the gradual nature of this transition in diet

results in low voluntary feed intake and reduced performance referred to as post-weaning ‘growth

check’ (Pluske et al., 1995; Le Dividich and Seve, 2001). Abrupt and early weaning also results in

the development of abnormal behaviour, such as belly-nosing (see review by Widowski et al.,

2008). Belly nosing follows a consistent time course; it typically develops around 3–5 days after

weaning, peaks around 2 weeks after weaning and then declines (Blackshaw, 1981; Gonyou

et al., 1998; see review by Widowski et al., 2008).

It is well established that both a delay in initiating feeding and the performance of belly nosing

are more prevalent in piglets weaned at an earlier age (Metz and Gonyou, 1990; Gonyou et al.,

1998; Worobec et al., 1999). It has also been recognized that there is a great deal of individual

variation in the amount of time piglets spend belly nosing (Straw and Bartlett, 2001; Li and

Gonyou, 2002). Since belly nosing behaviour clearly resembles the motor patterns involved in

massaging the sow’s udder during the appetitive and post-consummatory phases of nursing, it has

been suggested that it is redirected suckling (Metz and Gonyou, 1990; Dybkjær, 1992; also see

review by Widowski et al., 2008) and might be associated with hunger or feeding motivation

(Gardner et al., 2001; Li and Gonyou, 2002). However, studies that have examined the effect of

different aspects of feeding on the performance of belly nosing behaviour indicate that the

association is not straightforward.

Neither offering a nutritionally complex diet versus a simple diet (Weary et al., 1999) nor

providing piglets with a low quality versus high quality diet (in terms of protein) (Gardner et al.,

2001) affected the performance of belly nosing behaviour, even though piglets had lower intakes

and grew more slowly on the poor quality diets. Additionally, examination of the temporal

association between the performance of belly nosing and feeding, through sequential analysis,

revealed no relationship between these two behaviour patterns (Li and Gonyou, 2002). However,

belly nosing has been demonstrated to be associated with some aspects of ingestive behaviour.

Feeding piglets a mash/liquid diet increases early dry matter intake and results in significantly

less time belly nosing compared to piglets fed a standard pelleted diet (Rau, 2002; Brooks et al.,

2001; Orgeur et al., 2003). Providing piglets water from a bowl type drinker as opposed to a

nipple drinker increased feed intake during the first 48 h after weaning and also reduced the

performance of belly nosing (Torrey and Widowski, 2004).

Belly nosing has also been found to be associated with poor growth rates (Fraser, 1978; Straw

and Bartlett, 2001; Torrey and Widowski, 2006). Several studies have reported a negative

correlation between belly nosing behaviour and feeding; those individuals that perform more

belly nosing spend less time at the feeder (Li and Gonyou, 2002; Bruni, 2004; Torrey and

Widowski, 2006). This raises the question: do piglets that develop belly nosing simply have less

time available for other activities and consequently spend less time eating, or is there a causal

relationship between low feed intake and belly nosing? One way to answer this question is to

determine whether an imposed feed restriction can elicit belly nosing behaviour either by causing

A. Bruni et al. / Applied Animal Behaviour Science 110 (2008) 203–215204

hunger (the psychological state associated with low nutrient levels) or through reduced growth

(the metabolic consequences of low nutrient status). Therefore, the aim of this study was to

determine the effect imposed feed restriction, on the performance of oral–nasal behaviour in

newly weaned piglets. We hypothesized that if low feed intake is causally related to belly nosing,

piglets subjected to feed restriction would perform more of the behaviour.

2. Materials and methods

The University of Guelph Animal Care Committee approved all procedures of this study.

2.1. Animals and housing

A total of 64 Yorkshire piglets (16 in each of 4 trials), from the Arkell Swine Research facility were used

in this study. For each separate trial, sixteen piglets (with an average weaning weight of 6.40 � 0.08 kg),

from three or four different litters were selected based on weight (between 5.0 and 7.5 kg) and gender

(approximately an equal distribution of gilts and barrows). Piglets were weaned between 18 and 22 days of

age, individually marked, weighed and divided randomly into groups of four.

At weaning, piglets were moved from standard farrowing crates to an on-site nursery room. All groups of

piglets were mixed equally, balancing for weight and gender. The room contained four separate raised deck

pens, each having a dimension of 1.13 m � 1.13 m and a plastic coated expanded metal open mesh floor.

Each pen was equipped with a single nipple drinker, a four-holed stainless steel feeder, and a single heating

pad. Heating pads were controlled manually, monitored daily and adjusted as required to maintain pig

comfort.

Daily ambient temperature averaged approximately 28.36 � 2.6 8C. Throughout the experiment, piglets

were provided with standard phase II feed (University of Guelph, Arkell Feed Mill, Guelph, Ont., Canada;

Table 1) and were given free access to water from bite-style nipple drinkers.

2.2. Experimental design

Two pens of four pigs within each of the four trials were randomly assigned to treatment while the other

two served as controls. Thus, the experiment was a randomized complete block design with subsampling

(Steel et al., 1997), which consisted of two pens per treatment per trial (total of eight replicates). Piglets

assigned to the control group were fed ad libitum for the duration of the experiment (weeks 1, 2 and 3 post-

weaning), while treatment piglets were exposed to a regimen that consisted of a weekly alternation of ad

libitum (weeks 1 and 3) and restricted feeding (week 2 post-weaning). Essentially, the experiment consisted

of three periods that included: the pre-restriction period (days 1–7 of the experiment), the restriction period

(days 8–14) and the post-restriction period (days 15–21).

During the restriction period (second week post-weaning), feed from control groups was weighed back

and intake from the previous day was determined on a daily basis. The amount consumed by each of the

control groups was averaged, and treatment piglets were provided with 65% of this amount. For ethical

reasons, the level of restriction applied in this experiment was chosen based on maintenance energy

requirements for piglets this age such that feeding levels for restricted piglets would be well below voluntary

feed intake, but they would not lose weight.

2.3. Data collection

2.3.1. Feed intake and growth

Piglets were fed at 09:00 h each morning. This daily process consisted of weighing back feed, removing

stale feed, and adding a weighed out amount of fresh feed to feeders. Feed spillage was minimal and was not

accounted for in estimates of intake. Feed intake was determined on a per pen basis.

A. Bruni et al. / Applied Animal Behaviour Science 110 (2008) 203–215 205

Piglets were individually weighed at weaning and again on days 8, 15 and 21 post-weaning. Weekly

weight gain was determined for each piglet.

2.3.2. Behaviour

Piglets were video taped continuously for a 24-h period on days 5, 7, 9, 12, 14, 15, 17 and 20 post-

weaning. Cameras (Panasonic WV-BP130, BP140 CCTV) were positioned on tripods, which were mounted

to one side of each pen. Cameras were connected to a recording system that consisted of a monitor, a

multiplexer (Simplex Multiplexer) and a time-lapse VCR (Panasonic AG-6730/6040), which recorded at a

speed of 24 h. This allowed all four pens to be viewed at once. For behavioural observations, data was

collected on days 5 and 7 when belly nosing characteristically first develops, days 9, 12 and 14 when belly

nosing usually peaks and days 17 and 20 when belly nosing is most often observed to decline.

Behavioural data were collected using a scan sampling method every 5 min for 6 h per day (Gardner

et al., 2001). Behaviour was sampled during two periods: 06:00–09:00 h, immediately before feeding when

feeders were empty and piglets were presumably hungry, and 14:00–17:00 h, after restricted piglets had

several hours to eat but usually still had feed available in their feeders. Each piglet was individually marked

and its behaviour was recorded in order to obtain an estimate of its time budget. Behaviour was allocated to

one of eight mutually exclusive behavioural categories listed in Table 2.


Table 1

Nutrient levels and ingredient composition (%) of Piglet Starter II diet

Ingredient Percentage in diet

Corn 32.3

Barley 8.0

Wheat 20.0

Soybean meal 22.0

Fish meal 5.0

Whey 8.0

Fat 2.0

Lysine–HCl, 79% 0.30

Methionine 0.01

Threonine 0.12

Dicalcium phosphate 0.60

Limestone 0.70

Iodized salt 0.30

Vitamin premixa 0.50

Mineral premixb 0.10

Tylosin premixc 0.10

Nutritive value (calculated)

DE (kcal/kg) 3450

Crude protein (%) 19.83

Calcium (%) 0.82

Phosphorus (%) 0.65

Available phosphorus (%) 0.62

Values are presented on an as-fed basis. This diet was available in crumble form and was manufactured at University of

Guelph, Arkell Feed Mill, Guelph, Ont., Canada.a Vitamin premix supplied the following per kg of feed: vitamin A, 10,000 IU; cholecalciferol, 1000 IU; DL-a-

tocopherol acetate, 56 IU; menadione, 2.5 mg; choline, 500 mg; pantothenic acid, 15 mg; riboflavin, 5 mg; folic acid,

2 mg; thiamine, 1.5 mg; pryoxidine, 1.5 mg; biotin, 0.20 mg; vitamin B12, 0.025 mg.b Mineral premix supplied the following per kg feed: Cu, 15 mg; Zn, 104 mg; Fe, 100 mg; Mn 19 mg.c Tylosin premix supplied 22 mg/kg of complete feed.

2.4. Statistical analysis

All statistical analyses were conducted using the SAS statistical software program (SAS Inst., Inc., Cary,

NC). The Proc Mixed procedure was used to determine any differences in feed intake, weight gain and

behavioural means between treatment and control groups over each period. The arcsine of the square root

transformation was used to transform data recorded as proportions when necessary. Linear and quadratic

orthogonal polynomial contrasts across the 3 days in the restriction period and linear orthogonal polynomial

contrasts (differences) across the 2 days in the post-restriction period were analyzed in order to compare

trends across days in the treated and control pens (Kuehl, 1994). Pre-restriction values were used as

covariates for analysis of both the restriction and post-restriction periods in order to eliminate any

differences in behaviour between the two groups before treatment was applied.

Residual plots indicated the variance within pens differed between the treated and control pens for some

of the behavioural traits recorded, particularly belly nosing. Two models were fit to the data set. The

homogenous model considered the within-pen variance to be the same across treatments, while the

heterogeneous model structure considered the within-pen variance different across treatments. The log

likelihood ratio test was employed to determine if the heterogeneous model was a significantly better fit to

the data set, and to examine any differences in variance due to treatment (Steel et al., 1997). The

heterogeneous model was a significantly better fit for belly nosing behaviour, while the homogenous

model was a better fit for all other behaviour patterns recorded.

Behaviour data were averaged over the sampling days for each piglet during week 2 and for all 3 weeks

of the trial combined. Pearsons correlations (PROC CORR) were performed on data from individual piglets

to identify relationships between weight gain and average time spent belly nosing and between time at the

feeder and belly nosing during the restriction period and overall. Data from one piglet in the control group

was removed from the data set due to illness.

3. Results

3.1. Feed intake and growth performance

Average weaning weight was 6.3 � 0.2 kg for control piglets and 6.5 � 0.1 kg for restricted

(P > 0.10). During the first week post-weaning (pre-restriction period) there were no differences

in weight gain (P = 0.87) or feed intake (P = 0.93) between treatment and control groups

(Table 3). During the restriction period, when treatment piglets were provided with only 65% of

ad libitum intake, weight gain of feed-restricted piglets was significantly lower (P = 0.0001) as


Table 2

Observed mutually exclusive behaviour patterns and their definitions

Behaviour Definition

Belly nosing A distinctive, rhythmic up-and-down movement of a piglet’s snout against

the belly of another piglet (Fraser, 1978)

Nosing/chewing

pen-mates

Oral–nasal contact with the body of a pen-mate (distinct from belly

nosing behaviour) (Fraser, 1978)

Nosing/chewing pen Oral–nasal contact with any part of the pen (including floor and side bars)

Fighting Pushing, head-thrusting or chasing directed towards a pen-mate

At feeder Head positioned in or above feeder

Drinking Snout in contact with nipple drinker

Resting Lateral and sternal recumbancy when engaged in no other activity

Active Includes sitting, standing, walking and transitional movements between

behaviour categories

compared to control piglets (Table 3). During the post-restriction period, while feed intake was

similar between treatment and control groups (P = 0.08), treatment piglets had a higher weight

gain (P = 0.0013) compared to control piglets (Table 3). Overall, both weight gain and feed

intake showed significant quadratic trends, indicating that, as expected, their change over time

was affected by treatment (P < 0.05).

3.2. Behaviour

During the pre-restriction period, there were no significant differences in any measured

behaviour pattern between treatment and control piglets.

During the restriction period, treatment had a significant effect on several behaviour patterns

during the observation hours. Feed-restricted piglets spent significantly less time at the feeder

(P < 0.01), more time nosing and chewing the pen (P < 0.02), were more active (P < 0.03) and

had a tendency to spend less time resting (P < 0.07) compared to control piglets (Table 4).

However, percentage of time spent belly nosing (P = 0.13), nosing and chewing the ears and tails

of pen-mates (P = 0.22), fighting (P = 0.52) and drinking (P = 0.16) were not different between

the restricted and control pens (Table 4). Although treatment did not significantly affect mean

percentage of time spent belly nosing, treatment did affect the individual variation in the


Table 3

The effect of feed restriction on weight gain and feed intake (mean � S.E.M.) during each week of the study

Variable Treatment Control

Weight gain (kg/pig)

Pre-restriction 0.48 � 0.14 0.50 � 0.07

Restriction 0.64 � 0.07a 1.80 � 0.14

Post-restriction 3.12 � 1.47a 2.65 � 1.12

Feed intake (kg/pig)

Pre-restriction 0.80 � 0.08 0.70 � 0.04

Restriction 1.17 � 0.05a 1.82 � 0.08

Post-restriction 3.56 � 0.15 3.85 � 0.10

a Means within a row are significantly different (P < 0.05).

Table 4

The effect of feed restriction on the mean of each behaviour pattern during restriction and post-restriction periods

(mean � S.E.M.)

Behaviour Restriction period (mean % of time engaged

in each behaviour pattern)

Post-restriction period (mean % of time

engaged in each behaviour pattern)

Treatment Control P-value Treatment Control P-value

Belly nosing 3.52 � 0.89 2.12 � 0.53 0.13 1.80 � 0.57 0.49 � 0.20 0.003

Nosing/chewing

pen-mates

2.01 � 0.46 1.28 � 0.23 0.22 2.14 � 0.44 1.43 � 0.16 0.31

Nosing/chewing pen 4.11 � 1.06 1.42 � 0.38 0.01 2.48 � 0.65 1.90 � 0.38 0.66

At feeder 5.27 � 0.96 8.34 � 0.66 0.001 9.31 � 0.50 9.29 � 0.83 0.99

Active 19.0 � 2.34 12.67 � 1.16 0.02 14.41 � 1.49 12.53 � 1.07 0.17

Resting 65.47 � 3.84 73.31 � 1.40 0.07 68.56 � 2.73 73.11 � 1.51 0.03

Fighting 0.03 � 0.03 0.06 � 0.04 0.52 0.20 � 0.10 0.08 � 0.05 0.29

Drinking 0.55 � 0.08 0.78 � 0.13 0.16 1.12 � 0.20 1.14 � 0.21 0.26

performance of the behaviour. Percentage of time spent belly nosing ranged from 0 to 13.5% for

control piglets and from 0 to 17.6% for restricted. Two of the 31 control piglets and 3 out of the 32

restricted piglets were never observed belly nosing during the restriction period. The variance of

belly nosing within pens was greater for feed-restricted piglets compared to control piglets (log

likelihood ratio; P < 0.05). There was no evidence that the variation within pens differed

between the treatments for any other behaviour recorded (log likelihood ratio; P > 0.05).

Orthogonal polynomial contrasts across days indicated significantly different quadratic trends in

time spent at the feeder (Fig. 1), nosing and chewing the pen (Fig. 2) and piglet activity (Fig. 3)

but not belly nosing (Fig. 4), and significantly different linear trends for lying (Fig. 5) between

treatment and control piglets (P < 0.05).


Fig. 1. Mean (�S.E.M.) percentage of time piglets spent at the feeder (difference between treatments: during restriction

P < 0.05; linear P > 0.05; quadratic P < 0.05; during post-restriction P > 0.05; linear P > 0.05).

Fig. 2. Mean (�S.E.M.) percentage of time piglets spent nosing and chewing the pen (difference between treatments:

during restriction P < 0.05; linear P > 0.05; quadratic P < 0.05; during post-restriction P > 0.05; linear P > 0.05).

During the post-restriction period, when all piglets were once again fed to appetite, treatment

piglets spent significantly more time belly nosing (P < 0.01) and spent less time resting

(P < 0.03) compared to control piglets (Table 4). During this period there were no significant

differences in nosing and chewing the ears and tails of pen-mates, nosing and chewing the pen,

time spent at the feeder, piglet activity, fighting or drinking (Table 4). Orthogonal polynomial

contrasts across days indicted no significant differences in the change in behaviour over time

between treatment and control groups during this period (P > 0.05).


Fig. 3. Mean (�S.E.M.) percentage of time piglets spent in activity (difference between treatments: during restriction

P < 0.05; linear P > 0.05; quadratic P < 0.05; during post-restriction P > 0.05; linear P > 0.05).

Fig. 4. Mean (�S.E.M.) percentage of time piglets spent belly nosing (difference between treatments: during restriction

P > 0.05; linear P > 0.05; quadratic P > 0.05; during post-restriction P < 0.05; linear P > 0.05; variance analysis during

restriction: log likelihood ratio P < 0.05).

Pearsons correlations indicated no relationship between weaning weight and belly nosing

during the restriction period or overall (Table 5). However, there were several significant negative

correlations between weight gain and belly nosing. Weight gain during week 2 (restriction

period) was significantly negatively correlated with belly nosing in week 2 when data for all

piglets were combined (P < 0.04). Total weight gain (for the entire trial) was negatively

correlated with overall belly nosing for control pigs (P < 0.01) and for all pigs combined

(P < 0.01) and tended to be related for restricted pigs (P < 0.10). Time spent at the feeder was

not correlated with belly nosing when piglets in each treatment were analyzed separately, but


Fig. 5. Mean (�S.E.M.) percentage of time piglets spent resting (difference between treatments: during restriction

P > 0.05; linear P > 0.05; quadratic P > 0.05; during post-restriction P < 0.05; linear P > 0.05).

Table 5

Pearsons correlation coefficients between belly nosing and growth and belly nosing and feeding behaviour during the

week of feed restriction (week 2) and for all 3 weeks combined

Treatment Weaning

weight

Weight

gain week 2

Weight gain

overall

At feeder

week 2

At feeder

overall

Control

(N = 31)

Belly nosing

week 2

�0.04,

P = 0.84

�0.22,

P = 0.24

�0.29,

P = 0.11

Belly nosing

overall

�0.03,

P = 0.85

�0.49,

P < 0.01

�0.22,

P = 0.12

Restricted

(N = 32)

Belly nosing

week 2

�0.18,

P = 0.32

�0.25,

P = 0.17

�0.14,

P > 0.45

Belly nosing

overall

�0.23,

P = 0.20

�0.30,

P = 0.09

�0.17,

P > 0.35

All piglets

(N = 63)

Belly nosing

week 2

�0.09,

P > 0.45

�0.26,

P < 0.04

�0.25,

P = 0.05

Belly nosing

overall

�0.12,

P > 0.34

�0.39,

P < 0.002

�0.21,

P = 0.09

there was a negative relationship between time spent at the feeder in week 2 and belly nosing in

week 2 (P = 0.05) and between time at the feeder and belly nosing overall (P = 0.09).

4. Discussion

Our experiment was designed to investigate a causal relationship between low feed intake

and belly nosing behaviour. Our results suggest that belly nosing was affected by feed

restriction, but there were individual differences in the response. Large individual variation in

the amount of time piglets spend belly nosing has been reported in several studies; some

animals are never observed to perform the behaviour, while others belly nose at relatively high

levels (Straw and Bartlett, 2001; Li and Gonyou, 2002). Piglets with a predisposition to belly

nose direct more post-weaning activity at the bodies of pen-mates while those that perform less

belly nosing direct more oral activity at floors and feeders (Torrey and Widowski, 2006). In the

current study, feed restriction appeared to amplify those individual differences in belly nosing.

Although averages for time spent belly nosing were not statistically different, variance within

pen was greater in feed-restricted piglets compared to those fed ad libitum during the period of

feed restriction, and this was the only behaviour pattern for which this effect on variance was

found. It is possible that reduced feed intake (or hunger) may have exacerbated the

performance of belly nosing in those individuals that already had developed this behaviour

during the first week, but did not elicit it in pigs that were not previously exhibiting the

behaviour. This is supported by the observation that three of the 32 piglets in the restricted

treatment (and 2 of the 31 controls) were never observed belly nosing during the observations

in the period of restriction and one of the restricted pigs was never observed to belly nose on

any day.

Some of the increased variation and lack of statistical difference in belly nosing behaviour

during the restriction period may have been due to the increase in activity levels also observed

during that time. Stimulating activity and time spent nosing and chewing the pen may have

reduced the opportunities or number of recipient piglets available for belly nosing, since most

occurrences of this behaviour are targeted at individuals that are less active (Gonyou et al., 1998;

Straw and Bartlett, 2001). The small sample size combined with large variation may also have

contributed to the lack of statistical significance. The relatively small group sizes of only four

piglets per pen could also have resulted in few or no pigs with a predisposition to belly nose being

allotted to a pen simply by chance, however, belly nosing was observed in at least three piglets in

each of the pens.

The young pig has a tremendous biological growth potential but actual growth rate may be

limited by feed intake after weaning (Le Dividich and Seve, 2001). After weaning, piglets are

known to undergo a short period of low voluntary feed and consume amounts below maintenance

energy requirements (Le Dividich and Seve, 2001). In the second week post-weaning, piglets

weaned at approximately 3 weeks of age gradually increase feed intake and reach a plateau in

metabolizable energy intake per unit of body weight between 14 and 21 days after weaning (Le

Dividich and Seve, 2001). The feed restriction period in our study was introduced in the second

week post-weaning after most piglets had presumably established feeding so that reduced feed

intake was imposed rather than voluntary. Control piglets showed the expected increase in

average growth rates and feed intakes during the second week after weaning. Feed restriction

during this time slowed growth rates, also as expected. During the post-restriction period, when

treatment piglets were once again fed to appetite, both groups consumed feed at similar rates but

previously restricted piglets had higher weight gains.


Individual piglets that exhibit belly nosing typically have poor growth rates (Fraser, 1978;

Straw and Bartlett, 2001; Torrey and Widowski, 2006) and this relationship was also observed in

the control piglets relying on voluntary intake in this study. Overall weight gain only tended to be

related to belly nosing in treatment pigs, probably because even those piglets that did not perform

very much belly nosing grew more slowly. The relationship between time at the feeder and belly

nosing was only significant when data from all piglets were analyzed together, probably because

of the small sample size. Also, there no relationship between time at the feeder and weight gain

(data not shown). Although time spent at the feeder has been shown to be related to feed intake in

piglets weaned at 28 days or older (Dybkjær, personal communication) a lack of correspondence

between time at the feeder and feed intakes has been observed in several studies involving pigs

weaned at younger ages (Gardner et al., 2001; McGlone and Anderson, 2002; Torrey and

Widowski, 2004). The lack of association between weaning weight and belly nosing is consistent

with what has been observed in other studies (Straw and Bartlett, 2001; also see review by

Widowski, et al., this volume).

The time course for belly nosing in the control group was consistent with what has been

reported in the literature (Gonyou et al., 1998; Torrey and Widowski, 2004). Its onset was

obvious by day 7 post-weaning, peaked during the second week, and then declined by the end of

week 3. However, the time course was somewhat different for treatment piglets. Rather than

steadily declining after peak levels on day 9, the percentage of time spent belly nosing remained

elevated into the post-restriction period resulting in significantly higher belly nosing in restricted

pigs compared to controls in the final week of the trial. This suggests that the effects of restricted

feed on belly nosing are not due to hunger per se, but rather through a discrepancy between

growth and growth potential since there is a lag between time of nutrient intake and weight gain

(Prince et al., 1983; Dunshea, 2003).

Feed restriction affected other aspects of the piglets’ behaviour in several ways. Some behaviour

responses appeared to directly correspond to the period of reduced feed availability while others

only appeared over the course of the week. Feed restriction reduced the amount of time piglets spent

at the feeder, and increased the proportion of time piglets engaged in pen-directed nosing and

chewing behaviour throughout the restriction period. Reduction in time spent at the feeder can be

attributed to the fact that feeders were empty about half of the observation time. Once piglets were

given their ration for the day, they consumed it quickly and did not spend any more time than

needed, at the feeder. However, they did spend more time nosing and chewing the pen, likely caused

by hunger, which elevated feeding motivation and in turn, increased the performance of foraging

related behaviour. Day et al. (1995) found that older pigs feed restricted by 20% of ad libitum intake,

showed an increase in time spent rooting substrate. In our study, nosing and chewing the pen could

be considered a form of rooting behaviour, representing appetitive foraging resulting from an

increase in feeding motivation. Since piglets were hungry, they may have been actively searching

the pen for food. An alternative hypothesis for the increase in pen-directed nosing and chewing

behaviour observed in treatment piglets may be increased frustration as a result of prevention from

engaging in feeding behaviour. Under conditions that restrict the performance of normal feeding

behaviour, animals may direct the behaviour towards alternative stimuli (Lawrence et al., 1993).

Lewis (1999) suggested that frustration associated with the inability of pigs to engage in feeding to

satisfy their hunger, rather than hunger itself, leads to increased oral activity. It has been suggested

that belly nosing may be a behavioural indicator of stress (Dybkjær, 1992; also see Widowski et al.,

2008) and it might be argued that the changes in belly nosing observed in restricted pigs in this

experiment could be caused by the ‘stress’ of hunger or reduced feed intake rather than a more

direct effect of nutrient or growth status. However, belly nosing remained significantly higher in


restricted pigs during the early post-restriction period when pigs were again eating to appetite and

time at the feeder and nosing the pen were similar for control and treatment pigs.

During the period of restriction, feed-restricted piglets became more active and rested less than

ad libitum fed piglets but these differences only became apparent over time. Examination of diurnal

feeding patterns in swine has indicated that meal patterns typically show a peak in the morning, one

or two subsequent peaks later in the day, and modest intake during the night (Fraser, 1984). In our

experiment, treatment piglets were fed once a day (09:00 h). Observations were conducted during

the 3 h prior to feeding when feeders were usually empty and early in the afternoon when food was

usually available. Piglets may have learned to anticipate feeding time, which altered their activity

patterns over the course of theweek. Similar trends in behaviour were found in a study conducted by

Hammel and Hurnik (1987) who found that meal-fed gilts and cattle rapidly learned the feeding

schedule and were more active (in terms of time spent walking and standing) and spent less time

resting compared to ad libitum fed animals. Day et al. (1995) also found that pigs restricted by 20%

of ad libitum intake spent much less time lying compared to controls but this was observed during

tests for foraging motivation when the pigs were outside of their home pens.

During the period of feed restriction, treatment did not have an effect on nosing and chewing

the ears and tails of pen-mates or fighting. Increased restlessness is often accompanied by an

increase in oral activity directed at pen-mates (Fraser, 1987). However, feed restriction in our

study did not have an influence on nosing and chewing the ears and tails of pen-mates, possibly

because piglets may have been more motivated to engage in foraging related behaviour directed

at the pen, rather than nose and chew their pen-mates. It was surprising that feed restriction did

not have an effect on aggressive behaviour. This may have been because there was little

competition at the feeder since each pen was equipped with a four-placed feeder, allowing all

four pigs to feed simultaneously when feed was available.

In summary, piglets subjected to feed restriction during the second week post-weaning

reduced resting and increased general activity and nosing/chewing the pen compared to piglets

fed ad libitum. Feed restriction increased the variation in and altered the time course for belly

nosing, and increased the occurrence of belly nosing in the week after feed restriction, but it did

not elicit the behaviour in all pigs that were feed restricted. This suggests that there is a causal

relationship between low feed intake and belly nosing, but only in individual piglets with a

predisposition for the behaviour.

Acknowledgements

This research was funded by grants from the Natural Sciences and Engineering Research

Council (NSERC) and the Ontario Ministry of Agriculture and Food. We thank the staff of the

Arkell Swine Research Station for their assistance. Special thanks go to Emily Toth for her many

hours of service in the barn.

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The effect of feed restriction on belly nosing behaviour in weaned