The effect of feed restriction on belly nosing behaviour in weaned piglets

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1 Applied Animal Behaviour Science 110 (2008) 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 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 ( %; controls, %, P < 0.05) and more time nosing and chewing at the pen ( %; controls %, P < 0.05) compared to controls. Mean percentage of time spent belly nosing was not statistically different ( %; controls %, 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 ( %; controls, %, 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; ; Feed restriction; Hunger * Corresponding author. Tel.: x52408; fax: address: twidowsk@uoguelph.ca (T.M. Widowski) /$ see front matter # 2007 Elsevier B.V. All rights reserved. doi: /j.applanim

2 204 A. Bruni et al. / Applied Animal Behaviour Science 110 (2008) 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 Recén, 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 Recén, 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 Séve, 2001). Abrupt and early weaning also results in the development of abnormal behaviour, such as belly-nosing (see review by Widowski et al., 2008). 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). 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

3 A. Bruni et al. / Applied Animal Behaviour Science 110 (2008) 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 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 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 C. 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 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 postweaning), 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 Data collection 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.

4 206 A. Bruni et al. / Applied Animal Behaviour Science 110 (2008) 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 premix a 0.50 Mineral premix b 0.10 Tylosin premix c 0.10 Nutritive value (calculated) DE (kcal/kg) 3450 Crude protein (%) 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-atocopherol 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, 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. Piglets were individually weighed at weaning and again on days 8, 15 and 21 post-weaning. Weekly weight gain was determined for each piglet Behaviour Piglets were video taped continuously for a 24-h period on days 5, 7, 9, 12, 14, 15, 17 and 20 postweaning. 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.

5 A. Bruni et al. / Applied Animal Behaviour Science 110 (2008) Table 2 Observed mutually exclusive behaviour patterns and their definitions Behaviour Nosing/chewing pen-mates Nosing/chewing pen Fighting At feeder Drinking Resting Active Definition A distinctive, rhythmic up-and-down movement of a piglet s snout against the belly of another piglet (Fraser, 1978) Oral nasal contact with the body of a pen-mate (distinct from belly nosing behaviour) (Fraser, 1978) Oral nasal contact with any part of the pen (including floor and side bars) Pushing, head-thrusting or chasing directed towards a pen-mate Head positioned in or above feeder Snout in contact with nipple drinker Lateral and sternal recumbancy when engaged in no other activity Includes sitting, standing, walking and transitional movements between behaviour categories 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 kg for control piglets and 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 = ) as

6 208 A. Bruni et al. / Applied Animal Behaviour Science 110 (2008) 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 Restriction a Post-restriction a Feed intake (kg/pig) Pre-restriction Restriction a Post-restriction a Means within a row are significantly different (P < 0.05). 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 = ) 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) 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 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 Nosing/chewing pen-mates Nosing/chewing pen At feeder Active Resting Fighting Drinking

7 A. Bruni et al. / Applied Animal Behaviour Science 110 (2008) 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). 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. 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).

8 210 A. Bruni et al. / Applied Animal Behaviour Science 110 (2008) 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). 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. 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).

9 A. Bruni et al. / Applied Animal Behaviour Science 110 (2008) 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). 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 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) Restricted (N = 32) All piglets (N = 63) week 2 overall week 2 overall week 2 overall 0.04, P = , P = , P = , P = , P > , P > , P = , P = , P < , P < , P = , P < , P = , P > , P = , P = , P > , P = 0.09

10 212 A. Bruni et al. / Applied Animal Behaviour Science 110 (2008) 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 Séve, 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 Séve, 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 Séve, 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.

11 A. Bruni et al. / Applied Animal Behaviour Science 110 (2008) 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

12 214 A. Bruni et al. / Applied Animal Behaviour Science 110 (2008) 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. References Blackshaw, J.K., Some behavioural deviations in weaned domestic pigs: persistent inguinal nose thrusting, and tail and ear biting. Anim. Prod. 33, Brooks, P.H., Moran, C.A., Beal, J.D., Demeckova, V., Campbell, A., Liquid feeding for the young piglet. In: Varley, M.A., Wiseman, J. (Eds.), The Weaner Pig: Nutrition and Management. CABI Publishing, Wallingford, Oxon, UK, pp Bruni, A., Investigations into the effect of cold draft and feed restriction on the behaviour of newly weaned piglets. M.Sc. Thesis, University of Guelph, Guelph, Ontario.

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