David Fraser

Within-Litter Birth Weight Variation in the Domestic Pig and its Relation to Pre-Weaning Survival, Weight Gain, and Variation in Weaning Weights

Abstract To determine the relationship between within-litter birth weight variation and pre-weaning survival and weight gain, and to provide practical guidance on fostering low-birth-weight piglets, we analyzed piglet survival and weight gain in litters of piglets from 52 sows followed through eight consecutive parities. Litters with high variation in birth weight had more deaths, especially if the litter’s mean birth weight was low. High variation in birth weight was also associated with high variation in weaning weight, but was not significantly related to mean weaning weight. Piglets with birth weights well below the range of most of the litter (‘low-birth-weight piglets’) were more likely to die than their litter-mates, but their weight gains were normal for their birth weight if they survived. These piglets experienced particularly low survival in larger litters and litters from sows of sixth parity or older. Litters containing low-birth-weight piglets started, on average, with more piglets born alive and had a lower pre-weaning survival (with the majority of deaths being low-birth-weight piglets), but did not wean significantly more piglets than litters without low-birth-weight piglets. The majority of litters had a negatively skewed distribution of birth weights, with more piglets well below the mean than well above it. Our data are consistent with the hypothesis that high variation in birth weight contributes to reduced survival, at least for litters of low mean birth weight, and to variable weaning weights. Our data also support the hypothesis that in terms of survival, small piglets have a competitive disadvantage compared to their heavier litter-mates, a disadvantage that is exacerbated in large litters and litters from older sows. Our data suggest that selection for increased litter size that results in more low-birth-weight piglets per litter may not be beneficial unless measures are undertaken to improve the survival of low-birth-weight piglets.

Effect of straw on the behaviour of growing pigs

Abstract The effects of straw on the behaviour of young growing pigs were studied in two experiments. In Experiment 1, groups of three pigs, aged about 7 weeks, were housed in raised decks with or without straw bedding. Time-lapse video recording showed no major differences between treatments in the amount or daily pattern of overall activity and feeding. Detailed observations showed that bedding reduced the incidence of rooting and chewing on pen-mates, but had little effect on other social activities such as mounting and aggressive biting. Experiment 2 compared groups of eight growing pigs aged about 10 weeks, housed in floor pens with or without a small amount of straw provided daily in a rack. Pigs with straw concentrated more of their daily activity into the period when straw was fresh, but the total amount of overall activity and time spent feeding were not affected. Rooting and chewing of pen-mates were the only social activities reduced by the provision of fresh straw. In these studies, where straw was not required to compensate for deficiencies such as low temperatures or hunger, the one major function of straw was to provide a stimulus and outlet for rooting and chewing, with a resulting reduction in such activities directed at pen-mates.

Animal Ethics and Animal Welfare Science: Bridging the Two Cultures

Abstract Since the 1970s, scientists studying animal welfare and philosophers writing about animal ethics have worked toward the common goal of understanding and articulating our proper relationship to animals of other species. However, the two groups approached this task using such different concepts, assumptions, and vocabulary that they functioned as two distinct “cultures” with little mutual understanding or communication. Some of the best known ethical writing created barriers for scientists because it tended (1) to focus only on the level of the individual rather than making some decisions at the level of the population, ecosystem or species, (2) to advocate single ethical principles rather than balancing conflicting principles, (3) to ignore or dismiss traditional ethics based on care, responsibility, and community with animals, (4) to seek solutions through ethical theory with little recourse to empirical knowledge, (5) to lump diverse taxonomic groups into single moral categories, and (6) to propose wholesale solutions to diverse animal use practices. Meanwhile, some of the scientists alienated the ethicists by taking the view that suffering and other subjective experiences of animals are not amenable to scientific enquiry, and by the claim that science could “measure” animal welfare as if it were a purely empirical concept. However, other (often less well known) work in animal ethics creates links with animal welfare science and looks to empirical research to help resolve animal ethics issues. Some of this work (1) expresses moral concern about animals using concepts that lend themselves to scientific analysis, (2) attaches value to traditional care for and community with animals, (3) recognizes the importance of empirical analysis for discriminating between good and bad animal use practices, and (4) sees different taxonomic groups as meriting different types and levels of ethical concern. At the same time, animal welfare science has grown more compatible with the approaches used by some ethicists. Some scientists have recognized and tried to clarify the interplay of normative and empirical elements in the assessment of animal welfare, and many are attempting to understand ethically relevant subjective experiences of animals. The increasing convergence of the scientific and philosophical approaches may lead to a more integrated field of study and to a greater awareness that neither empirical information nor ethical reflection can, by itself, answer questions about our proper relationship to animals of other species.

Consumption of solid food by suckling pigs: individual variation and relation to weight gain

Individual daily consumption of supplementary solid food (‘creep feed’) was measured from Day 10 to weaning at Day 28 for 39 piglets in four litters, and its relationship to body weight and weight gain up to Day 42 was investigated. Individual consumption was measured by combining the weight of the feed removed from the dispensers (monitored electronically) and a video image of piglet activity at the feeder. Creep feed consumption varied greatly, both between and within litters. On average, pigs began feeding on Day 12 (range Day 10–28), intake was relatively low (usually <5 g day−1) until Day 20 but increased considerably in the week before weaning, with a mean intake of 63 g day−1 (range 2–205 g day−1) during that week. Over the entire creep-feeding period, total feed consumption ranged from 13–1911 g per pig. Within litters, intake was positively correlated with birth weight (P<0.05) and the correlation with weight gains to Day 20 tended to be positive rather than negative. This suggests that greater creep feed intake was typical of the larger and more mature piglets, rather than serving as compensation for poor milk intake among the more deprived litter-mates. However, one exceptional pig began, on Day 14 after several days of weight loss, to eat more creep feed than any other piglet studied, suggesting that compensatory creep feeding can occur at a young age in exceptional cases. In a multiple regression analysis, creep feed intake accounted for 37% of the variation in weight gain in the week before weaning (P<0.001) and 7% of the variation in gain from Day 10 to weaning (P<0.01) after variation attributable to antecedent variables had been taken into account. Within-litter differences in weight gain during the 2 weeks after weaning were correlated with weight at birth and weight gain before weaning (P<0.05), but not with pre-weaning creep feed intake. Hence, creep feed intake appeared to contribute to pre-weaning gains and these in turn were correlated with post-weaning gains; however, a more direct effect of pre-weaning creep feed intake on post-weaning gain could not be detected.

Responses of piglets to early separation from the sow

Abstract Two experiments examined the effect of age and diet on behavioural responses of piglets to separation from the sow. In Experiment 1, the vocalizations of piglets were recorded during short term (10 min) isolation from the sow and litter-mates at 1, 2, 3 and 4 weeks of age. From each of 10 litters, two piglets were assigned to each of the four age groups. Piglets of all ages vocalized intensely during isolation, but call rate was lower with older piglets, especially for high-frequency calls (>500 Hz). When returned to the sow, piglets made distinctive `quacking vocalizations, and older piglets produced fewer of these calls than younger piglets. Experiment 2 involved two treatments: weaning age and diet quality. Piglets were weaned at either 2 weeks of age and onto a diet formulated for piglets of this age, or at 4 weeks of age and fed either a diet typically provided for piglets of this age or a more palatable and nutritionally complex diet. Three piglets from each of 16 litters were assigned to each of the three treatment groups. We monitored vocalizations over the first 3 days after weaning, and measured the incidence of belly-nosing during the subsequent week. Piglets weaned onto the standard diet at 4 weeks produced high-frequency calls (>500 Hz) at a significantly higher rate than those weaned onto the more complex diet, but there was no effect of diet on the incidence of belly-nosing. Piglets weaned at 2 weeks produced more high-frequency calls and performed more belly-nosing than piglets weaned at 4 weeks onto either diet. Thus the behavioural response to separation is greater at younger ages both when the period of separation is too short for diet to be a factor (Experiment 1) and when younger piglets are provided with a specialized diet that allows them to achieve acceptable weight gain after weaning (Experiment 2). These results indicate that separation distress and frustration of suckling motivation are significant problems when piglets are weaned at less than 4 weeks of age.

Birth weight variation in the domestic pig: effects on offspring survival, weight gain and suckling behaviour

In domestic pigs, litter-mates often vary considerably in birth weight. To examine whether this size variation influences piglet survival, weight gain and suckling behaviour, we experimentally manipulated the number and size distribution of litter-mates in 51 litters. Litters were small (eight or nine piglets) or large (11 or 12 piglets) compared to the herd mean of 10 piglets, and were made more or less variable in weight by using the largest and smallest quartiles of two combined litters (variable) or the middle two quartiles (uniform). Weights were measured on days 0, 3 and 21. Behavioural measures (percent of nursings missed, mean teat consistency score, per capita number of teat disputes before milk ejection, and percent time spent in teat disputes in the 20min after milk ejection) were recorded on days 1, 4, 10 and 17. Piglet weight variation (percent of coefficient of variation, CV) almost doubled over the 21 days in uniform litters and actually decreased in variable litters, but still remained higher in the variable litters. Overall, survival, percent of nursings missed, consistency in piglets use of teats, number of teat disputes, percent time a piglet spent in teat disputes after milk ejection, and weight gain were unaffected by birth weight variation although there was a tendency (P=0.09) for more piglet deaths in variable litters. Behavioural measures of sibling competition were higher in large litters. The data provide little support for the hypotheses that high birth weight variation results in decreased survival, or that it permits rapid establishment of dominance, thereby reducing wasteful competitive behaviour in surviving piglets.

Armed sibling rivalry among suckling piglets

SummaryA piglets most precious possession Is the teat that he fattens his flesh on. He fights for his teat with tenacity Against any siblings audacity. The piglet, to arm for this mission, Is born with a warlike dentition Of eight tiny tusks, sharp as sabres, Which help in impressing the neighbors; But to render these weapons less harrowing, Most farmers remove them at farrowing. We studied pig sisters and brothers When some had their teeth, but not others. We found that when siblings arent many, The weapons help little if any, But when there are many per litter, The teeth help their owners grow fitter. But how did selection begin To make weapons to use against kin?

Attraction to blood as a factor in tail-biting by pigs

Abstract Canvas models, about the size of a pigs tail, were impregnated with pigs blood or left plain, and were presented to pigs for 12 days in a 2-choice preference test. The pigs showed large, consistent, individual differences in response: some pigs chewed the models continuously while others chewed only slightly; some chewed much more on the blood-covered model, while others showed no preference. On average, the pigs chewed considerably more on the blood-covered model than on the plain one. In a second experiment, pigs presented with a choice test involving a blood-covered and a plain model showed a significant increase in chewing over a baseline level seen with plain models only. It is suggested that this strong but highly variable response to blood could explain how a relatively minor tail injury can stimulate a large but unpredictable increase in tail-biting among pigs.

Parent–offspring resource allocation in domestic pigs

Behavioural research on domestic pigs has included parent–offspring conflict, sibling competition, and the use of signals which influence resource allocation. In this paper, we review key sow–piglet behavioural studies and discuss their relevance to resource allocation theory. Sibling competition begins in the uterus and continues after birth, as piglets compete directly for access to the sow’s teats. This competition is made more severe by a unique dentition, which newborn piglets use to lacerate the faces of siblings during teat disputes. Competition often leads to the death of some littermates, especially those of low birth weight. Piglets also compete indirectly for milk, apparently by stimulating milk production at the teats that they habitually use at the expense of milk production by other teats. The complex nursing behavior of the sow appears designed to prevent the more vigorous piglets from monopolizing the milk. Sows give vocal signals which both attract piglets to suckle and synchronize their behavior during nursing episodes. Piglets give loud vocal signals when separated from the sow; calls which vary in intensity and appear to be honest signals of need. Udder massage by piglets may also serve as an honest signal of need. Parent–offspring conflict has been demonstrated experimentally in pigs. Specifically, when given the opportunity to control contact with their piglets, sows nurse less frequently, provide less milk, and lose less weight during lactation than sows that cannot control their level of contact. Because of this interesting natural history and because they are so amenable to experimentation, domestic pigs provide a rich system for testing ideas drawn from resource allocation theory.

Alternative housing for sows and litters.

Abstract ‘Sow-controlled housing has been developed to address welfare and production concerns associated with close confinement of the lactating sow and her litter, by permitting the sow to leave the litter at will. However, there is a risk that variation in the use of the piglet-free (‘get-away) area may lead to inadequate maternal care in some cases or to failure to benefit from the system in others. To understand use of a get-away area more fully and to develop ways to predict or modify it, we analysed a large data set ( n =96litters) derived from three previous experiments and a new study on sow-controlled housing. Sows use of the get-away area was highly variable, and the variation increased with piglet age from 1 to 4 weeks. Relative use of the get-away area was consistent among individual sows over the course of lactation and negatively related to nursing frequency. Sows tested in two or more lactations showed no consistency from one lactation to another. Sows that used the get-away area more, especially late in lactation, tended to be lighter at parturition and to have larger litters at birth and at weaning. Sow weight loss and average piglet weight gain tended to decrease as use of the get-away area increased and nursing frequency decreased. Five tests of maternal responsiveness to stimuli associated with piglet distress revealed consistent individual differences and a positive association between sensitivity to an isolated piglet and the amount of get-away use. We conclude that use of the get-away area is an expression in part of the sows investment in her offspring, and that it is not necessarily indicative of low parental motivation.