Emma M. Baxter

Investigating the behavioural and physiological indicators of neonatal survival in pigs

Survival is reduced in low birth weight piglets, which display poor thermoregulatory abilities and are slow to acquire colostrum. Our aim was to identify additional behavioural and physiological indicators of piglet survival incorporating traits reflective of both the intrauterine and extrauterine environment. Data were collected from 135 piglets from 10 Large White x Landrace sows to investigate which physiological measurements (e.g. individual placental traits), and which behavioural measurements (e.g. the quantification of piglet vigour), were the best indicators of piglet survival. Generalised linear models confirmed piglet birth weight as a critical survival factor. However, with respect to stillborn mortality, piglet shape and size, as measured by ponderal index (birth weight/(crown-rump length)(3)), body mass index (birth weight/(crown-rump length)(2)), respectively, and farrowing birth order were better indicators. With respect to live-born mortality, postnatal survival factors identified as crucial were birth weight, vigour independent of birth weight, and the latency to first suckle. These results highlight the importance of the intrauterine environment for postnatal physiological and behavioural adaptation and identify additional factors influencing piglet neonatal survival.

The welfare implications of large litter size in the domestic pig I: biological factors

Increasing litter size has long been a goal of pig breeders and producers, and may have implications for pig (Sus scrofa domesticus) welfare. This paper reviews the scientific evidence on biological factors affecting sow and piglet welfare in relation to large litter size. It is concluded that, in a number of ways, large litter size is a risk factor for decreased animal welfare in pig production. Increased litter size is associated with increased piglet mortality, which is likely to be associated with significant negative animal welfare impacts. In surviving piglets, many of the causes of mortality can also occur in non-lethal forms that cause suffering. Intense teat competition may increase the likelihood that some piglets do not gain adequate access to milk, causing starvation in the short term and possibly long-term detriments to health. Also, increased litter size leads to more piglets with low birth weight which is associated with a variety of negative long-term effects. Finally, increased production pressure placed on sows bearing large litters may produce health and welfare concerns for the sow. However, possible biological approaches to mitigating health and welfare issues associated with large litters are being implemented. An important mitigation strategy is genetic selection encompassing traits that promote piglet survival, vitality and growth. Sow nutrition and the minimisation of stress during gestation could also contribute to improving outcomes in terms of piglet welfare. Awareness of the possible negative welfare consequences of large litter size in pigs should lead to further active measures being taken to mitigate the mentioned effects.

The welfare implications of large litter size in the domestic pig II: Management factors

Increasing litter size has long been a goal of pig (Sus scrofa domesticus) breeders and producers in many countries. Whilst this has economic and environmental benefits for the pig industry, there are also implications for pig welfare. Certain management interventions are used when litter size routinely exceeds the ability of individual sows to successfully rear all the piglets (ie viable piglets outnumber functional teats). Such interventions include: tooth reduction; split suckling; cross-fostering; use of nurse sow systems and early weaning, including split weaning; and use of artificial rearing systems. These practices raise welfare questions for both the piglets and sow and are described and discussed in this review. In addition, possible management approaches which might mitigate health and welfare issues associated with large litters are identified. These include early intervention to provide increased care for vulnerable neonates and improvements to farrowing accommodation to mitigate negative effects, particularly for nurse sows. An important concept is that management at all stages of the reproductive cycle, not simply in the farrowing accommodation, can impact on piglet outcomes. For example, poor stockhandling at earlier stages of the reproductive cycle can create fearful animals with increased likelihood of showing poor maternal behaviour. Benefits of good sow and litter management, including positive human-animal relationships, are discussed. Such practices apply to all production situations, not just those involving large litters. However, given that interventions for large litters involve increased handling of piglets and increased interaction with sows, there are likely to be even greater benefits for management of hyper-prolific herds.

Alternative farrowing systems: design criteria for farrowing systems based on the biological needs of sows and piglets

The construction of a suitable farrowing environment is a continuing dilemma: the piglets needs must be matched with those of the sow and the farmer during the main phases that constitute farrowing: nest building, parturition and lactation. Difficulties exist in resolving the various conflicts of interest between and within these three parties (e.g. sow v. farmer: space needed for nest building v. space needed to maximise the amount of farrowing accommodation, or sow v. sow: ensuring the survival of the current litter v. maintaining condition for future litters). Thus, the challenge is to resolve these conflicts and design a system that maximises sow and piglet welfare while maintaining an economically efficient and sustainable enterprise. In order to successfully design a farrowing and lactation environment, it is necessary to consider the biological needs of both the sow and her litter. The natural behaviour of the sow has been well documented and very little variation exists between reports of peri-parturient behaviour observed in extensively kept domestic sows and their wild counterparts. The failure for domestication to significantly alter these behavioural patterns provides evidence that they are biologically significant and that the commercial farrowing environment should attempt to accommodate this behavioural repertoire. In addition, the behavioural needs of the piglets, as well as the physiological needs of both sows and their offspring should be considered. This article aims to review the considerable body of literature detailing the behavioural repertoire of sows and their offspring during the different phases of farrowing, and the accompanying physiological processes. The focus is on identifying biological needs of the animals involved in order to synthesise the appropriate design criteria for farrowing and lactation systems, which should optimise both welfare and animal production.

Genetic parameters of piglet survival and birth weight from a two-generation crossbreeding experiment under outdoor conditions designed to disentangle direct and maternal effects.

Multivariate Bayesian linear-threshold models were used to estimate genetic parameters of peri- and postnatal piglet survival and individual birth weight of piglets reared under outdoor conditions. Data of 21,835 individual piglet observations were available from a 2-generation crossbreeding experiment selected for direct and maternal genetic effects of postnatal piglet survival on piglet and dam levels, respectively. In the first generation, approximately one-half of the Landrace sires used were selected for large or average breeding values of maternal genetic effects on postnatal piglet survival, whereas in the second generation the Large White sires used were selected for direct genetic effects of the same trait. Estimates of direct and maternal heritability were 0.21 and 0.15, 0.24 and 0.14, and 0.36 and 0.28 for piglet survival at birth and during the nursing period, and individual birth weight, respectively. In particular, direct heritabilities are substantially larger than those from the literature estimated for indoor-reared piglets, suggesting that genetic effects of these traits are substantially greater under outdoor conditions. Direct or maternal genetic correlations between survival traits or with birth weight were small (ranging from 0.06 to 0.17), indicating that peri- and postnatal survival are genetically under rather different control, and survival was only slightly positively influenced by birth weight. There were significant (P < 0.05) negative genetic correlations between direct and maternal genetic effects within each of the analyzed traits ranging from -0.36 to -0.45, which have to be considered when selecting for piglet survival. Adjustment of traits for litter size or inclusion of genetic groups showed insignificant effects on the magnitude of the estimated genetic parameters. The magnitude of genetic parameters suggested that there is substantial potential for genetic improvement of survival traits and birth weight in direct and maternal genetic effects, especially when piglets are kept under outdoor conditions.

The Weaker Sex? The Propensity for Male-Biased Piglet Mortality

For the most part solutions to farm animal welfare issues, such as piglet mortality, are likely to lie within the scientific disciplines of environmental design and genetic selection, however understanding the ecological basis of some of the complex dynamics observed between parent and offspring could make a valuable contribution. One interesting, and often discussed, aspect of mortality is the propensity for it to be sex-biased. This study investigated whether known physiological and behavioural indicators of piglet survival differed between the sexes and whether life history strategies (often reported in wild or feral populations) relating to parental investment were being displayed in a domestic population of pigs. Sex ratio (proportion of males (males/males+females)) at birth was 0.54 and sex allocation (maternal investment measured as piglet birth weight/litter weight) was statistically significantly male-biased at 0.55 (t35 = 2.51 P = 0.017), suggesting that sows invested more in sons than daughters during gestation. Despite this investment in birth weight, a known survival indicator, total pre-weaning male mortality was statistically significantly higher than female mortality (12% vs. 7% respectively z = 2.06 P = 0.040). Males tended to suffer from crushing by the sow more than females and statistically significantly more males died from disease-related causes. Although males were born on average heavier, with higher body mass index and ponderal index, these differences were not sustained. In addition male piglets showed impaired thermoregulation compared to females. These results suggest male-biased mortality exists despite greater initial maternal investment, and therefore reflects the greater susceptibility of this sex to causal mortality factors. Life history strategies are being displayed by a domestic population of pigs with sows in this study displaying a form of parental optimism by allocating greater resources at birth to males and providing an over-supply of this more vulnerable sex in expectation of sex-biased mortality.

Economic evaluation of high welfare indoor farrowing systems for pigs

New livestock housing systems designed to improve animal welfare will only see large-scale commercial adoption if they improve profitability, or are at least cost neutral to the farm business. Economic evaluation of new system developments is therefore essential to determine their effect on cost of production and hence the extent of any market premium necessary to stimulate adoption. This paper describes such an evaluation in relation to high welfare farrowing systems for sows where any potential system needs to reconcile the behavioural needs of the sow with piglet survivability, acceptable capital and running costs, farm practicality and ease of management. In the Defra-sponsored PigSAFE project, a new farrowing system has been developed which comprises a loose, straw-bedded pen with embedded design features which promote piglet survival. Data on this and four other farrowing systems (new systems: 360° Farrower and a Danish pen; existing systems: crate and outdoor paddock) were used to populate a model of production cost taking account of both capital and running costs (feed, labour, bedding etc). Assuming equitable pig performance across all indoor farrowing systems, the model estimated a higher production cost for non-crate systems by 1.6, 1.7 and 3.5%, respectively, for 360° Farrower, Danish and PigSAFE systems on a per-sow basis. The outdoor production system had the lowest production cost. An online survey of pig producers confirmed that, whilst some producers would consider installing a non-crate system, the majority of producers remain cautious about considering alternatives to the farrowing crate. If pig performance in alternative indoor systems could be improved from the crate baseline (eg through reduced piglet mortality, improved weaning weight or sow re-breeding), then the differential cost of production could be reduced. Indeed, with further innovation by pig producers, management of alternative farrowing systems may evolve to a point where there can be improvements in both welfare and pig production. However, larger data sets of alternative systems on commercial farms will be needed to explore fully the welfare/production interface before such a relationship can be confirmed for those pig producers who will be replacing their units in the next ten years.

Piglet mortality and morbidity: Inevitable or unacceptable?

Abstract Piglet mortality is a problem with complex aetiology, predisposed by the natural biology of a polytocous species which produces multiple offspring allocated disproportionate resources both in the pre- and post-natal environment. Intensive sibling rivalry to acquire limited uterine resources pre-natally, and then limited nutrients post-natally, leads to a high risk of mortality for the weakest among the offspring. In the domestic pig these risks have been exacerbated by intensive selection for economic traits such as prolificacy and leanness. Thus it would seem a certain amount of mortality is to be expected. The acceptability of death can be a subject of much ethical debate. However, even if death itself is not considered a welfare issue, the manner of dying is, particularly when it involves pain and/or suffering. Thus, whilst the life history strategy of the pig encompasses mortality risk, at what point does the inevitable become unacceptable for animal welfare?

Sow welfare in the farrowing crate and alternatives

The farrowing crate poses a welfare dilemma; the restriction of sow movement interferes with the performance of species-specific behaviours such as nest-building, orientation, exploration and communication with the piglets and leads to increased physiological stress. However, allowing the sow more freedom to perform motivated behaviours often results in increased crushing of piglets and hence a piglet welfare problem. Although alternative farrowing systems exist, a major barrier to the uptake of these systems is that they must deliver acceptable levels of piglet mortality. Research efforts have led to successful development of loose farrowing systems delivering high performance and high welfare. The key to success has been recognising that allowing the display of species-typical behaviours contributes to the biological fitness of the animal, which encompasses important economic performance parameters including number of offspring produced, viability of offspring and maternal rearing ability. Further welfare challenges have developed as sows have been subject to genetic selection pressure for leanness and prolificacy. A more balanced equation where the cost of maternal investment (for instance shoulder lesions, loss of body condition, lower residual reproductive output and thus shorter longevity) is balanced against the increase in the number of piglets born and weaned, is needed as a basis for breeding programs. Therefore system design optimisation must be accompanied by optimisation of both human inputs (i.e., through augmentation of management) and animal inputs (i.e., through appropriate genetic selection strategies).

Mitigating hunger in pregnant sows

Abstract Pregnant (dry) sows are fed a restricted food ration to ensure good health, production and longevity, but this results in behavioural signs of hunger: oral behaviours increase and may be redirected ‘unnaturally’ towards non-food, prompting welfare concerns. ‘Dietary fibre’ encompasses a variety of chemical classes, with a variety of physiochemical properties. It reduces abnormal oral behaviours, and fibres that are soluble and fermentable in the hindgut appear to prolong satiety, reduce activity and improve welfare. EU rules require fibre in dry sow diets and access to foraging materials but implementation differs across member states. Diet, feeding system, number of meals and social structure combine to affect welfare of the sow and developing piglets, e.g., through pre-natal stress. Current breeding trends to increasing litter size and associated practices like the use of ‘nurse sows’ may require a rethink of sow nutrition to safeguard longevity and welfare.