S. A. Edwards

Perinatal mortality in the pig: environmental or physiological solutions?

Abstract The evolutionary strategy adopted by the pig is to produce a large number of relatively undeveloped offspring. Such a strategy demands that relatively little investment is made in each individual piglet pre-natally, and that piglets which are surplus to resources should die at an early stage with least prejudice to their littermates. Thus, inherent variation in neonatal competitiveness is an advantage and survival of the strongest is promoted. Genetic selection strategies resulting in increased litter size and reduced physiological maturity at birth have compounded these effects, making piglet mortality an intractable problem. Records of piglet mortality in commercial units indicate that most deaths of liveborn piglets are attributed to crushing and starvation, but these ultimate causes are often secondary to the effects of perinatal hypothermia. Piglet survival is the outcome of complex interactions between the sow, the piglet and the environment. Commercial strategy has focused on improving the farrowing environment to modify sow behaviour and increase human intervention. However, concerns about the welfare implications of confining sows in farrowing crates may limit the use of such approaches in the future and change the focus towards genetic selection for characteristics in both the dam and offspring which promote survival. Methods of improving the inherent viability of the piglet, for example by increasing birth weight, neonatal vigour and thermoregulatory ability, have been commercially less effective to date, with intra-partum hypoxia exerting an overwhelming influence. A better understanding of neonatal and maternal physiology in relation to placental transfer of nutrients, regulation of the parturition process, colostrum transfer and expression of appropriate maternal behaviour is required for the development of effective future solutions.

A systematic approach towards developing environmental enrichment for pigs

Abstract Environmental enrichment is often implemented without considering the requirements of the animals within their environment and without specifying desired functional behaviours. An approach towards the development of species-specific environmental enrichment for pigs is presented here, which attempts to avoid introducing enrichment on an intuitive basis and instead uses behavioural observations of interactions with enrichment to analyse which characteristics of objects stimulate exploratory behaviour in pigs. The intensity of interactions of 222 groups of three weaner and 222 groups of three grower pigs with 74 different objects were studied during 5 days in order to find the characteristics that the favoured objects had in common. Each object was described using 28 descriptors and these were correlated with object-directed behaviour scores obtained from videos. Multiple Stepwise Regression analysis identified which of the characteristics played a major role in determining the level of object-directed behaviour. The main characteristics emerging on day 1 (odorous, deformable, not rootable, not attached, chewable) reflected the initial attractiveness of an object. The main characteristics emerging on day 5 (ingestible, destructible, contained, not particulate, not rootable) reflected sustained attention towards an object. These results underline the importance of enrichment for pigs which stimulates foraging and explorative behaviour. The approach proved to be a useful tool and may be used for other species to assess the importance of different environmental features. The optimal combination of the important characteristics can be used to design functional environmental enrichment, which takes into consideration species-relevant requirements.

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.

Effect of dietary fibre on the behaviour and health of the restricted fed sow

Abstract The usual restricted feeding level during gestation, whilst adequate to maximise economic performance, might not fulfil behavioural needs of the sow. Hunger and frustration of feeding motivation have been linked to the occurrence of stereotypic activity, and accentuate aggression and feeding competition in group-housing systems. Incorporation of fibre in diets to increase bulk, without changing the daily dietary energy supply, has been shown to result in at least a doubling of eating time, a 20% reduction in feeding rate, a 30% reduction in operant response in feed motivation tests, a reduction of 7–50% in stereotypic behaviour, and a decrease in general restlessness and aggression. Results suggest a reduced feeding motivation, but only if nutrient intake with fibrous diets meets the nutrient requirements of the animals. Investigations of circulating glucose, insulin and volatile fatty acid levels in sows fed fibrous diets indicate a more constant nutrient absorption and greater microbial fermentation in the gut, which should increase satiety. There is inadequate information on effects of dietary fibre on physiological stress and health. In addition to welfare considerations, a range of technical requirements and economic factors must be considered when making decisions on the use of dietary fibre during gestation.

The effect of space allowance on performance, aggression and immune competence of growing pigs housed on straw deep-litter at different group sizes.

Legislation controlling minimum floor space allowances for pigs rarely allows flexibility for variations in the physical and social environment. The space requirement of pigs housed in large groups and on deep-straw bedding has not been adequately addressed. Pigs, housed on deep-straw for 6 weeks in groups of 20 or 80, were provided with a low (50 kg/m2) or high (32 kg/m2) space allowance in an experiment of 2×2 factorial design replicated four times. Low space allowance, irrespective of group size, did not influence average daily gain (ADG), but tended to improve efficiency of growth (P<0.1). Groups of 80 pigs had a lower ADG than groups of 20 (0.684 vs. 0.732 S.E.D. 0.0142 kg/day, P<0.01). Within pen variation in ADG was similar for each treatment. Number of skin lesions were elevated by low space allowance (10.1 vs. 8.5 s.e.d. 0.68 lesions per pig for low and high space allowance respectively, P<0.05). The humoral response to an antigen challenge (Newcastle disease virus) was lower when provided with small space allowance (P<0.01). Since the main effects did not interact, the poorer ADG of large groups, and the higher lesion score and suppressed immune response of pigs provided with lower space allowance, suggest that these conditions may independently compromise productivity and welfare.

Social rank and feeding behaviour of group-housed sows fed competitively or ad libitum

Certain feeding systems commonly used in practice can result in competition for food and be disadvantageous for low-ranking sows. Feeding a low density diet ad libitum should abolish competition for food and give all sows equal opportunity to obtain food. In this experiment, the consequences of the availability of food on live weight gain and feeding behaviour of sows of different social rank were investigated. Four groups of 12 multiparous sows housed in straw bedded pens were allocated to one of two feeding regimens and remained on treatment throughout gestation. Two groups were floor-fed 3.0 kg per sow of a conventional diet (13.1 MJ (DE) kg−1) once daily, the other two groups received a high-fibre diet (11.2 MJ (DE) kg−1) ad libitum. Dominance ranks were determined in a paired food competition test and from observations of social interactions in the group situation. The paired competition test indicated that the hierarchies in the four pens were almost linear. The hierarchies thus determined were a good representation of feed-related dominance hierarchies in the group situation. When sufficient social interactions were recorded in the group situation, the dominance rank determined from these was similar to the paired competition test. In the ad libitum pens insufficient interactions could be observed in a short time-span. These sows spent, on average, 1.5 h day−1 feeding. They preferred to feed singly, but low-ranking sows had to feed more often at less preferred feeding places and together with other sows. Low-ranking sows gained less weight than high-ranking sows in the floor-fed pens, but not in the ad libitum pens. By changing their feeding strategy, low-ranking sows in an ad libitum feeding system could achieve comparable intake with higher-ranking animals.

Effect of dietary fibre and feeding system on activity and oral behaviour of group housed gilts

Abstract The low feeding level common in practice for dry sows has been linked to the occurrence of stereotypies. In this experiment the effects of a high fibre diet offered at a restricted level or ad libitum during gestation, on activity and oral behaviour of group housed gilts were studied. A total of 54 gilts were allocated to three treatments and housed in groups of six in straw bedded pens with individual feeding stalls. The treatments consisted of: control (C) 2.0 kg of a conventional diet (13.0 MJ DE, 44 g crude fibre per kg diet) fed once daily; restricted fibre (RF) 2.3 kg of a diet containing 500 g unmolassed sugar-beet pulp per kg (11.3 MJ DE, 107 g crude fibre per kg diet) fed once daily; ad libitum (AF), the same fibrous diet offered ad libitum from a single space hopper. Direct observations at feeding time showed that RF gilts took longer to consume their ration than C gilts and that fibre fed gilts were less active in the post-feeding period. This was confirmed by time-lapse video-recordings, which showed that fibre fed gilts spent more time lying during a 24-h period. AF gilts spent, on average, 100 min day −1 feeding. Feeding the fibrous diet once daily reduced the incidence of oral behaviours relative to treatment C, and the oral behaviours which still occurred did not have the appearance of stereotypies. Very few abnormal oral behaviours were observed when the fibrous diet was offered ad libitum. The time spent rooting was reduced when the diet was offered once daily, but was reduced even further when the diet was offered ad libitum. This suggests that the feeding motivation of gilts which received a fibrous diet was less than that of the control gilts.

Provision of straw as a foraging substrate reduces the development of excessive chain and bar manipulation in food restricted sows

Pregnant sows fed at commercial levels remain highly food motivated for most of the day. The inability to express this behaviour appropriately may, under certain conditions, result in the development of abnormal oral activities such as stereotypic chain and bar manipulation. Ninety-six gilts, all between 1 and 3 weeks post service, were entered into a 2X2 factorial design comparing food level (low, 1.8 kg/23 MJ day(-1) (L); high, 3.2 kg/40 MJ day(-1) (H)) and the provision of a foraging substrate (S, straw; N, no straw). The gilts were loose housed in groups of six with individual stalls. A 70 cm chain loop was attached to the front of each stair. The sows were fed at 09:00 h, during which time S sows received straw (approximately 1.5 kg per sow). Behaviour was recorded over the first two parities, by time sampling for the 2 and 6 h after the start of feeding and over 24 h using video recordings. Activity levels were highest just after feeding, with L sows being more active than H sows (L vs. H, 79% vs. 49% for the second hour after the start of feeding, F-1,F-12 = 41.5, P <0.001). Most of the postprandial activity consisted of manipulating substrates. In LN sows, particularly in Parity 2, this behaviour was mainly directed towards chains and bars, resulting in levels three to four times higher than in other groups (26%, 7%, 4% and 4% for the second hour after feeding for LN, LS, HN and HS respectively; Tukeys HSD, P <0.05). LS sows directed their foraging behaviour mainly towards the straw. It is concluded that in food-restricted pregnant sows, abnormally high levels of chain and bar manipulation can be prevented by providing straw which apparently acts as a foraging substrate.

Behaviour, social interactions and lesion scores of group-housed sows in relation to floor space allowance

Abstract The space allowance appropriate for sows in group housing remains scientifically undefined, since the social space requirement of a group of animals and the factors which affect this are unknown. Eight established groups of six pregnant, multiparous sows were used in a replicated Latin Square design of experiment, with 7 day periods, to compare four pen sizes providing 2.0, 2.4, 3.6 or 4.8 m 2 /sow. For the last 48 h of each 7 day period, a continuous video recording was made to determine general behaviour and all social interactions. Time spent rooting increased progressively with increasing space allowance, whereas time spent sitting and standing inactive were both progressively reduced. The total frequency of social interactions and aggressive behaviour both increased with decreasing space allowance. The Attack:Retreat ratio was significantly higher, and the Avoidance Index significantly lower, in the smallest pen. All body regions had the highest count of lesions after sows had been in the smallest pen, with damage levels being reduced as pen area increased. Analysis of body lesion scores, combining incidence and severity, gave the same treatment effects. In conclusion, the results indicated that a minimum space of between 2.4 and 3.6 m 2 /sow was necessary in the conditions of this experiment to promote good welfare. This result cannot be generalised to situations of different group size, group stability or feeding method.

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.