Investigating management strategies of large litters in pigs
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Modern hyper-prolific sows often do not have enough teats to feed all of their piglets. The resulting competition for colostrum and milk hampers piglet growth and survival. This is exacerbated by low birth-weights, which are also common in large litters. Three experiments were conducted for this thesis; each investigated a management strategy hypothesised to improve outcomes for piglets from large litters. The first experiment evaluated the use of nurse sows to rear supernumerous piglets (i.e. when there are more piglets than teats). At 1 day old, piglets from large litters either remained with their mother or were moved to a nurse sow who was either 7 or 21 days into lactation. Aspects of piglet (growth, survival and suckling behaviour) and sow (salivary cortisol, back-fat thickness, body lesions, and nursing behaviour) welfare were monitored until weaning. Rearing by a nurse sow did not compromise pre-weaning survival, compared to rearing by the mother, regardless of the nurse sows’ stage of lactation (7 or 21 days) when the piglets were transferred to her. Piglets reared by a nurse sow were initially heavier than piglets remaining with their dam, but all piglets were weaned at similar weights. Regardless of whether a nurse sow or biological mother, sows in late lactation had shorter nursing bouts and their litter showed more fighting behaviour, compared to sows in early lactation. Despite longer lactation length, nurse sows did not differ from biological mothers in salivary cortisol concentration, backfat thickness and body lesion scores. The second experiment looked at using an artificial rearing system to rear 7 day old piglets until weaning. Litters of 12 piglets were assigned at 7 days old to be either sow-reared (SR) or artificially-reared (AR) until weaning. Pre-weaning survival, growth and behaviour were recorded, emotional state was assessed using Qualitative Behavioural Assessment pre- and post-weaning, and reactivity tests were conducted post-weaning. Survival did not differ between treatments. AR piglets were lighter than SR piglets from the day following transfer until weaning. They performed more negative behaviours (belly-nosing, ear and tail biting) and their emotional state was scored lower pre-weaning, compared to SR piglets. However, post-weaning the emotional state of AR piglets was scored higher than SR pigs and AR piglets had a lower emotional reaction to a fear test (startling event) and human contact. The third experiment evaluated whether 2ml of an energy-rich neonatal supplement (coconut oil or a commercial product) would enhance survival and vitality of low birth-weight piglets. At three hours post-birth, low birthweight piglets (<1.1 kg) were dosed with one of the supplements, water, or sham-dosed. Blood glucose content, rectal temperature, and pre-weaning survival and growth were recorded but none were affected by treatment. Post-weaning, piglets were tested for spatial learning and memory in a T-maze set-up, or were tested for short-term memory in a spontaneous object recognition test. There were no treatment differences on the performance of pigs in any of the two tests, meaning that the birth energy supplementation did not enhance post-weaning cognitive performances. This thesis demonstrated that a single dose of energy supplementation at birth did not improve outcomes for low birth-weight piglets, and that the rearing strategies to promote piglet survival in large litters do work in terms of survival but can impair some aspects of piglet welfare and development. The most pronounced welfare impacts were observed with artificial rearing. Therefore management of large litters remains a significant challenge and the strategies investigated deserve further improvements.