The effect of parity and environmental restriction on behavioural and physiological responses of pre-parturient pigs

There is increasing evidence that restriction of pre-parturient behaviour i n pigs is stress-inducing, characterised by an elevation in hypothalamic-pi tuitary-adrenal (HPA) activity in gilts. To determine whether pigs adapt to behavioural restriction, through modification of nest-building behaviour, we studied pre-parturient pigs in either farrowing crates (no bedding, n = 7) or straw-bedded pens (n = 7) in their first (gilts) and second (sows) pa rity. with physiological measurements being taken in the second parity. Obs ervations and blood sampling were carried out during the preparturient phas e. Crated pigs changed posture more often than penned pigs (F-1,F-12 = 7.06 , P < 0.05), with the number of posture changes reducing across parities in both environments. The reduction in posture changing was more apparent in the crated sows which may indicate that attempted nest-building behaviour o f sows with prior experience of farrowing crates is less fragmented. The cr ated pigs spent a greater proportion of time sitting across both parities ( F-1,F-12 = 9.4, P < 0.01), and spent less time manipulating available subst rates (F-1,F-12 = 10.67, P < 0.05). There was a tendency for penned pigs to spend a greater proportion of time standing (F-1,F-12 = 3.77, P = 0.076) w ith peak nesting behaviour occurring earlier in relation to parturition tha n in crated pigs. In addition penned sows performed more floor-directed beh aviour than penned gilts, and at an earlier stage in relation to parturitio n. However, crated sows also performed peak nest-building earlier than crat ed gilts. Plasma cortisol profiles indicated elevated HPA activity in crate d sows during the pre-parturient period (F-42,F-303 = 1.43, P < 0.05) sugge sting increased physiological stress, however, the difference between crate d and penned sows was less than that previously seen in gilts. The increase d range of pre-parturient behaviours seen in the penned sows suggests that experience may result in an 'improvement' in their nest-building behaviour: earlier preparation of the nest site and then subsequent manipulation of s ubstrates. The crated sows appeared to show some behavioural adaptation to the crate environment; earlier peak in floor directed behaviour and total s ubstrate directed behaviour, reduced posture changing. In conclusion the ne st-building behaviour of pigs is modified over parities with adaptation to the behavioural restrictions imposed by the farrowing crate. However, this adaptation, through prior experience, does not completely reduce the elevat ion in HPA activity previously reported in pre-parturient crated gilts. (C) 2001 Elsevier Science B.V. All rights reserved.