The effect of environment on behavioural activity, ACTH, β-endorphin and cortisol in pre-farrowing gilts

This study examined the temporal relationships between behavioural activity and hormones associated with stress in gilts farrowing in two environments. Thirty-one Large White x Landrace gilts with indwelling jugular catheters were blood sampled daily (08.00 and 16.00 h) from 10 days before their expected parturition date (EPD). Five days before EPD they were moved to either a farrowing crate (C) with no bedding, or a pen (P) (2.5 m x 3.0 m) with straw provided and were blood sampled daily at 08.00, 12.00 and 16.00 h. Around 12 h before the onset of farrowing an extension was fitted to the catheter and blood samples were taken remotely at 30-min intervals. The posture of the gilts was recorded using 5-min scan samples over the 24 h pre-farrowing. The proportion of scans standing (nn index of activity) teas strongly affected by time (P < 0.001) with peak levels at approximately 8 h pre-farrowing in both treatments, and by treatment (0.25 v. 0.33 (s.e.d. 0.03) for C and P gilts respectively; P < 0.05). Plasma cortisol concentrations also increased before farrowing (P < 0.001) reaching a peak at 12 to 6 h pre-farrowing. Crated gilts had higher cortisol concentrations than penned gilts (overall mean 41.5 v. 30.7 (s.e.d. 3.8) mu g/l for C and P gilts respectively; P < 0.05) at 24 to 12 (P < 0.05), 12 to 6 (P < 0.01) and 6 to 2 (P < 0.05) h pre-farrowing. Plasma ACTH concentration showed a similar pattern to cortisol over the pre-parturient period, peaking at 12 h pre-farrowing in both treatments (time: P < 0.001); crated gilts had significantly higher concentrations of ACTH at 6 h pre-farrowing only (P < 0.05). Plasma beta-endorphin concentrations also showed a gradual rise (P < 0.001) towards parturition; however no treatment differences were seen. These results suggest that the pituitary-adrenal (PA) axis is stimulated during pre-farrowing activity irrespective of farrowing environment. Crates, without bedding, further stimulate the PA axis over the pre-farrowing period perhaps by preventing nest building. The rise in beta-endorphin may be involved in an endogenous defence against parturition pain.