THE EFFECT OF ENVIRONMENT ON BEHAVIORAL ACTIVITY, ACTH, BETA-ENDORPHIN AND CORTISOL IN PRE-FARROWING GILTS

This study examined the temporal relationships between behavioural act ivity and hormones associated with stress in gilts farrowing in two en vironments. Thirty-one Large White x Landrace gilts with indwelling ju gular catheters were blood sampled daily (08.00 and 16.00 h) from 10 d ays 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 da ily at 08.00, 12.00 and 16.00 h. Around 12 h before the onset of farro wing an extension was fitted to the catheter and blood samples were ta ken remotely at 30-min intervals. The posture of the gilts was recorde d using 5-min scan samples over the 24 h pre-farrowing. The proportion of scans standing (nn index of activity) teas strongly affected by ti me (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 an d P gilts respectively; P < 0.05). Plasma cortisol concentrations also increased before farrowing (P < 0.001) reaching a peak at 12 to 6 h p re-farrowing. Crated gilts had higher cortisol concentrations than pen ned gilts (overall mean 41.5 v. 30.7 (s.e.d. 3.8) mu g/l for C and P g ilts 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 sho wed a similar pattern to cortisol over the pre-parturient period, peak ing at 12 h pre-farrowing in both treatments (time: P < 0.001); crated gilts had significantly higher concentrations of ACTH at 6 h pre-farr owing only (P < 0.05). Plasma beta-endorphin concentrations also showe d a gradual rise (P < 0.001) towards parturition; however no treatment differences were seen. These results suggest that the pituitary-adren al (PA) axis is stimulated during pre-farrowing activity irrespective of farrowing environment. Crates, without bedding, further stimulate t he PA axis over the pre-farrowing period perhaps by preventing nest bu ilding. The rise in beta-endorphin may be involved in an endogenous de fence against parturition pain.