RESTRICTING MATERNAL SPACE DURING PARTURITION IN THE PIG - EFFECTS ONOXYTOCIN, VASOPRESSIN AND CORTISOL SECRETION FOLLOWING VAGINO-CERVICAL STIMULATION AND ADMINISTRATION OF NALOXONE

This experiment studied the effects on endocrine and birth parameters of parturient pigs produced by restricting maternal freedom of movemen t without otherwise altering environment. Six primiparous pigs (gilts) were each given a jugular catheter under anaesthesia 7 days before pa rturition and commenced birth in a strawed pen, 2.0 m X 1.5 m in size. Continuous automated blood sampling (3 ml min(-1)) from unrestrained gilts began following the blah of the first piglet (stage 1) and conti nued for 2 h. After at least 30 min of blood collection, maternal spac e was reduced to 2.0 m X 0.55 m by placing rails across the pen (stage 2). The scope for movement in stage 2 was similar to that offered by a farrowing crate. After at least 25 min each gilt was given the opioi d antagonist naloxone (1 mg kg(-1) i.v.: stage 3). At each stage, vagi no-cervical stimulation (VCS) was applied to mimic foetal ejection. No n-cervically stimulated oxytocin (OT) secretion between stages 1 and 2 was unchanged (P > 0.05) but increased significantly relative to both stages 1 and 2 following naloxone treatment for 15-20 min (P < 0.05, paired t-tests on log,, data). Following VCS in all stages plasma OT r ose (P < 0.05) for 1-2 min in a similar way to that seen previously fo llowing foetal ejection, the increases being proportionally similar ir respective of stage or baseline secretion. Cortisol secretion did not increase as a consequence of space restriction (mean +/- SEM concentra tions were 28.6 +/- 8.51 pmol l(-1) and 32.3 +/- 11.8 pmol l(-1) in st ages 1 and 2, respectively). In addition, VCS did not significantly af fect cortisol output. Lysine vasopressin concentrations were not affec ted as a consequence of either stage or VCS. Parturition was not inter rupted following space restriction of gilts. These data suggest that r educing maternal space allowance during parturition is not stressful w hen the process does not involve the movement of animals to novel surr oundings. (C) 1997 Elsevier Science B.V.