The responsiveness of sows to their piglets in relation to the length of parturition and the involvement of endogenous opioids

The aim of this study was to describe maternal behaviour in the pig and to investigate the effect of endogenous opioids on maternal responsiveness. The behaviour of 16 Large White X Landrace female pigs was recorded around farrowing which involved recording the pig's posture and her response when piglets were present at her nose. To determine the role of endogenous opioids, sows were injected (i.m.) with either naloxone, an opioid antagonist, (1 mg kg(-1) bodyweight (n = 8)) or saline (n = 8) at 3.75 h after the birth of the first piglet. Generally the initial period following the birth of the first piglet seemed to be the most active after which the sows spent almost all of the time in lateral recumbency. The results also show that farrowing sows are generally unresponsive to their piglets during farrowing. Sows receiving naloxone became more responsive towards their piglets. The changes seen in posture and responsiveness to piglets were delayed in sows with a longer parturition suggesting some involvement of cumulative piglet births on passivity. It is proposed that opioid-mediated passivity in the pig, characterised by lateral lying and unresponsiveness to piglets, may be advantageous by maximising suckling opportunities and reducing the risk of crushing piglets and of attracting predators to the nest. (C) 1999 Elsevier Science B.V. All rights reserved.