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. Th e behaviour of 16 Large White X Landrace female pigs was recorded around fa rrowing which involved recording the pig's posture and her response when pi glets 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 o f 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 almos t all of the time in lateral recumbency. The results also show that farrowi ng sows are generally unresponsive to their piglets during farrowing. Sows receiving naloxone became more responsive towards their piglets. The change s 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, ch aracterised by lateral lying and unresponsiveness to piglets, may be advant ageous by maximising suckling opportunities and reducing the risk of crushi ng piglets and of attracting predators to the nest. (C) 1999 Elsevier Scien ce B.V. All rights reserved.