The effect of naloxone on reproductive behavior and plasma prolactin levels after weaning in third lactation sows
Resumen
The present study was undertaken to study the effect of small doses of naloxone on behavior, prolactin plasma levels, interval of weaning to first estrus, and duration of estrus in third lactation sows. Thirty York x Landrace sows weaned at 25 to 27 days postpartum were selected and separated at random in two groups of 15. One group served as control and the other received every twelve hours two mg of naloxone im. Treatment with small doses of naloxone started three days before and continued for three days after weaning similarly the control group was injected with two mL of a saline solution. Naloxone treated sows showed estrus 88.8 Ó 6.2 hours after weaning (P<0.1), control sows estrus was evident 102.37 Ó 7.2 hours after weaning. Duration of estrus in treated and nontreated was 85.6 Ó 3.8 and 42.6 Ó 3.7 hours, respectively. Prolactin levels decreased rapidly after weaning in both groups, but Prolactin plasma levels in naloxone treated sows were below control levels (15 Ó 2 and 7 Ó 0.3 Ng, respectively; P<0.1). Behaviour scores showed that naloxone treated sows accepted mounting with a significant reduction in aggressive behaviour as compared with controls. It was concluded that opioids are important modulators of sow sexual behaviour.
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