INFLUENCE OF PROLACTIN ON FETAL SURVIVAL IN RABBIT DOES

Experiments were conducted to assess the influence of prolactin levels on foetal survival in pregnant does. All the females were mated withi n 12 h following parturition (Day 0), and slaughtered on Day 28 to stu dy reproductive performance. In Experiment 1, lactation was terminated at birth and females in the treated group (Group P, n = 34) were inje cted with 1 mg of ovine prolactin daily from Day 7 to Day 21. Females in the control group (Group CP, n = 31) received no prolactin. On Day 16, the ovine prolactin concentration in Group P was 32.5 ng ml-1. The concentration of rabbit prolactin was higher and the serum level of p rogesterone was lower in Group P than in Group CP on Day 16 (P < 0.01) . The ovulation rate was similar in both groups but late foetal mortal ity (> Day 15) was significantly higher in Group P (24.5% vs. 10.6%; P < 0.01). In Experiment 2, females were allowed to suckle seven young and received 1 mg of bromocriptine daily from Day 14 to Day 18 (Group B, n = 34). Females in the control group (Group CB, n = 31) received n o bromocriptine. The concentration of prolactin was lower in Group B t han in Group CB on Days 14 and 18 (P < 0.01), and the concentration of progesterone was higher in Group B on Day 18 (P < 0.01). The ovulatio n rate and early and late foetal mortality were similar in both groups but the number of resorbed foetuses was higher in Group B than in Gro up CB (1 vs. 0.5; P < 0.05). These results suggest that hyperprolactin aemia during lactation is responsible for the reduced progesterone con centration and the increased late foetal mortality observed in pregnan t lactating does. However, short-term suppression of prolactin release after suckling does not improve foetal survival.