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.