Hormone profiles and nest-building behavior during the periparturient period in rabbit does.

This study was done to elucidate the relationship between the hormones beta-estradiol, progesterone, prolactin and beta-endorphin and nest-building behavior in rabbit does during the periparturient period. Beta-estradiol increased as parturition approached with a significant increase starting 2 days before parturition (day -2). Progesterone decreased with the progress of gestation, but a significant decrease was observed starting on day -2. Prolactin concentration started to increase on day -2 prepartum but a significant increase in prolactin concentration was not noted until the last day of pregnancy. The concentration of beta-endorphin was highly variable during the sampling period and could not be correlated with the other hormones or nest-building behavior. To assess the role of prolactin in nest-building behavior, groups of rabbits were treated with bromocryptine, bromocryptine plus prolactin or saline (controls). Treatment with 4 mg bromocryptine or 4 mg bromocryptine + 1.5 mg bovine prolactin on days 25 and 27 of pregnancy did not affect the number of live kits born or the gestation length. The mean nest scores, a measure of the nest quality, were not affected by bromocryptine treatment, but treatment with bromocryptine plus prolactin resulted in lower nest scores (P < 0.05). Injection of 8 mg bromocryptine from day 28 of gestation to kindling resulted in an extended gestation (P < 0.05). Injection of 4 or 8 mg bromocryptine resulted in fewer live kits born (P < 0.05), reduced nest scores (P < 0.01) and blocked milk production, as determined from the palpable mammary tissue. These results indicate that prolactin has less influence on nest-building behavior than on milk production. The hormones most likely to influence nest building are beta-estradiol and progesterone because the levels of these hormones started to change at the time when the rabbits started to prepare nests. Further study is required to determine the influence of these hormones on nest-building behavior.