Pituitary and ovarian response to transient doe-litter separation in nursing rabbits

The effects of a transient doe-litter separation on plasma prolactin, FSH a nd oestradiol concentrations, as well as the effect on LH response to exoge nous GnRH administered at the time of artificial insemination, were determi ned in nursing rabbits. The effects on fertility, and litter size after par turition, as well as litter survival after doe-litter separation, were also studied. Control does (n = 12) had free access to nursing, whereas biostim ulated does (n = 12) were separated from their litters for 48 h before arti ficial insemination. Plasma prolactin concentrations were decreased 24 h af ter the doe-litter separation (P < 0.05). The response of prolactin to suck ling reached 10 times the basal values measured on day 10 after parturition (P < 0.0001). Increased oestradiol concentrations were found during the 48 h after the doe-litter separation: at 0 h, before artificial insemination (P < 0.0001), 1.0-2.0 h after artificial insemination (P < 0.001), at 2.5 h (P < 0.05), 3.0 h (P < 0.01), and at 3.5 h (P < 0.05) after artificial ins emination. Exogenous GnRH administered at the time of artificial inseminati on caused a greater LH response in does previously separated from their lit ters during 48 h (P < 0.01). The transient doe-litter separation did not af fect plasma FSH concentrations, fertility, litter size or litter survival. These results suggest that a transient separation of nursing does from thei r litters before artificial insemination results in a decrease in plasma pr olactin concentrations that could promote growth of follicular waves, and h igh steroidogenesis activity, leading to increased oestradiol concentration s and inducing higher sensitivity of the pituitary gland to exogenous GnRH. These findings associated to the absence of suckling episodes would lead t o higher LH response and, therefore, exert a major effect on fertility.