The effects of a transient doe-litter separation on plasma prolactin, FSH and oestradiol concentrations, as well as the effect on LH response to exogenous GnRH administered at the time of artificial insemination, were determined in nursing rabbits. The effects on fertility, and litter size after parturition, as well as litter survival after doe-litter separation, were also studied. Control does (n = 12) had free access to nursing, whereas biostimulated does (n = 12) were separated from their litters for 48 h before artificial insemination. Plasma prolactin concentrations were decreased 24 h after the doe-litter separation (P < 0.05). The response of prolactin to suckling 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 insemination. Exogenous GnRH administered at the time of artificial insemination caused a greater LH response in does previously separated from their litters during 48 h (P < 0.01). The transient doe-litter separation did not affect plasma FSH concentrations, fertility, litter size or litter survival. These results suggest that a transient separation of nursing does from their litters before artificial insemination results in a decrease in plasma prolactin concentrations that could promote growth of follicular waves, and high steroidogenesis activity, leading to increased oestradiol concentrations and inducing higher sensitivity of the pituitary gland to exogenous GnRH. These findings associated to the absence of suckling episodes would lead to higher LH response and, therefore, exert a major effect on fertility.
Calcium Availability Influences Litter Size and Sex Ratio in White-Footed Mice (Peromyscus leucopus)