Effects of short- and long-term fasting on the ovarian axis and reproductive performance of rabbits does

To assess the impact of acute nutritional challenges on reproductive performance, 116 rabbit does were randomly assigned to either “control” or two “fasting” groups. In the control group, the does were fed ad libitum (AL) while in the treated groups the animals were fasted for 24 (STF) or 48 h (LTF) before artificial insemination (AI). In both treated groups, the rabbits were re-feed 2 hours before AI, which was performed at day 11 post partum (pp) in STF does and at day 32 or 55 pp in LTF does following GnRH injection to induce ovulation. In a parallel experiment, blood samples were collected from 10 rabbits/groups by catheterization of the central ear vein at 15 min intervals for 4 h prior and after GnRH, then at hourly intervals for other 4 h, and again 24 and 48 h later to measure LH, estradiol-17b? and leptin. The expression of estradiol-17b receptors (ER) was evaluated by immunohistochemistry in the hypothalamus and anterior pituitary obtained from both control and treated rabbits after 24 and 48 h of fasting. The 24-h long fasting reduced receptivity (55.8 vs. 70.9%), fertility rate (42.8 vs. 59.2%) especially in does with parity =4 (50 vs. 80%; P=0.05), and kits born alive (6.6 vs. 7.7). Also the does fasted for 48 h, showed lower fertility (31.2 vs. 52,6 %) and litter size at birth (8.7 vs. 9.6) than controls. Following GnRH injection, the LH peak was higher in AL and STF than in LTF does (Mean ± SEM, 39.3±17.04 vs. 31.3±3.39 and 12.2±1.23 ng/ml, respectively). Estradiol-17b showed higher pulse frequency and amplitude in AL than in STF and LTF does. Toward the end of fasting, mean plasma leptin concentrations were lower (P£0.01) in both STF and LTF does than in control rabbits (0.82±0.19, 1.20±0.1, and 2.32±0.33 ng/ml, respectively), but then gradually increased in both treated groups following re-alimentation. Compared to controls or STF does, ER-like immunoreactivity decreased in the ventromedial nucleus of LTF rabbits, but increased in the medial preoptic area. ER expression was greatly reduced in the anterior pituitary of LTF does.