95 THE USE OF A REARING-FASTING PROGRAM AS AN ALTERNATIVE BIO-STIMULATION METHOD TO HORMONAL EQUINE CHORIONIC GONADOTROPIN TREATMENT TO CONTROL THE EMBRYO RECOVERY OF RABBIT FEMALES

Abstract

The aim of this study was to investigate the effect of a rearing-fasting program as an alternative bio-stimulation method to hormonal eCG treatments on the embryo recovery of rabbit females. A total number of 119 nulliparous New Zealand White rabbit females at 14 wk old were randomly allocated into 1 of the following 3 groups before the first insemination at 18 weeks old: control group (n = 39), females were fed ad libitum until the first insemination; eCG group (n = 34), females were fed ad libitum and treated with 50 IU of eCG hormone SC 60 h before the first insemination; and r-FP group (n = 46), females were fasted 3 days per week during 3 wk and then allowed to feed ad libitum 1 wk before the first insemination. Sexual receptivity was evaluated for each group on the day of insemination. Only receptive females (74/119) were artificially inseminated and immediately were induced for ovulation by intramuscular injection with gonadotropin-releasing hormone analogue (0.8 μg of buserelin acetate). In 23 receptive females, embryos were recovered postmortem at 72 h post-insemination in each group (n = 7, 9, and 7 in control, eCG, and r-FP groups, respectively). The number of recent corpora lutea on both ovaries (CL), the number of hemorrhagic follicles (HF), the recovery rate (RR), the number of normal embryos recovered in receptive females (NE), the embryo donor rate (DR), and the blastocyst rate (BR) were recorded for all groups. A General Linear Model was performed to analyse CL, HF, and NE, and a chi-square test was used to compare sexual receptivity, RR, DR, and BR in the experimental groups (eCG, r-FP, and control). A significant increase in sexual receptivity was observed in eCG group compared with the other groups (82 v. 50 and 59%; eCG v. r-FP and control groups, respectively; P < 0.05). The CL was significantly (P < 0.05) higher in eCG group (13.8) than in r-FP and control groups (9.1 and 10.3, respectively). However, high incidence of HF was also observed in the eCG group (3.9 v. 0.9 and 1.3 in eCG v. r-FP and control, respectively; P < 0.05). The RR was significantly (P < 0.05) higher in r-FP group (64.1%) when compared with eCG and control groups (38.7 and 20.8%, respectively). The DR was significantly higher for r-FP group compared with the control (100% v. 42.9%, respectively; P < 0.05) and intermediate for eCG group (77.8%). No significant differences were observed in the NE (6.1, 5.7, and 5.0 in eCG, r-FP, and control, respectively). The BR significantly (P < 0.05) decreased in eCG group when compared with r-FP or control groups (4.7% v. 60.0 or 53.3%, respectively). Our results indicated that a rearing-fasting program followed by 1 wk of feed flushing before the first insemination of nulliparous rabbit females could be recommended as an efficient bio-stimulation method to control embryo recovery. However, these results need to be confirmed in a larger scale and several reproductive cycles before widely applied.