Effect of different dietary energy level intakes on efficiency of estrus synchronization and fertility in Mashona goat does

Abstract

The objective of the study was to determine the effects of three dietary energy levels: 0.27 (low level: LL); 0.53 (medium level: ML), and 1.06 (high level: HL) MJ ME kg −1 W 0.75 on estrus synchronization and fertility in Mashona goat does. Forty-five multiparous Mashona goat does of average bodyweight 19.9±2.5 kg were randomly allocated in equal numbers to the three dietary energy levels. The diets were made from a complete feed ration providing 9.83 MJ ME kg −1 DM and 15.5% CP kg −1 DM. Does were fed initially during a 60-day pre-synchronization period, and blood samples were collected twice a week for the determination of plasma progesterone concentrations to ascertain ovarian activity. Intramuscular injections of cloprostenol (100 μg each) were administered 11 days apart. Immediately after the second injection of cloprostenol, three fertile bucks were introduced to the does and were left with the does for 21 days. The does were maintained on their dietary treatments throughout gestation except for those does in the LL treatment. Pregnancy was diagnosed 90 days post-mating using an ultrasound scanner. After pregnancy diagnosis, does on the LL treatment were randomly allocated to ML ( n=7) and HL ( n=8) treatments. During the pre-synchronization period, does on the LL treatment lost 12.3% whereas those on ML and HL treatments gained 2.1 and 28.8% of their initial bodymasses, respectively. The proportion of does exhibiting overt estrus within 96 h after the last cloprostenol injection was significantly lower ( P<0.05) for does on the LL treatment (60%) than for those on ML (93%) or HL (100%) treatments, respectively. However, based on plasma progesterone concentrations, the percentage of does on the LL treatment that exhibited ovarian cycles was numerically lower than that of does that were bred (40 versus 73%). Conception, fecundity and twinning rates were significantly lower ( P<0.05) on the LL treatment than on the ML and HL treatments. These results indicate that feeding Mashona goat does 0.27 MJ ME kg −1 W 0.75 compared to 0.53 and 1.06 MJ ME kg −1 W 0.75 reduces the expression of estrus, conception, fecundity and twinning rates, and that feeding 0.53 MJ ME kg −1 W 0.75 suffices for optimum reproduction. In addition, the results suggest that cloprostenol administration may induce ovarian cycles in reproductively quiescent does on dietary energy restriction.