The effect of change and level of nutrition on the reproductive performance of group-fed dairy heifers

Abstract

ABSTRACTOne hundred and sixty Friesian heifers were allocated to two groups 8 or 9 weeks before artificial insemination and group-fed to gain live weight at 0·8 or 0·3 kg/day. Half the heifers of each group were moved to the other group 2 weeks before first insemination. All heifers received two intramuscular injections of prostaglandin (cloprostenol) 11 days apart, followed by inseminations at 72 and 96 h after the second injection.The feeding regimes applied did not significantly affect the fertility of groups of heifers as measured by pregnancy rates to fixed-time or all inseminations. There were significant differences between pregnant and nonpregnant heifers within groups where changes in feeding levels were imposed (P<0·1 to P<0·01). Heifers whose growth rate was most severely checked, or whose body condition deteriorated relative to others in the group, were less fertile. For heifers changed from the low to the high plane of nutrition, those experiencing the greater increase in growth rate and body condition were more fertile than others.No relationship was found between live-weight change, plasma glucose concentrations and fertility. In a second trial 158 Friesian heifers received two injections of cloprostenol 11 days apart, followed by inseminations at 72 and 96 h after the second injection. After the fixed-time inseminations the heifers were divided into two groups and were group-fed to gain live weight at 0·8 and 04 kg per head per day. Although the mean live-weight gain of the high group was significantly higher than that of the lower group (P<0·001), the overall pregnancy rates were not significantly different.