Relationships between dietary supplementation, blood metabolite concentrations and fertility in Boran and Boran x Friesian Heifers

Forty-three Boran and 46 Boran x Friesian heifers, weaned at eight months of age, were allocated to either receive dietary supplementation (16% crude protein and 10.8 MJ/kg dM energy) during the dry season or to serve as controls. Post weaning body weight measurements were taken at monthly intervals and two sets of blood samples were collected from all heifers each during the wet season, between beginning and end of supplementation and between beginning of supplementation and beginning of mating period. Plasma samples were used for the determination of total protein, albumin, globulin, blood urea nitrogen (BUN) and glucose concentrations. Breeding bulls were introduced when heifers attained 18 months of age and mating lasted for three months. Body weight gains from weaning to beginning of mating were positive in all treatment groups, but was higher (P0.001) in supplemented than in control heifers (197.1 plus or minus 13.1 vs 121.3 plus or minus 10.4 g/d) and in Boran x Friesian than in boran heifers (179.6 plus or minus 95.9 vs 137.6 plus or minus 48.7 g/d). During the dry season, growth rate was faster (P0.001) in supplemented than in control heifers (122.0 plus or minus 6.8 vs 49.8 plus or minus 6.7 g/d) and in boran x Friesian than in Boran heifers (99.3 plus or minus 10.4 vs 71.6 plus or minus 6.6 g/d). by the end of the mating period, pregnancy rate was higher (P0.001)in the supplemented (70%) than in the control (35%) group. Similarly, more percentage (P0.01) of Boran x friesian heifers became pregnant than the boran heifers. the patterns of changes in concentrations of blood metabolites with age were not consistent in both genotypes. There were no nutritional effects and genotype differences in mean concentrations of plasma total protein, albumin, albumin/globulin ratio and glucose.