Abstract:
Nutrition influences postpartum ovarian activity but the effects of pre and postpartum feeding on metabolte and hormonal changes and their subsequent influence on reproductive performance remains unclear. This study attempted to explain effects of nutrition on these changes and their ultimate impact on reproductive performance of lactating cows. Forty in-calf cows comprising 20 Friesians and 20 Sahiwals were randomly assigned to 5 dietary groups of 4 cows per breed. Upon calving, cows were fed a basal diet of Rhodes grass pasture and supplemented with dairy meal concentrate at the rate of 0, 1, 2, 3, and 4 kgs per day. Body weight and condition, milk yield and composition (% BF, % P, %SNF, density and freezing point), hormonal (progesterone and IGF-1) and metabolites (glucose, urea, NEFA and albumin) levels were measured weekly. The cows were observed for heat, inseminated and monitored up to the next calving. Days to
commencement of luteal activity, insemination and calving intervals were also determined. Data was subjected to correlation, general linear models, repeated measures, principal component and regression analysis procedures of SAS. Sahiwals lost less body condition (-0.1 vs -0.4), commenced luteal activity (6 vs 10 weeks) and were inseminated (10 vs 14 weeks) earlier than Friesians. In both breeds, reduced levels of NEFA and threshold levels of 3ng/ml for progesterone coincided with days to commencement of luteal activity and insemination. Only 76% of the cows exhibited heat signs and were served, with 56% of them eventually calving. Friesians attained higher peak milk yield per week (88.9±1.7 vs 68.3±1.6 lts) than Sahiwals. Milk components and reproductive parameters were positively correlated in Friesian but negatively associated in Sahiwals. Services per conception for Friesians were 1.53 compared to Sahiwals 2.42. There were positive correlations (r=0.29) between days to luteal activity and insemination and negative correlations (r=-0.21) with calving intervals. Feeding levels had no effect on days to commencement of luteal activity but influenced metabolites and hormonal levels, particularly glucose and progesterone. Cows that calved expressed heat earlier (70.5±13.4 vs 96.8±21.5 days), had higher (p<0.05) mean levels of progesterone (3.78±0.6 vs 3.1±0.42 ng/ml) than those not calving. Cows conceived when IGF-1 levels exceeded 25ng/ml threshold levels. Nutrition had an effect on progesterone, IGF-1, glucose and NEFA that proved suitable predictors of the subsequent reproductive performance of cows after parturition.
