Glucose-dependent insulin response and milk production in heifers within a segregating resource family population

An experiment was initiated to evaluate the glucosedependent insulin response in relation to milk production in F-2 crossbred cattle with respect to secretion type (Holstein) and accretion type (Charolais). For this purpose, F-2 offspring were generated by mating Charolais bulls with German Holstein cows and a following intercross of the F-2 individuals. In 52 dairy heifers of 5 F-2 half-sib families, glucose-dependent insulin responses were investigated during first lactation to test the hypothesis that the different genetic disposition for milk production within the F-2 population would affect the insulin response to glucose. Heifers received intravenous glucose infusions (1g/kg of BW0.75) 10 d before, and 30 and 100 d after parturition. Blood samples were taken before and at 7, 14, 21, and 28 min after glucose challenge. Glucose and insulin concentrations were measured in blood, and glucose half-life as well as areas under the curve for glucose (AUC(gluc)) and insulin (AUC(ins)) were calculated. Milk yield was low but differed among F2 families. Before parturition, insulin concentrations after glucose challenge showed no between-family differences for AUCi,s. In contrast, on d 30 and 100 of lactation, glucose half-life and AUCins differed among families. Calculated correlations revealed a significant negative relationship between AUC(ins), and milk yield as well as glucose half-life on d 30 and 100 of lactation. In conclusion, milk production as well as the glucose-dependent insulin response of F-2 Charolais x German Holstein crossbred dairy heifers differed between half-sib families, with both parameters displaying an inverse relation to each other.