Genetic parameters of growth in dairy cattle and associations between growth and health traits.

Body weight (BW) observations on dairy cattle taken on average 35 times between birth and 1,000 d of life were used to estimate daily heritabilities and predict daily breeding values for both pregnancy-adjusted BW (PABW) and growth rate. Daily heritabilities for PABW were moderate to high, ranging from 0.41 (+/-0.027) to 0.82 (+/-0.041). Daily heritabilities for growth rate were high (>0.68 +/- 0.034). The genetic association between various health events, including mastitis and lameness, and weight and growth was investigated by regressing the incidence of health events on breeding values for weight at birth, weaning, calving, and growth rate at 56 d after calving, growth rate at 110 d after calving, and maximum growth rate. Growth at weaning was the only BW measure to significantly affect mastitis (r(g) = 0.24), indicating that cows growing faster at weaning are more prone to mastitis. Increased weight (r(g) = 0.65) and growth rate at weaning (r(g) = 0.38) and increased maximum growth rate (r(g) = 0.71) all contributed to increased feet disorders. The only significant negative genetic association was obtained between reproduction and weight at calving (r(g) = -0.61).