A genetic analysis of the concentrations of blood metabolites and their relationships with age and liveweight gain in young British Friesian bulls

Blood samples were taken from 428 young British Friesian bulls, the sons of 72 sires, between 3 and 15 months of age. The concentrations of blood glucose and haemoglobin and serum cholesterol, urea, albumin, globulin, inorganic phosphate, Ca, Mg, Na, K and Cu were measured and correlated with age and growth rate.Most of the constituents showed highly significant but small changes in concentration with age. The largest changes occurred in the concentrations of urea, albumin and haemoglobin which increased as bulls reached maturity. The concentrations of urea, albumin and globulin were also lower and concentrations of glucose, inorganic phosphate, Ca and K higher than usually occur in older cattle.Highest estimates of heritability, based on the mean of 3 samples, were for K and globulin (> 0.6) and for haemoglobin, cholesterol, inorganic phosphate, Cu and glucose (0.4–0.6). Phenotypic correlations between 0.2 and 0.4 occurred with growth rate for albumin and glucose between 24 and 35 weeks and with body weight for albumin between 27 and 50 weeks of age; however, the phenotypic correlations with average growth rate up to 53 weeks were only 0.15 and 0.07 for albumin and glucose, respectively. Genetic correlations with growth rate were also determined, but standard errors were large.