BLOOD METABOLITE CONCENTRATIONS IN HEREFORD X FRIESIAN OFFSPRING OF BULLS SELECTED FOR LEAN GROWTH-RATE AND LEAN FOOD CONVERSION EFFICIENCY

Blood samples were taken at intervals from 5 to 13.5 months of age on 352 Hereford x Friesian calves undergoing a postweaning performance test. Up to 5 samples were taken on each animal. The calves were sired by bulls selected for either Lean Growth Rate (LGR) or Lean Food Conversion Ratio (LFCR), or by unselected bulls acting as controls. Measurements taken on the blood samples were concentrations of total blood protein, albumin, urea, beta-hydroxy butyrate, glucose and haemoglobin. Albumin was subtracted from total blood protein to give globulin concentrations. Significant between line differences were observed only for globulin, with the LGR calves having higher concentrations and the LFCR calves lower concentrations than the control calves. Heritabilities for protein, albumin, globulin, urea, beta-hydroxy butyrate, glucose and haemoglobin concentrations were 0.18, 0.09, 0.14, 0.12, 0.00, 0.07 and 0.23, respectively. All metabolites, except beta-hydroxy butyrate, showed a significant repeatability between successive measurements taken on indivudual animals, but for haemoglobin concentrations the estimated repeatability was lower than the heritability. Genetic correlations between the metabolite concentrations and LGR and LFCR mirrored the LGR, LFCR and control line means for urea, glucose and haemoglobin concentrations, but no correlations were significantly different from zero. No strong relationships were observed between performance traits and any of the blood measurements, and only for carcass composition traits did indexes of blood measurements account for more than 0.01 of the total variation.