Characterization of biological types of cattle by the blood levels of creatine and creatinine.
Data were analysed on 831 bulls slaughtered at 12 months of age, and on 102 AI sires. The 831 young bulls belonged to 4 biological types: double muscled (DM) Belgian Blue [Central and Upper Belgium] (n = 567); conventionally muscled Belgian Blue (n =164); Belgian Blue (DM) × Friesian (n = 82); Belgian Blue (DM) × Red and White (n = 18). Among the 102 AI sires, 45 were of the Belgian Blue breed (DM type), 12 were of the same breed but classified as dual-purpose, 31 were of the Friesian breed, and 14 of the Red and White [Campine Red Pied] breed. The characters studied were dressing percentage, percentage of lean in the 7th rib cut, and the plasma and erythrocyte creatine and creatinine. For the AI sires, only the blood characters were studied. The characterisation of these biological types, within each trait, was carried out by comparison of means, by regression analysis, and by discriminant or canonical analyses. All these approaches showed the double-muscled animals to be quite distinct from the other types, and that among the latter, identification of breed type from a blood sample was also possible. Across biological types, the blood characters had good predictive value for carcass composition. This was not true within biological types. Although genetic correlations between the blood constituents and dressing percentage were significant, they were not large enough to justify the use of these blood criteria as an aid to selection for better muscling.