Strain differences in lean : fat partitioning were typified by a marked contrast in a lean growth index giving equal but opposite emphasis to the weights of protein and fat, in line with previous publications. Strains showed characteristic differences in blood metabolites which did not necessarily reflect genetic variations within a strain and correlated responses to within-breed selection for changes in body composition. High repeatabilities of blood metabolites within a strain were found for pasture-fed lambs aged between 5 and 14 months for samples collected on the same day following overnight fasts of 20 vs 24 hours, but were lower for samples taken from fasted animals at different ages. Between-age within- strain repeatabilities (averaged across two trials) were moderate for plasma urea (0.24) creatinine (0.38) and non-esterified fatty acids (0.18), but low for beta-hydroxybutyrate (0.09). Similar moderate heritability estimates were found for urea and creatinine. Although standard errors were very high for this small dataset based on only 12 sires, estimates for carcass composition were in broad agreement with other more reliable published values. Also in line with other results, sire-progeny variations in urea and beta- hydroxybutyrate were more positively related to carcass protein than carcass fat, while the reverse was true for creatinine. Metabolically contrasting pairs of metabolites showed potentially useful predictive associations with sire- progeny variations in protein:fat partitioning.
Proceedings of the New Zealand Society of Animal Production, Volume 56, , 180-183, 1996
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