Genetic and phenotypic relationships between physiological traits and performance test traits in sheep

Abstract

151 performance-tested rams, progeny of 31 sires, from lines of Texel-Oxford sheep divergently selected for carcass lean content were studied. At the end of the test, the animals were fed at 08.00 h and then fasted for 54 h. Blood samples were taken during feeding and fasting. Under normal feeding, estimates of h2 were higher for traits associated with protein metabolism, creatinine, urea and insulin-like growth factor-I (IGF-I) than for traits associated with lipid and energy metabolism, beta -hydroxybutyrate, non-esterified fatty acids, triglyceride and glucose. beta -Hydroxybutyrate, creatinine and IGF-I were moderately correlated with live weight and muscle depth, and urea and IGF-I were significantly correlated with backfat depth. Significant correlations were found for beta -hydroxybutyrate and IGF-I with predicted carcass lean weight and for urea with predicted carcass lean content. The results also showed that measurements of physiological traits during fasting may not be required for the prediction of genetic merit using physiological traits, as genetic correlations between the traits during feeding and fasting were high, except for glucose.