Genetic and non-genetic effects on plasma insulin-like growth factor I (IGF-1) and production traits in Angus cattle

Plasma insulin-like growth factor-1 concentration (IGF-I) was measured at weaning on 1756 Angus beef cattle from herds in the New England and surrounding regions of NSW to estimate the heritability of IGF-I and phenotypic and genetic correlations with other production traits. Average IGF-I was 253.9 ng/mL measured at the mean age of 237 days. IGF-I had a moderate heritability of 0.36. Phenotypic correlations were essentially zero between IGF-I and birth weight, 200-day weight and pre-weaning average daily gain. IGF-I concentration was not genetically correlated with birth weight and scanned eye muscle area, but was correlated with both 200-day weight and average daily gain with genetic correlations of -0.40 and -0.52, respectively. Daily feed intake and IGF-I concentration were estimated to have a negative genetic correlation of -0.33. Scanned rump and rib fat depth, intramuscular fat content and residual feed intake were all estimated to have positive genetic correlations between 0.31 and 0.33 with IGF-I concentration. These estimates indicate that plasma IGF-I concentration measured in seedstock herds at weaning will be a suitable trait to indirectly select for fat and feed efficiency traits.