Longitudinal analysis of the effects of IGF1-SnaBI genotypes on the growth curve of Angus bull calves

The Insulin Growth Factor 1 (IGF1) has been proposed as a candidate gene for growth related traits as it plays a central role in growth and development of mammals. A relationship between serum IGF1 concentration and different growth traits in cattle has been documented. Furthermore, the IGF1-SnaBI SNP in the gene promoter region influences gene expression and IGF1 blood level. The current research was conducted to perform a genetic analysis of longitudinal data for growth curves through the evaluation of the influence of IGF1-SnaBI genotypes on the growth curve of beef cattle during highly anabolic stages. Data were taken on 275 Angus bull calves on two consecutive years, in two commercial cow-calf operations. Calves were weighed at birth, at weaning, and at 3 to 4 times before the year of age. A random regression animal model was employed for the analysis. Fixed effects were age of dam, herd-year, and age of calf (linear and quadratic terms nested within IGF1-SnaBI genotype). Random effects were age at measure (linear and a quadratic terms nested within animal). The analysis showed significant differences (P<0.01) in the growth curves at ages in between 66 and 291 days for the IGF1-SnaBI genotypes. At 210 days of age, the effect of substituting a T by a C was estimated to be 5.21 kg. These results suggest that the effect of IGF1-SnaBI over growth in cattle take place mostly before puberty.