Association of a genetic marker with blood serum insulin-like growth factor-I concentration and growth traits in Angus cattle

The objective of this research was to evaluate a biallelic genetic marker i dentified in the first promoter region of the bovine IGF-I gene. The point mutation was identified as a T-to-C transition by sequencing the polymorphi c fragments. A PCR-RFLP procedure was developed for determining the marker genotypes. Marker genotypes were determined for 760 Angus calves from diver gent lines that were created by selection for high or low serum IGF-I conce ntration (allele A: 63.9%, B: 36.1%). Data were analyzed using the multiple -trait derivative-free restricted maximum likelihood computer programs with animal models. The full animal model included fixed; effects of marker gen otype, birth year, season of birth, sex, age of dam, and selection line; ra ndom effects of animal, maternal genetic, and maternal permanent environmen tal effects; and a covariate for age of calf. Traits analyzed included bloo d serum IGF-I concentrations on d 28, 42, and 56 of the postweaning test, m ean IGF-I concentration, birth weight, weaning weight, on-test weight, off- test weight, off-test hip height, postweaning gain, and weight gain during the 20-d period immediately after weaning. Results from the analysis across selection lines showed a significant association of the BE genotype with h igher weight gain during the first 20 d after weaning and a slight dominanc e effect of the marker on postweaning gain. Analysis within the low IGF-I l ine also showed a significant association of the BE genotype with higher we ight gain during the first 20 d after weaning and with on-test weight, alth ough analysis within the high IGF-I line did not show any significant assoc iation. The associated effects of the marker need to be verified in other c attle populations.