Association of the Leu127 variant of the bovine growth hormone (bGH) gene with increased yield of milk, fat, and protein in Australian Holstein-Friesians

Abstract

The occurrence of the Leu¹²⁷/Val¹²⁷ variants of the bovine growth hormone (bGH) gene and their effect on milk production traits was investigated in Australian Holstein-Friesian cattle. Animals were genotyped for the Leu¹²⁷/Val¹²⁷ variants, with RFLP methodology, using PCR and AluI digestion of PCR products (AluI-RFLP). Alleles Leu¹²⁷ and Val¹²⁷ occurred with frequencies of 82% and 18%, respectively. The quantitative effect of this polymorphic site on milk-production traits was estimated from lactation data and test-day data. Results from the 2 data sets consistently showed that the Leu¹²⁷ allele is associated with higher production of milk, fat, and protein and is dominant to Val¹²⁷. The average effects of the gene substitution are 95 L for milk yield, 7 kg for fat yield, and 3 kg for protein yield per lactation. This locus may be directly responsible for quantitative variation or it may be a marker for a closely linked quantitative trait locus (QTL) for milk-production traits in Australian dairy cattle. In either case, it will be useful as an aid to selection for improvement of milk production traits. As the Leu¹²⁷ allele is dominant, selection of AI sires homozygous for the Leu¹²⁷ allele (Leu¹²⁷/Leu¹²⁷) will result in maximum benefit without the need for genotyping cows.