Mutation in exon 5 of bovine prolactin gene is not associated with milk traits in Holstein bulls.

The prolactin hormone, PRL, plays a critical role in lactation. This hormone is, primarily responsible for the synthesis of milk proteins, lactose, and lipids, all major components of milk. In addition, PRL has been shown to directly stimulate insulin-like growth factor-I binding proteins, epidermal growth factor, a glycolysated mucin, parathyroid-like peptide, and PRL-inducible proteins in normal and neoplasmic tissue. The objectives of this research were to identify mutation in exon 5 of bovine PRL gene and to establish association between observed mutation and milk traits in Holstein bulls DNA was extracted from semen of 1100 Holtsein bulls provided by Semex-Alliance (Guelph, Canada). A mixed model was used to study association between alleles and milk, protein and fat yields. In this model, herd, year, season, parity, lactation, age classes, month of lactation were fixed effects and permanent environment, animal and residual effects were considered as random effects. Using BESS-Scan Mutation Detection and localization Kit (Epicentre Technologies), a mutation was found in the fifth exon of the PRL gene. By DNA sequencing, a A to G transition was identified at the 718 amino acid of the protein. In our population, allelic frequencies of the A and G alleles were 0.34 and 0.66, respectively. Statistical analysis showed no significant effect of PRL polymorphism at the exon 5 on lactation traits. In conclusion, the PRL polymorphism found in the fifth exon was not associated with lactation traits of Holtein bulls. This polymorphism is, thus, not a tool of choice for using in breeding programs. This research was supported by Belgian Ministery of Agriculture grant 5859 and Semex Alliance, Guelph, Canada.