Polymorphism of the Insulin-like growth factor 1 receptor gene (IGF1R/e10/MspI and IGF1R/e16/RsaI) in four dairy breeds and its association with milk traits

Studying candidate genes for significant economic traits could be directly applied in a search for quantitative trait loci. There is growing evidence that the IGF-I/IGF-1R signaling pathway can be involved in mammary gland development and milk synthesis control. The bovine Insulin-like growth factor 1 receptor gene encodes a transmembrane ligand-activated tyrosine protein kinase. The presence of two synonymous mutations (IGF1R/e10/MspI and IGF1R/e16/RsaI) have been validated in 4 dairy breeds (Polish Holstein-Friesian, Holstein-Friesian, Montbeliarde and Jersey). A total of 1167 blood samples were genotyped. Five milk performance traits, i.e., milk yield (MY), fat yield (FY), protein yield (PY), fat percentage (F%), and protein percentage (P%) were used in the association analysis. The data for the full 305-day milk production (1st, 2nd and 3rd lactation, collected between 2007 and 2014) were obtained from the official farm records. The TT genotype of both polymorphisms was found to be associated with the highest yields (milk yield - MY, fat yield - FY and protein yield - PY), while the lowest values were recorded for the CC genotype (P≤0.01). In order to confirm or refute the association found, statistical analysis of the combined genotypes was also performed. Irrespective of breed and lactation order, cows with the TT/TT genotype combination were usually characterized by the highest milk, fat and protein yields, as opposed to the least favorable CC/CC combination. As regards the milk yield, the differences were in the range of 2000 kg (MO) to 3000 kg per lactation (PHF, HF) (P≤0.01). Significant differences at the level of 80÷130 kg for FY and 50÷100 kg for PY were also recorded (P≤0.01). No statistical differences in fat and protein content were found. In light of these results, the IGF1R gene can be proposed as a candidate gene for milk traits in cattle.