Association between the GHR, GHRHR, and IGF1 gene polymorphisms and milk yield and quality traits in Sarda sheep

The growth hormone receptor (GHR), the growth hormone releasing hormone receptor (GHRHR), and the insulin-like growth factor 1 (IGF1) genes are known to modulate growth, reproduction, and lactation traits in livestock. The aim of the current work was to investigate if the variation of the sheep GHR, GHRHR, and IGF1 genes is associated with milk yield and quality traits. Three hundred eighty dairy Sarda sheep were genotyped for 36 single nucleotide polymorphisms (SNP) mapping to these 3 loci, and records for milk yield and daily fat and protein yield, as well as for fat, protein, casein, lactose, and milk urea contents, pH, somatic cell score, logarithmic bacterial count, and milk energy were obtained. The linkage disequilibrium analysis was performed only for GHR, as both GHRHR and IGF1 had only 1 polymorphic SNP. Haplotype analysis revealed the existence of 7 haplotype blocks in GHR. Two haplotype blocks, including part of the intron 1 and the upstream region, were clearly separated from the remaining 5 blocks by SNP rs412986330, which may be a recombination hotspot. The latter 5 blocks were contiguous, spanning from intron 2 to exon 10. Statistical analysis revealed that the GHR polymorphism is significantly associated with milk traits for daily fat and protein yield and fat, milk urea, and lactose content. Moreover, variation in IGF1 was associated with milk protein and casein content. Data generated in this research provide new insights into the allelic effects of the ovine GHRHR, GHR, and IGF1 genes on milk production and quality traits, information that may be useful in gene-assisted selection programs.