A TG-repeat polymorphism in the 5′-noncoding region of the goat growth hormone receptor gene and search for its association with milk production traits

A variable TG-repeat polymorphism was found in the goat growth hormone receptor (GHR) gene 5′-noncoding region. In total 235 goats belonging to two dairy breeds were genotyped, 10 alleles of the GHR gene were detected. The length of the repeat region variants (alleles) was from 305 to 346 bp. Among the 10 alleles identified, eight occurred in homozygous systems. The frequency of the homozygous genotypes was 0.25 for the Polish White Improved breed and 0.28 for the Polish Fawn Improved breed. The mean heterozygosity (H) and polymorphic content coefficients (PIC) at this locus were similar for both breeds. The association of the TG-repeat variants was studied with milk production traits in 157 goats using REML method with repeatability, multi-traits Animal Test-Day Model. No associations were found with dairy traits—milk yield and content of the major milk components (fat, protein, and lactose). Also, no effect was shown of the GHR genotype on the somatic cell count (SCC).