Effect of Growth Hormone-releasing Hormone Gene Polymorphism (GHRH/HAEIII) on First Lactation Milk Yield and Milk Composition Traits in Sahiwal Cattle

Growth hormone-releasing hormone (GHRH), also known as somatoliberin is a releasing hormone of growth hormone (GH). GHRH is a peptide hormone found mainly in the hypothalamus. The gene is significantly associated with increase milk yield in cattle. The objective of this study was to identify the polymorphism in the GHRH gene (GHRH/HaeIII) and to evaluate the relationship between the polymorphism with the breeding values for first lactation milk production and composition traits of Sahiwal cattle reared using PCR-RFLP.

A total of 130 animals were included in the study. PCR-RFLP analysis of each 297 bp PCR product was carried out using HaeIII restriction enzyme. The single trait animal model was considered for the estimation of breeding values using WOMBAT software. To study the effect of genotype on the individual trait, PROC GLM (SAS 4.3) was used.

PCR-RFLP analysis of GHRH gene revealed three genotypes with genotypic frequencies as; 0.05 (AA), 0.42 (AB) and 0.53 (BB). The allelic frequencies for A and B allele were 0.26 and 0.74, respectively. Sahiwal cows with AA genotype have significantly higher (p<0.017) fat percentage in milk while the cows with BB genotype; while the BB genotype cows characterized by significantly higher (p<0.025) first lactation 305 day milk yield. Among the three genotypes, BB was most abundant while AA genotype was rarest in the screened Sahiwal samples. The identified potential genetic marker could be used for the development of Marker Assisted Selection (MAS) strategy for higher milk yield and milk composition traits in Sahiwal cattle.