Genetic Variability in the Growth Hormone Gene (A781G) and Its Association with Milk Yield Performance in Crossbred Anglo-Nubian Dairy Goats

Abstract

This study was conducted to evaluate the genetic variation in the growth hormone (GH) gene and the influence of GH polymorphisms on the milk yield in crossbred Anglo-Nubian goats (n = 101) from three selected dairy farms in the Philippines. The first two farms were located in Barangay Awang, Opol, Misamis Oriental, while the third farm was situated in Barangay Talay, Dumaguete City, Negros Oriental. Milk production data from the first to ≥ fourth parity was standardized to a 90-d and 140-d milking period. Genomic DNA was isolated from hair follicles and the A781G region of the caprine GH gene was amplified. Genotyping was performed via polymerase chain reaction – restriction fragment length polymorphism (PCR-RFLP) using the HaeIII restriction enzyme (RE). Genotypic frequencies of 0.76 for AB and 0.24 for AA and allelic frequencies of 0.62 for A and 0.38 for B were recorded. In order to determine the effect of genotypes to milk yield, a two-way factorial (2 x 4) in randomized complete block design (RCBD) was performed. GH genotypes (AA, AB) and goat parities (first to ≥ fourth lactation) were considered as the main factors, while the three farms were used as the blocking factor. Milk yield traits between GH genotypes were insignificant (p > 0.05). However, dairy goats with AB genotype consistently produced higher milk yield than those with AA. Future studies should be conducted in other goat breeds to further expound the effects of GH polymorphism on economically important traits in addition to milk yield.