Milk production and genotypic variants for Prolactin (PRL) and Prolactin receptor (PRLR) Slick1 genes identified using polymerase chain reaction-restriction fragment length polymorphism on selected dairy cattle farms in the Philippines

Importance of the work: A locally developed polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) test for the Prolactin (PRL) and Prolactin receptor (PRLR) Slick1 gene variants is the first to be made available to dairy farms that is comparable to commercial genotyping kits. Objectives: To test the locally developed PCR-RFLP assay for determining the genotype frequencies of the PRLR Slick1 variant and PRL genes and to determine whether there are variations in milk production performance of cows according to genotype. Materials and Methods: Genomic DNA samples of 479 dairy cattle from four farms in the Philippines were genotyped using PCR-RFLP with PciI and RsaI restriction enzymes for the PRLR Slick1 and PRL genes, respectively. Genotype and allele frequencies were determined and the 305 d lactation period (305D) milk yield of cows was analyzed according to genotype. Results: The PCR-RFLP of the PRL gene identified three genotypes: AA, AG and GG, with allele frequencies of 0.16 (A) and 0.84 (G). The PCR-RFLP of the PRLR Slick1 gene variant had two genotypes: hetero-slick (CT) and non-slick (CC), with allele frequencies of 0.94 (C) and 0.06 (T). The genotypes obtained using the PCR-RFLP assay were consistent with the commercial genotyping method. The main effect of PRL was associated with significantly higher 305D milk yield for GG genotyped cows. There were no significant differences in the 305D milk yield among the cows with different PRLR Slick1 genotypes. The interaction of calving season × PRL genotype produced a significantly lower 305D milk yield for the GG cows calving during the hot-humid season, whereas no significant difference was observed for the AG cows calving regardless of season. However, while the results are preliminary, irrespective of the PRL genotype, hetero-slick cows fared better than non-slick cows calving during the hot-humid season. Main finding: The results from the locally developed PCR-RFLP test for PRL and PRLR Slick1 mutation were comparable to those from the commercial genotyping method, which should enable local testing for selection and planned breeding of animals carrying the favorable alleles of the PRL and PRLR Slick1 genes.