Abstract

The modern dairy cattle breeding strategy in the Mexican tropic is to identify genes or allelic variants that can be incorporated into selection programs such as the prolactin gene (PRL) which is associated with milk production and quality. The aim of this study is to screen an American Swiss population in Chiapas, Mexico, in order to analyze the polymorphism of the prolactin gene as well as its relationship with milk production in blood samples of 417 American Swiss cattle. The genotypes were determined through the polymerase chain reaction-restriction fragments length polymorphism (PCR-RFLP) technique, using RsaI restriction endonuclease, showing a 156 bp fragment located in exon 3. Allele frequencies in the studied breed were: A = 0.8765 and B = 0.1235. The genotype frequencies of AA, AB and BB were 0.776, 0.174 and 0.026, respectively. The Chi-square indicated that genotype distributions were not in the Hardy-Weinberg equilibrium (P<0.05). The results show that animals with genotype AA had a greater milk production during lactation than genotypes AB and BB (P<0.05), with genotype BB being the one that had the lowest production (P<0.05). It was concluded that the identification of the prolactin polymorphism in this population will allow the achievement of a better efficiency in the selection of breeding animals.

Key words: Brown Swiss, prolactin, polymorphism, milk, RFLP-RsaI.