Modern dairy cattle breeding strategies depend on linkage analysis and quantitative trait loci (QTL) of genes involved in milk yield and composition. This is because of their biological desired quantitative traits that play key roles in milk production. In this study, three genes directly related to milk production: prolactin (PRL), bovine kappa-casein (K-CN) and the pituitary-speciﬁc transcription factor (PIT-1) were analyzed in 144 cows. The aim of this study was to identify polymorphisms in the Holstein-Friesian cattle breed in Palestine in relation to the genetic markers and allelic variants of the three genes. Collection of samples depended on an experimental design that was completely randomized (CRD) and blood samples were collected from different cities across the West Bank, Palestine. The genotypes were determined through the polymerase chain reaction-restriction fragments length polymorphism (PCR-RFLP) technique. The amplified fragments of PRL (294-bp), K-CN (530-bp) and PIT-1 (451-bp) were digested with RsaI, HindIII and HinfI, respectively. Statistical analysis found that the prolactin allelic substitution (AG, GG) played a role in milk production with a p-value of 0.00643 and α (0.001**), the AG allele of PRL being more favorable for milk production as compared to the GG allele. Genetic variants of the bovine K-CN gene played a role in milk production with a p-value of 0.04071 and α (0.01*), the AA allele possessing more positive effect than the BB and AB alleles. Similarly, the allelic substitution of the PIT-1 gene affected milk production with a p-value of 2.274e-05 and α (0***), the AA allele exercising a more positive effect followed by the AB and BB alleles, respectively. Among the three studied breeds (Friesian, hybrid and local), results show that the Friesian breed possesses higher overall milk production in Palestine as compared to the other two breeds.
Key words: Prolactin (PRL), bovine kappa-casein (K-CN), pituitary-speciﬁc transcription factor (PIT-1), polymerase chain reaction-restriction fragments length polymorphism (PCR-RFLP).
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