Study on Kappa-casein (k-CN) gene polymorphism in Achai, Sahiwal cow and Nili-Ravi buffalo breeds

In the present study Kappa-casein (k-CN) gene polymorphism was studied in two different Pakistani cattle (Achai and Sahiwal) and one buffalo (Nili-Ravi) breeds. Blood samples were collected from randomly selected animals (100 samples each of Achai, Sahiwal and Nili-Ravi). The genomic DNA was extracted using standard protocol. The extracted DNA was then amplified for 443 bp k-CN gene fragment (Exon IV) using optimized set of primers. The amplified PCR products were subjected to restriction digestion by PCR-RFLP using HindIII restriction endonuclease enzyme. After incubation for about 16 hours at 37 degree C, the resulted products were analyzed on 2.5 percent agarose gel. The Achai and Sahiwal cattle were found to be polymorphic. In Achai animals the frequencies of genotypes AA, AB and BB were counted to be 0.70, 0.18 and 0.12 respectively, while in animals of Sahiwal breed these were 0.92, 0.08 and 0.00 respectively. On the other hand Nili-Ravi buffaloes were found to be monomorphic for k-CN gene as only BB genotype was detected. The allelic frequency of allele A in Achai cattle was 0.79, in Sahiwal was 0.96 and in Nili-Ravi was 0, while that of allele B was 0.21, 0.04 and 1.00 respectively. The chi-square test for three animal breeds used in the present study showed that the Sahiwal and Nili-Ravi animal populations were in Hardy-Weinberg equilibrium (HWE), while Achai was not in HWE. It was concluded that AA genotype and allele A occur at high frequency in Achai and Sahiwal cattle while in Nili-Ravi buffaloes BB genotype and allele B were present at high frequency. As k-CN variant B is best for milk quantity and quality, therefore it was concluded that BB genotype animals are best for further selection and designing breeding strategies to enhance milk yield and subsequent cheese production.