Abstract:
The objective of this study was to estimate effects of beta and kappa casein as candidate genes on milk yield, protein yield and protein percentage of 87 crossbred dairy cattle with production records. The investigation on beta and kappa casein genotypes were by allele-specific polymerase chain reaction (ASPCR) and polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP), respectively. Alleles of beta casein were A[superscript 1] A[superscript 2] and B with allele frequencies of 0.30, 0.61 and 0.09, respectively. Beta casein genotypes were A[superscript 1]A[superscript 1] A[superscript 1]A[superscript 2] A[superscript 2]A[superscript 2] A[superscript 2]B and A[superscript 1]B or BB with genotype frequencies of 0.06, 0.41, 0.36, 0.11 and 0.06, respectively. Alleles of kappa casein were A B and E with allele frequencies of 0.72, 0.26 and 0.02, respectively. Kappa casein genotypes were AA AB AE BB and BE with genotype frequencies of 0.50, 0.40, 0.03, 0.06 and 0.01, respectively. Effects of beta and kappa casein genotypes on milk production records were investigated using animal models. Single gene analyses by model1a-b for beta and kappa casein genotype showed that cows with A[superscript 1]A[superscript 1] and A[superscript 1]A[superscript 2] beta casein genotypes produced highest milk and protein yield. Milk and protein production were highest for the kappa casein AA genotype, and protein percentage was highest for the EE genotype. Multigene analyses by model2 showed that A[superscript 1]A[superscript 1]-AB, A[superscript 1]A[superscript 2]-AA and A[superscript 1]A[superscript 1]-AA genotypes were associated with the highest milk and protein production, and A[superscript 1]A[superscript 2]-AE genotype was associated with the highest protein percentage. These observations implied that the interaction between the beta and kappa casein loci may be the important factors affecting milk production. A small set of cow data on milk production made this study results inconclusive. Further studies should be conducted in an experimental data to identify the real effects of particular genotypes.