Method: Research work was carried out on 50 Sahiwal and 50 HF Crossbred cattle in the department of Animal Genetics and Breeding College of Veterinary Science & A.H. Jabalpur. During the research work the PCR amplified products of 121bp was digested by restriction endonuclease enzyme DdeI, which recognizes G^AATTC sites.

Result: The patterns showed that the presence of one restriction site on one alleles and absence of restriction site on other alleles resulted in the appearance of three bands of 121, 86 and 35bp. The name of above genotypic pattern was referred to as A1A2. In another case both strand had no restriction sites for the enzyme, so only one band of 121bp was observed on the gel and such genotype was designated as A2A2 type. So in β- casein gene both A2A2 and A1A2 genotypes were observed in Sahiwal and HF crossbred cattle. The genotypic frequencies of β-casein (CSN2) gene for A1A1, A1A2 and A2A2 are 0.00, 0.30 and 0.70 in Sahiwal and 0.00, 0.64 and 0.36 in HF crossbred cattle, respectively and the gene frequency A1 and A2 is 0.15 and 0.85 in Sahiwal and 0.32 and 0.68 in HF crossbred cattle. High frequency of A2 allele was observed in both the breeds of cattle under the study. Association studies with lactation length revealed that significantly higher LL was noticed in A2A2 genotype of HF crossbred among both breeds of cattle’s. The higher LL was also noticed in A2A2 genotyped animals as compared to A1A2 genotyped animals of Sahiwal and HF crossbred cattle.