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In the present study, polymorphism of PRL gene at exon-3 and its association with milk production traits inFrieswal cattle was investigated. Prolactin (PRL) gene exerts multiple effects on the mammary gland include mammogenesis, lactogenesis and galactopoiesis. In order to evaluate the PRL gene polymorphism, the restriction fragment length polymorphism (RFLP) method was employed in this research. Blood samples were collected from randomly chosen 54 Frieswal lactating cows. Genomic DNA was extracted from venous blood by the method of John et al (1991) with slight modification and amplified by polymerase chain reaction technique. The PRL gene of the Frieswal cattle was amplified to generate a 156 bp fragment. The PCR products were electrophoresed on 2% agarose gel and stained by ethidium bromide. Then they were digested of amplicons with Rsa I, which revealed two alleles A and B. Data were analyzed by using Pop GenePopgene32 software package and association was analyzed by simple analysis of variance model. In this population, AA, AB, and BB genotypes were identified with 0.315, 0.629 and 0.056 frequencies, respectively. Allele frequencies of A and B were 0.630 and 0.370, respectively. The significant (P<0.05) chi-square value in Frieswal cattle breeds showed that the studied population was not in Hardy-Weinberg equilibrium. It is concluded from the results of present study that the animals of BB genotype for higher lactation length and AB genotype for lactation yield and animals of AA genotype for minimum service period may be selected for future breeding.

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Background: Polymorphisms in candidate beta-lactoglobulin genes are associated with traits of economic importance in cows and are related to milk composition, quality, production as well as cheese-production. The objective of the study was to evaluate the effects of breed, season and polymorphism on milk quality and yield in Jersey and Crossbred Holstein Friesian cows. Methods: The quality traits studied were fat %, lactose %, protein %, SNF, density and ash while quantity traits were average monthly milk yield, protein yield and fat yield. The beta-lactoglobulin gene exon IV (262 bp) was screened for polymorphisms by PCR-RFLP using BsuRI (Hae III) enzyme. Result: Our investigation revealed only two patterns AA and AB in both the breeds under study. BB genotype was absent. AA genotype was most abundant in Jersey cows (0.68) and crossbred HF cows (0.56). A allele frequency was highest in Crossbred HF cows (0.72) and Jersey cows (0.66). In Jersey genotype AB was observed to be responsible for high milk yield, protein and fat yield in each season whereas it was genotype AA of crossbred HF cows affecting milk yield, protein and fat yield. In crossbred HF cow, genotype effect was observed to be non-significant (p greater than 0.05) on all quality traits and effect of season was significant on lactose % and fat %. In Jersey cows, genotype and season effects were significant (P less than 0.05) on fat % concluding that the breed, season and genotype affectmilk quality and yield.

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