Background and Aim: The market demand for the quality of milk and dairy products, in particular in terms of such indicators as fat content, the amount and composition of milk protein, etc., is growing. Thus, the need for the selection of dairy herds using genetic markers associated with qualitative traits of milk productivity is becoming urgent. This study aimed to determine the preferred and undesirable genotypes of the AluI polymorphism of the growth hormone gene and SnaBI polymorphism of the insulin-like growth factor-1 gene associated with milk productivity and quality indicators of the black-and-white breed. The genotypes of animals were determined by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP).

Materials and Methods: Samples of the black-and-white breed from Kazakhstan served as the research subjects. The polymorphism of the growth hormone and insulin-like growth factor-1 genes was determined by PCR-RFLP. The relationship of bGH-AluI and bIGF-1-SnaBI polymorphisms with productivity was assessed (fat, protein, and milk yield for 305 days of lactation, live weight, somatic cells, and milk production coefficient) by analysis of variance using Statistica 6.0 software.

Results: The black-and-white cows with the bGH-AluI^LV genotype had significantly higher milk yield in 305 days (3174.5±157.2 kg) than those with the bGH-AluI^LL (2940.0±152.6 kg) and bGH-AluI^VV genotypes (2964.0±36.0; p<0.05). The milk fat content of cows with genotypes bGH-AluI^LV and bGH-AluI^LL (121.8±6.5 and 120.6±10.2, respectively) was significantly higher than those with bGH-AluI^VV genotype (109.8±10.8; p<0.05). The black-and-white cows with the bGH-AluI^LV genotype (96.7±5.3) had significantly more milk protein than those with the bGH-AluI^LL (90.3±5.6) and bGH-AluIVV (86.9±4.6) genotypes (p<0.05). There were no statistically significant differences in the indicators of milk productivity of cows with different genotypes of bIGF-1-SnaBI polymorphism.

Conclusion: The results showed that the bGH-AluI^LV genotype was preferred for the black-and-white breed. The study demonstrated that genotype determined the relevant qualities, while the conditions of feeding, maintenance, and industrial technology provided the manifestation of this genotype. Thus, cows of the same (Wis Burke Ideal) line, having common ancestors in close (IV–V) ranks but living in different farming conditions, had large differences in milk productivity level. The variation was 2046 kg or 67.6% of milk per lactation.

Keywords: black and white breed, growth hormone gene, insulin-like growth factor-1 gene.