Milk protein genes are the preferred DNA-markers which stipulate quantitative and qualitative levels of milk performance of cattle. The structure genes – kappa-casein, beta-lactoglobulin and alfa-lactalbumin – are characterized by special impact on milk productivity and technological properties of milk.

α-Lactalbumin (α-LA) is a metallic protein, major whey protein of bovine milk. Its part in whole milk protein is 2–5 %. The main biologic role of α-LA is the involving in the synthesis of lactose.

α-LA polymorphism regarding to indices of milk productivity was studied for many cattle breeds. Particularly, Bleck and Bermel (2009) revealed that allele A of α-LA in Holstein cattle associated with higher milk, fat and protein yield. At the same time allele B associated with higher fat and protein content.

The objective of this work was to study the possibilities of α-LA polymorphism using for assessment of milk productivity potential in Ukrainian Black-and-White breed.

We took into account the main indices of milk productivity in 200 Ukrainian Black-and-White cows tested on α-LA polymorphism.

Milk yield was calculated based on the results of monthly control milking. Fat and protein content in milk was measured by means of device «Ekomilk KAM-98.2». Total solids content was determined by method of drying to constant weight, milk solids non-fat (MSNF) content and lactose content – by using milk analyzer AM-2, casein content – by formol method. The casein number was calculated as the ratio of casein to whole protein. Milk density was measured using a lactodensimeter.

The rennetability of milk was ascertained by the trial of rennetability. 20 cm³ of milk was heated up to 35 ºC in water bath, 1 cm³ of rennet powder with the strength of 1:400 was added, milk was stirred. The time till the creation of first curd flakes was measured.

Heat stability (alcohol number) was determined by the titration with 96 % ethanol.

Statistical analysis was carried out in program Statistica 6.0.

In the examined herd of dairy cows, two alleles of the α-LA gene (α-LA A and α-LA B) and three genotypes (АА, АВ та ВВ) were identified. The conducted research showed that 45 % of the population had the AB genotype, 36,5 % had the AA genotype and 18 % had the BB genotype. This has been confirmed by the results obtained for different populations of Black-and-White cattle.

The highest milk yield (5615 kg) was received from cows with genotype α-LA ВВ. It was 243 (p<0,05) and 107 (p<0,05) kg higher than milk productivity of cows-carriers of AA and BB genotypes respectively. These results are in agreement with data obtained for Russian Black-and-White breed.

Significant differences between the cows of different α-LA genotypes were not found for the content of main substances of milk. Animals with heterozygote genotype had slightly higher indices of fat, protein, total solids and lactose content in comparison with homozygotes, but the statistically significant differences were revealed only on protein content – АB>AA, 0,04 %, p<0,05; AB>BB, 0,08 %, p<0,05.

We determined the highest casein content in cows with genotype α-LA ВВ. The casein number of this milk was 78,8 %, that copulate its best rennetability (28,4 min). Such characteristics are desirable for cheese making. At the same time the highest heat stability was in milk from cows with genotype α-LA AA, alcohol number of this milk was 59,4 % of ethanol.

Results of disperse analysis showed the absence of significant associative relationships between milk performance traits and polymorphism of α-LA gene except for milk and protein yield where we observed the significant dependence. The force of impact (η²) of genotype on milk yield was 1,4 % (p=0,037), protein content – 2,5 % (p=0,041). The direction of this connection indicates that allele α-LA A is desired in case of animal selection on protein content.

The results presented here prove the feasibility of using the α-LA gene polymorphism for assessment of milk productivity potential in Ukrainian Black-and-White dairy cattle.

Key words: milk productivity, alfa-lactalbumin gene, PCR-RFLP, genotypes, milk yield, milk content, cheese-making properties, heat stability.