Beta-casein gene polymorphism in Serbian Holstein-Friesian cows and its relationship with milk production traits

The most common types of beta-casein in cow’s milk are A1 and A2, which differ in one amino acid. During the gastrointestinal proteolysis of A1 beta-casein in humans this difference results in the release of beta-casomorphin-7, an opioid which may lead to severe effects on human health, causing various ailments (type-1 diabetes mellitus, ischemic heart disease, arteriosclerosis, sudden infant death syndrome, autism, schizophrenia, gastrointestinal digestive discomfort, as well as increased gastrointestinal transit time). By contrast, A2 beta-casein cannot exert these effects owing to its different composition and metabolism. Furthermore, studies have shown that it can influence milk productivity traits. Our research aimed to screen the frequency of A1 and A2 alleles of beta-casein gene in a population of Serbian Holstein-Friesian cows and to detect how the genotypes influence milk production, and milk protein and fat yields. Out of 106 animals, 13 (12.26%) were of A1A1 genotype, 58 (54.72%) of A1A2, and 35 (33.02%) of A2A2 genotype. Milk yield was significantly (P<0.01) higher in A2A2 compared to both A1A1 and A1A2 genotypes. Milk protein concentrations were significantly (P<0.01) higher in A2A2 compared to A1A2 genotype, while milk fat concentrations were significantly (P<0.01) higher in A2A2 compared to both A1A1 and A1A2 genotypes.
Najzastupljeniji tipovi beta kazeina u kravljem mleku su A1 i A2 koji se razlikuju u jednoj aminokiselini. Tokom gastrointestinalne proteolize A1 beta kazeina kod ljudi, oslobađa se betakazomorfin 7, opioidni peptid koji može uzrokovati pojavu raznih oboljenja (dijabetes melitus tip 1, ishemijska bolest srca, ateroskleroza, sindrom iznenadne smrti odojčadi, autizam, šizofrenija, nelagodnost u digestivnom sistemu, kao i produženo vreme gastrointestinalne pasaže). Suprotno tome, A2 beta kazein, zbog svog sastava i drugačijeg metabolizma, ne može da ispolji navedene efekte. Istraživanja su pokazala takođe, da može imati uticaj na proizvodnju i sastav mleka. Ovo istraživanje imalo je za cilj da ispita frekvenciju beta kazeinskih genskih alela A1 i A2 u populaciji holštajnfrizijske rase u Srbiji i da utvrdi kako genotipovi utiču na proizvodnju mleka, mlečnih proteina i masti. Od 106 ispitanih životinja, kod 13 (12,26%) je ustanovljen genotip A1A1, kod 58 (54,72%) A1A2, a kod 35 (33,02%) A2A2 genotip. Proizvodnja mleka bila je značajno veća kod životinja sa A2A2 genotipom u poređenju sa genotipovima A1A1 i A1A2 (P<0,01). Koncentracije proteina u mleku bile su značajno veće kod životinja sa A2A2 genotipom u poređenju sa životinjama A1A2 genotipa (P<0,01), dok su koncentracije mlečne masti bile značajno veće kod životinja A2A2 genotip u poređenju sa životinjama A1A1 i A1A2 genotipa (P<0,01).