# Association of β-casein gene polymorphism with milk production characteristics in Holstein cows

## TL;DR

This study found no significant link between β-casein gene variants and milk production traits in Holstein cows.

## Contribution

It is the first to investigate β-casein gene polymorphism's effect on milk production and metabolites in Brazilian Holstein cows.

## Key findings

- No association was found between β-casein gene polymorphism and milk production or composition traits.
- A2A2 genotype showed higher glucose levels compared to A1A1 and A1A2 genotypes.
- Polymorphism of A1 and A2 alleles does not alter milk composition or metabolites.

## Abstract

Summary: Information on milk production and composition was obtained from 1,786 lactating cows in a Brazilian commercial herd, for which data provided by the dairy farm in Brazil were adopted as selection criteria, such as genotypes for the β-casein gene extracted from the Clarifide Zoetis software, days in milk, and number of lactations. Thus, 18 cows were selected, analyzing the association between the genotype for the β-casein CSN2 gene and milk production and composition characteristics and energy, enzymatic, and nitrogen metabolites of blood, milk, and urine. No association between β-casein gene polymorphism and any of the variables under study was observed.

Summary: Information on milk production and composition was obtained from 1,786 lactating cows in a Brazilian commercial herd, for which data provided by the dairy farm in Brazil were adopted as selection criteria, such as genotypes for the β-casein gene extracted from the Clarifide Zoetis software, days in milk, and number of lactations. Thus, 18 cows were selected, analyzing the association between the genotype for the β-casein CSN2 gene and milk production and composition characteristics and energy, enzymatic, and nitrogen metabolites of blood, milk, and urine. No association between β-casein gene polymorphism and any of the variables under study was observed.

•Information on cows from a dairy farm in Brazil was selected for the β-casein gene.•No association was observed between β-casein gene polymorphism and milk production and composition.•Polymorphism of A1 and A2 alleles does not alter milk composition and metabolites.

Information on cows from a dairy farm in Brazil was selected for the β-casein gene.

No association was observed between β-casein gene polymorphism and milk production and composition.

Polymorphism of A1 and A2 alleles does not alter milk composition and metabolites.

The aim of this study was to analyze the association between the β-CN CSN2 gene polymorphism, energy, enzymatic, and nitrogenous metabolites, and production, composition (fat, protein, lactose, total solids, nonfat solids), and SCC in the milk of Holstein cows submitted to the same nutritional and environmental conditions. Eighteen cows (6 A1A1 genotype, 6 A1A2 genotype, and 6 A2A2 genotype) were selected and matched for parity, calving season, and days in lactation. For the statistical analysis, a fixed linear model was applied in which genotypes were considered as a fixed effect and the dependent variables included metabolites, milk production, milk composition, and SCC. We found no statistically significant differences associating the genotype for the β-CN CSN2 gene with milk production and composition characteristics or with energy, enzymatic, and nitrogen metabolites of blood and milk, except for variable glucose concentration (mg/dL), in which only the A2A2 genotype presented the highest means (67.78a) in relation to the other genotypes A1A1 (58.28b) and A1A2 (55.69b), where the letter a corresponds to the value of the highest mean and the letter b corresponds to the value of the lowest mean. Under the conditions in which the experiment was developed, the highest averages were numerically observed for variables milk production (kg/d), milk composition and yield (%), and urea nitrogen concentration (%) in the blood, milk, and urine of cows carrying the heterozygous genotype (A1A2) compared with both homozygous genotypes (A1A1 and A2A2), and we found that polymorphism of A1 and A2 alleles does not alter milk composition or blood and urinary metabolites.