Effect of wheat gluten and extracted, protected soybean meal addition to the diet of cows with different beta-lactoglobulin genotypes on the composition and physical properties of milk

The effect of wheat gluten or extracted soybean meal (300 g of crude protein/head/day) on milk yield, composition and its physical properties was analysed in 53 cows of Polish Holstein-Friesian breed with different milk beta-lactoglobulin (blg) genotypes (AA, AB and BB). The addition of wheat gluten to the diet of cows with the AA and AB blg genotypes caused a significant increase in crude protein (by 0.21; P ≤ 0.05, and 0.19%; P ≤ 0.01), casein (by 0.15; P ≤ 0.05, and 0.15%; P ≤ 0.01) and dry matter content (0.3 and 0.5%; P ≤ 0.05) in milk, and a significant increase in beta-casein production (0.6 g/l; P ≤ 0.05, and 0.6 g/l; P ≤ 0.01) and kappa-casein yield (0.3 g/l; P ≤ 0.05) in the case of cows with the AA genotype. Milk acidity and electrical resistance in milk were lowered. The cows with the BB blg genotype did not show any significant changes in milk composition. The supplementation of extracted soybean meal to cows with the AB and BB blg genotype led to a significant increase in milk protein (0.26% and 0.21%; P ≤ 0.01) and casein content (0.2 and 0.15%; P ≤ 0.01), beta-casein production (0.60 and 0.50 g/l; P ≤ 0.01) and to a decrease in kappa-casein content (by 0.7%; P ≤ 0.05) in cows with the BB genotype. The production of kappa-casein increased in cows with the AB genotype (by 0.2 g/l; P ≤ 0.01). In the case of all genotypes, an increase in milk active acidity and thermostability and a decrease in electrical resistance in milk were noted. It was observed that cows with different blg genotypes differently utilised the protein from given supplements for the production of individual milk components, which may be used in rationalisation of their feeding and improvement of milk content.