Milk yield, composition and cholesterol level in dairy cows fed rations supplemented with zinc and fatty acid calcium salts

Abstract

In an experiment conducted on 16 Red-and-White cows in a 2 × 2 Latin square design, the effect of two levels of zinc and calcium fatty acid salts on milk yield, composition and cholesterol level were studied. Cows were a fed diet consisting of maize and grass silage, ground barley, wheat bran and rapeseed meal with mineral mixtures, which in the control groups had a low level of Zn and fatty acid salts but in the experimental groups was supplemented with 6% (DM basis) calcium fatty acid salts and mineral mixture enriched with 6 g Zn/kg that corresponds to 480 mg Zn/cow/day. Intake of DM was 19.2 ± 0.28 kg/d, in this 12.1 ± 0.22 kg was from silages and 7.1 ± 0.16 from concentrate. Mean milk yield did not differ significantly between the treatments and was 26.2 ± 0.68 kg/day; cows on the diet with the higher level of Zn produced 0.9 kg/day less, those receiving fatty acid salts gave about 0.93 kg/d more milk, but the differences did not reach statistical significance. Milk from cows fed the diet supplemented with 6% fatty acid salts contained less fat and protein (P<0.05) but had a higher acidity (P<0.01) and renneting time (P<0.05). Enrichment of the diet with Zn did not significantly affect the content of the nitrogen fraction including casein. Addition of fatty acid salts to the diet resulted in a significant decrease of total-N, protein-N, casein-N fractions (P<0.01) and saturated fatty acids (P<0.05) but increased the unsaturated fatty acid (P<0.05) level in milk. The higher Zn level fed with the diet elevated its content in the blood (P<0.01), whereas the level of other determined metabolites did not differ significantly between treatments. Feeding cows CaFA salts significantly elevated triglyceride, total cholesterol, HDL (P<0.01), alkaline phosphatase and magnesium levels (P>0.05) in blood plasma. Feeding cows with diets supplemented with Zn or CaFA salts did not change milk total cholesterol levels, with the mean concentration in milk being 17.2 ± 0.4 mg/100 ml.