Effects of different dietary cobalt levels on milk productivity and milk composition in lactating dairy cows

The study aimed to evaluate the effect of different cobalt levels in the diets of lactating dairy cows on milk productivity and milk composition. The experiment was conducted on Simmental cows at STOV Agrospilka. Three groups of cows (12 animals per group) were formed according to the principle of analogs. The control group received a basal total mixed ration containing 0.2 mg Co/kg of dietary dry matter (DM), whereas the experimental groups received cobalt concentrations of 0.5 and 0.8 mg/kg DM, respectively. The experimental period lasted 90 days. Milk productivity was evaluated monthly through individual control milkings. Milk samples were analyzed for fat, protein, and dry matter content using standard laboratory methods. Statistical analysis was performed using one-way ANOVA followed by Tukey–Kramer multiple comparison test, while data normality was assessed using the Shapiro–Wilk test. The results demonstrated that increasing dietary cobalt levels positively affected milk productivity. Over the 90-day experimental period, the average daily milk yield in cows receiving 0.5 and 0.8 mg Co/kg DM was 34.22 and 34.63 kg, respectively, compared with 32.68 kg in the control group. The greatest effect was observed during the peak lactation period, when the difference between the experimental and control groups reached 5.1–6.3 % (P < 0.05). Gross milk yield also increased significantly in the experimental groups, exceeding the control by 4.7–6.0 % over the entire trial period. The medium cobalt level (0.5 mg/kg DM) had the most pronounced positive effect on milk composition. Milk fat content increased to 3.92 % compared to 3.80 % in the control group (P < 0.05), while milk protein content reached 3.24 % versus 3.13 % in the control (+3.5 %; P < 0.05). Milk dry matter content also increased to 12.54 %, exceeding the control value of 12.25 % (+2.4%; P < 0.05). Increasing cobalt supplementation to 0.8 mg/kg DM did not further improve these parameters, indicating a physiological saturation effect. The obtained results indicate that cobalt supplementation at the level of 0.5 mg/kg DM optimizes ruminal vitamin B12 synthesis, improves nutrient utilization efficiency, and enhances milk productivity and milk quality in high-producing dairy cows. At the same time, further increases in cobalt concentration above this level appear biologically and economically unjustified.