High-yielding cows are prone to negative energy balance due to high lactation and insufficient dry matter intake after calving. This leads to the mobilization of fat and protein in the body to meet the nutrient needs of the lactating cow. High levels of nonesterified fatty acids are maintained by fat and protein mobilization, leading to ketosis due to incomplete oxidation of ketone bodies. The purpose of the research was to investigate the effect of probiotics on the productivity of cows and the quality of milk in ketosis. Research was conducted in the period from October to November 2021 on Holstein cows in the limited liability company "Lan" Agricultural Company of the North-Eastern region of Ukraine. It was found that in cows in the post-calving group, seven days after calving, the level of ketone bodies in the blood of the cows ranged from 1.0 to 2.1 mmol/l, which is higher than in the control by 71.42–185.71%. Two weeks after probiotic administration, ketone levels were between 0.5 and 1.2 mmol/L, 16.65–100% higher than controls. On the 28th day of the study, the content of ketone bodies in cows was within the physiological norm. In cows suffering from ketosis, productivity was reduced on the seventh day of research by 22.42–336.4%, on the 14th day by 11.6–29.35%. During the study of productivity, its restoration to the indicators of healthy animals on the 28th day after calving was established at the level of 28-29 kg/day. At the same time, the content of microorganisms and somatic cells had a direct correlation with productivity, and on the 28th day, the milk of all experimental cows was suitable for consumption and corresponded to the "extra" variety.
In the first week after calving, the ratio of milk fat and protein in the milk of cows with ketosis was slightly imbalanced, which is a sign of ketosis. On the seventh day of the study, the milk fat level exceeded the protein content in cow 6905 by 32%, in cow 6852 by 39.25%, in cow 6916 by 30.34%, in cow 7642 by 41.17%, in cow 6187 – by 33.62%, in cow 2563 – by 36.40%, in cow 3891 – by 41.63%. At the end of the study on the 28th day, the fat/protein ratio approached the reference level of 1:1 in all experimental animals.