Metabolic disorders as a factor influencing morphological and productive parameters in Holstein cows

The aim of the study was to establish the relationship between polymorbid pathology, morphological changes in the liver, and the productivity of animals at different lactations. A complex of clinical, morphological, histological, and cytometric methods was applied. A comparative analysis was conducted between the control and experimental groups of cows in their first, second, and third lactations. A total of 327 animals were examined, among which pathological conditions were detected in 60% of first-lactation cows, 53.57% of second-lactation cows, and 47.27% of third-lactation cows. For the morphological study, animals with combined metabolic disorders were selected, namely ketosis in combination with endometritis, mastitis, or hypocalcaemia. It was found that the proportion of such combinations was 20.95%, 17.85%, and 14.54% in the first, second, and third lactations, respectively. The average daily milk yield in the experimental groups was lower than in the control groups, while body weight significantly (p < 0.05) decreased across all age groups. The experimental animals showed an increase in both absolute and relative liver mass (p < 0.001), indicating functional hypertrophy of the organ. Histological examination revealed disruption of lobular architecture, diffuse vacuolisation of hepatocytes, areas of necrosis, infiltration of portal tracts, and the development of periportal fibrosis. In cows with a combination of ketosis and mastitis, signs of chronic hepatitis were observed, whereas in those with ketosis and hypocalcaemia, hepatosis with macrovesicular steatosis predominated. Cytometric analysis demonstrated a significant increase in the volume of hepatocytes and their nuclei (p < 0.05; p < 0.01) along with a decrease in the nuclear-to-cytoplasmic ratio, confirming the development of fatty degeneration. The degree of morphological alterations intensified with age and the duration of the lactation period. The practical value of the study lay in establishing morphological and cytometric criteria of liver lesions under polymorbid conditions, which could be applied to diagnose the level of metabolic load, predict disease progression, and develop preventive measures in animal husbandry