Effect of Calving Season on Productive Performance of Dairy Cows

Simple Summary In the last decade, we have been witnessing serious climate changes related to global warming. This affects all living beings, including dairy cows. As the climate warms, dairy cows in temperate climate zones experience heat stress (HS), which affects the quantity and quality of milk they produce. In the present scientific work, the influence of the calving season on the yield and composition of cows' milk was studied. As a result of the study, it was found that cows that calved in summer, under conditions of HS, had the lowest milk yields for lactation, the lowest milk yields at the peak of lactation, and the lowest fat content compared to cows that calved in other seasons of the year. Regarding the protein content of the milk, a tendency was found for cattle that calved in the summer to have the highest values of this trait.Abstract The aim of the present research was to study the influence of the calving season in conditions of the upcoming climate changes on the productive traits of dairy cows in Bulgaria. The study was conducted on a cattle farm with a capacity of 500 dairy cows, which were loose-housed in open free-stall barns (shed-type). In the research, 286 lactations of 199 Holstein cattle from the studied farm were included. The cows with the highest average milk yield for lactation-8522.2 kg-calved in the spring, while the cows with the lowest milk yield-8082.7 kg-calved in the summer. Cows that calved in the spring had the highest maximum daily milk yield (lactation peak)-38 kg-whereas cows that calved in the summer had the lowest-35.7 kg. Regarding the composition indicators of milk, fat, and protein content, no significant effect of the calving season was found, but there was a tendency for the lowest values for the percentage of fat in milk to be reported for cows that calved in the summer-3.68%-and the highest for those calved in the spring-3.71%. Regarding the percentage of protein in the milk, the lowest values were observed for cows that calved in autumn-3.19%-and the highest for cows that calved in summer-3.27%.