Milk production in high-yielding dairy cows under different environment temperatures

The aim of this paper was to evaluate the effects of different environment temperatures on milk production in dairy cows under conditions typical for the moderate-continental climate. The trial was carried out on 40 Holstein Friesian dairy cows (20 cows in summer and 20 cows in the spring season). The cows were monitored from day 30 to day 90 of lactation and housed in a stable which during the summer was not equipped with additional cooling. The temperature-humidity index (THI) was recorded hourly. Milking was measured daily. Based on the results calculated for average all-day THI, during the spring season the cows were not exposed to heat stress. During the summer season, especially in the afternoon hours, the cows were exposed to the effects of moderate to severe heat stress. Average daily milk yield in the spring season from day 30 to day 90 of lactation was significantly higher (p < 0.001) compared to the same lactation period during the summer season. Nevertheless, there was no significant difference in average milk yield from day 30 to day 60 of lactation (p = 0.110) between spring and summer season. Average milk yield per cow from day 61 to day 90 of lactation in the summer period was significantly lower (p < 0.001) compared to the same period during the spring season. Average daily feed consumption was significantly lower (p < 0.001) during the summer compared to spring during whole trial period. In conclusion, although feed consumption was significantly lower during the summer season throught the study, milk production compared to the spring season, was significantly lower only from day 61 to 90 of lactation. This could mean that the negative impact of feed intake on milk production is not as effective during early lactation (until day 60 of lactation), when homeorhetic mechanisms play a significant role in the rearrangement of metabolism, as it is thereafter i.e. from day 61 to 90 of lactation.