Brown Swiss cows are more heat resistant than Holstein cows under hot summer conditions of the continental climate of Ukraine

Finding livestock breeds that are resistant to high temperatures may be one of the strategies for mitigating the impact of global climate change on dairy farming. In this investigation, we studied the heat resistance of Holstein (HB) and Brown Swiss (BS) cows on two commercial dairy farms under the hot summer conditions of Ukraine. The physiological response of animals determined heat resistance by measuring rectal temperature (RT) and respiratory rate (RR) in the morning (from 4:00 to 6:00) in comfortable conditions and the afternoon (from 14:00 to 16:00), during heat load. The temperature-humidity index (THI) was used to characterize weather conditions and microclimate in naturally ventilated rooms (NVBs). BS cows were found to be heat resistant. The reaction of HB cows to the heat was manifested by higher growth of RT and RR, and they suffered significant losses in the daily milk yield per cow in the summer. Further research will need to elucidate the biological and genetic mechanisms of the identified breed differences in heat tolerance of dairy cows.