Study of influence of heat stress on some physiological and productive traits in Holstein-Friesian dairy cows
¹Trakia University, Faculty of Agriculture, Department of Applied Ecology and Animal Hygiene, BG6000 Stara Zagora, Bulgaria
²Trakia University, Faculty of Agriculture, Department of Animal Husbandry – Ruminants and Dairy Farming, BG6000 Stara Zagora, Bulgaria
³Institute of Agriculture, BG6000 Stara Zagora, Bulgaria
The aim of the research was to study the effect of heat stress (HS) on some physiological and productive traits in Holstein-Friesian dairy cows. The study included 22 cows on different parities. In the building where the cows were housed, the temperature-humidity index (THI) was reported at 10:00 and 15:00 h, at the same time the rectal temperature (RT) and respiratory rate (RR) were reported for each of the examined cows. The daily rumen activity was taken from the SCR system by Allflex. The average THI values in May were 71, in June – 75, in July – 74, and in August – 77, from which it follows that in the summer months the cows were in conditions of mild to moderate heat stress throughout the day. The average daily milk yield of the cows increased from May to June and reached 41.44 kg day-1, then decreased in July and August to 37.2 and 32.48 kg day-1, respectively. With an increase in the THI values, an increase in the RR and RT was registered, as in THI above 79 the RR was 56.54 per min, and the RT was 39.33 °C. With increasing the THI values, the rumination of the cows decreased from 563 per day at THI < 72 to 542.5 at THI > 79. In cows with high daily milk yield, a higher RT was registered, and in cows with more than 50 kg per day, the RT was 39.09 °С. A more intense rumination was found in cows with higher daily milk yield. In cows with an average daily milk yield of 33.26 kg, an average of 450 ruminations per day were reported, and in those with an average milk yield of up to 42.89 kg – 650 ruminations per day. From the research conducted it was found that the studied physiological traits – rectal temperature, respiration rate and rumination are influenced by HS and the intensity of this effect depend on the daily milk yield of cows and THI levels.