The authors studied the effect of summer heat stress from Hungary on lactating Hungarian Simmental cattle. The study was carried out in July 2019, and involved 20 multiparous lactating cows. Each test day was characterized by a temperature-humidity index (THI1) for whose calculation at 15 hours – at the end of the warmest period – the data were registered. The cows water intake and milk production were measured, as well as the external body temperature, the pulse and respiratory rate of the animals were measured once a day, also at 15 hours. The relationship between the measured parameters and the THI1 value was investigated and the correlation between the parameters was studied. The data for each study day (n = 31; THI1 = 63-81) were used for the correlation analysis. The average value of the parameters measured on non-heat stress days (n = 12; THI1 = 63-68; hereafter NHS) and that on heat stress days (n = 17; THI1 = 69-75; hereafter HS) were compared. The cows’ daily water intake (l/cow/day) was 79.4  3.4 (NHS) vs. 84.4  5.2 (HS) (+6.3%; p  0.01). The daily milk production (l/cow/day) was 13.2  0.7 (NHS) vs. 11.9  1.6 (HS) (-9.8%; p  0.01). The external body temperature (C) was 38.4  0.3 (NHS) vs. 38.8  0.3 (HS) (p  0.002). The pulse (1/min) was 67.3  2.6 (NHS) vs. 70.3  2.3 (HS) (p  0.01). The respiratory rate (1/min) was 21.4  0.6 (NHS) vs. 22.0  0.9 (HS) (p  0.1 (NS)). Thus, even in the case of non-intensively bred dairy cattle Hungarian Simmental, which is well adapted to local conditions, an increase in drinking water consumption and a decrease in milk production can be detected already at 69-75 THI1 values. Water intake closely correlated to THI1 (r = 0.84; p  0.001). There is only a moderate correlation between external body temperature and THI1 (r = 0.47; p  0.01). Milk production was more closely related to THI1 (r = -0.84; p  0.001) than to external body temperature (r = -0.59; p  0.001). At the same time, respiratory rate and, in particular, pulse was strongly related to the external body temperature (r = 0.72; p  0.001 and r = 0.92; p  0.001).

heat stress, THI, cattle, Hungarian Simmental, milk production

biology

Presentation: poster