Genetic parameters and breeding values for daily milk production of Holstein cows in terms of heat stress

Abstract

In order to estimate the variance components as well as the breeding value for daily milk production of Holstein cows in terms of heat stress defined as different THI threshold values (68, 70, and 72) 1,275,713 test-day records from 90,159 cows were used. Temperature-humidity index (THI) calculated from ambient temperature and relative humidity recorded in the barns on the milk recording day was used as the measure of heat stress. Daily milk production was analysed as a bivariate variable, in the normal conditions (under the set THIthreshold value), and in terms of heat stress (above the set THIthreshold value) using a model that accounted variances due to lactation stage, calving season, age at calving, breeding region, parity, permanent environment, interaction between hear and year, and individual animal. The estimated high genetic correlations between the daily milk production in normal and heat stress conditions, as well as high correlations among the EBVs in normal and heat stress conditions, point out that Holstein cows with high productivity in normal condition will sustain an alike level of production even in terms of heat stress. These results indicate that the Holstein cows are very well acclimatized to the environmental conditions at dairy farms in Croatia. However, these findings should be taken with caution, given that measurements of microclimate parameters were conducted only once at a milk recording day, so the reliability of such measurements could be questionable. In conclusion, in order to realize a completely unambiguous conclusion, further studies that include multiple daily measurements of microclimatic parameters in the farms facilities are necessary.

The effect of animal-related and some environmental effects on daily milk production of dairy cows under the heat stress conditions

“…LSMeans of the analysed daily milk traits depending on the cow's breed show that the highest daily milk yield was achieved by Holstein-Friesian cows with an average of 19 2007) determined that the level of heat stress may also depend on the animal's body cover, with lower resistance in black cows. The highest daily milk production traits determined in Holstein breeds indicate that high productive animals will tend to maintain high production even in heat stress conditions which are in agreement with the results of Vučković et al (2020).…”

“…Kadzere et al (2002) obsereved that moderate levels of heat stress occur at THI values ≥72 when the first physiological adaptations, decreased productivity and pathophysiological changes occur, while other studies confirmed that it also occurs at THI values ≥68 (Bernabucci et al, 2010;Brugemann et al, 2012;Hammami et al, 2015). Some authors define a threshold at which dairy cows begin to physiologically adapt to the harmful effects of heat stress when THI reaches 68 (Allen et al, 2015), so the values of 68 and 72 were defined as the THI threshold for heat stress in lactating dairy cows (Anderson et al, 2013;Vučković et al, 2020). Globally, scientists report ubiquitous climate changes and the negative effects of heat stress on cattle (Nardone et al, 2010), where, additionally to temperature changes, solar radiation can significantly contribute to the accumulation of body heat.…”