The Thai Journal of Veterinary Medicine


The objective of this study was to assess the relationship of temperature-humidity index (THI) with milk production, feed intake and feed efficiency of Holstein-Frisian cows in different seasons of the year. Five hundred and sixty three cows were monitored in spring, 557 cows in summer, 594 cows in autumn and 567 cows in winter, for a total period of two years. In contrast to the spring, autumn and winter periods, the summer period was characterized by heat stress conditions. Average T and THI exceeded the 25°C and 72 critical points, respectively, on all, 90% and 93% of test days for this period, indicating that the cows were exposed to heat stress during the summer trial. The heat stress reduced daily milk yield by 1.32 kg or 9.46%, by 0.92 kg or 9.62% and by 1.27 kg or 9.48% as the THI values went from 64 in the spring, from 66 in the autumn and from 42.34 in the winter periods to 79 in the summer period. Forage intake was decreased by 1.63 kg, by 1.42 kg and by 1.25 kg compared to those in spring, autumn and winter, respectively, and the efficiency of conversion of feed to milk was increased (from 1.6 to 1.59 kg milk/kg milk). The regression equation obtained under the conditions of the present work indicates that daily milk yield drops, daily forage intake drops per cow per day and food efficiency increases per kg food when the value of THI increases. In conclusion, summer heat stress negatively affects milk yield and forage intake of dairy cows. Therefore, management strategies are needed to minimize the heat stress and attain optimal dairy cow productivity.

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