Effect of high temperature on milk production of cows from free-stall housing with natural ventilation

Abstract

Aim of the present work was to study the influence of high temperatures on milk production of dairy cows. This work tested the hypothesis that the milk yield of Holstein cows kept in open barn is affected by the month, stage of lactation and parity of dairy cows. Following stages were stated in 193 heads: Stage 1, from parturition to 50 d; Stage 2, from 51 to 120 d; Stage 3, from 121to 200 d. Sixty-three summer and 14 tropical days, 86 days with the THI above 72.0, and 26 days with the THI above 78.0, from May to September were recorded. The milk production of dairy cows of Stage 1 was significantly affected by high temperatures for 305 days of lactation than the cows in the Stage 2 (8954.4 kg vs. 9614.1 kg; P<0.05). The monthly milk yields of Stage 1 gradually increased from May to July (from 33.94 kg to 36.62 kg) and started decreasing through August (32.26 kg) to September (30.05 kg). Decrease of milk yield between July and August was significant in Stage 1 (July 36.62 kg vs. August 32.26 kg; P<0.01). Very highly significant differences were found among parities in the index of persistency (P<0.001).