Effect of drinking water temperature on heat stress of dairy cows.

Experiments were to determine the effectiveness of chilled drinking water in reducing heat stress of lactating dairy cows. Using a 4 X 4 Latin square statistical design, 16 cows (4/treatment) were deprived of water from 0800 until 1400 h at which time they were given chilled water (10, 16, 22 degrees C) or a control water (28 degrees C) ad libitum. Cows were rotated weekly among treatments. Eight of the cows (2/treatment) were selected at random and monitored continuously for body temperature measured in the middle ear near the tympanic membrane. The coldest water (10 degrees C) reduced body temperature (.75 degrees C) more than 28 degrees C water (.46 degrees C). The coldest water also reduced respiration rate and kept body temperatures lower longer. Chilled water was only about 32% effective in reducing body temperature, and it is doubtful if the effect was prolonged enough (about 2 h) to keep the body temperature of cows from rising above the critical temperature of thermoneutrality. Offering chilled water at milking time may provide an incentive for the cows to enter the milking parlor.