Chilled drinking water effects on lactating Holstein cows in summer.

In Experiment 1, 12 multiparous lactating cows (six per group) were offered drinking water ad libitum at temperatures of 10 or 30 degrees C in a switchback design. The treatment group received 10 degrees C water from 1235 to 2000 h and was then changed to 30 degrees C water for the remaining 16.5 h/d. The control group received 30 degrees C water 24 h/d. Respiratory rates, rectal temperatures, and rumen motilities were measured at 1100, 1440, and 1810 h, 3 d/wk. Water consumed was recorded for 1235 to 2000 h and 2001 to 1234 h of the next day. Water consumption for the treatment group was 3.90 L/h per cow compared to 5.40 L/h per cow for the control group from 1235 to 2000 h. However, the 10 degrees C water absorbed 65.6 kcal/h more heat than the 30 degrees C water. No differences were found in respiratory rates, rectal temperatures, rumen motilities, or milk yield. Cows that drank 10 degrees C water consumed 3.67 kg of feed DM/100 kg of body weight compared with 3.36 kg of feed for the controls. In Experiment 2, the same two groups of cows were offered 9.5 degrees C water ad libitum for 24 h/d or 27.5 degrees C water for a 48 h comparison. The treatment group tended to consume more water than the control group and to have lower respiratory rates and body temperatures.