This investigation was carried out, using three dry and three lactating fistulated Holstein cows, to determine the effect of environmental temperature on the water vaporization of dairy cows given high concentrate ration. Water vaporization in dairy cows was estimated by determining the difference between total water intake and total water loss except water vaporization. The ration was made up of concentrate (mainly corn) and hay in a ratio of 7 : 3 on a dry matter basis and each animal received 120% of the calculated maintenance TDN requirement. The cows were housed in a climate controled chamber and subjected to four temperature treatments of 18℃-8 days, 26℃-8 days, 32℃-8 days and 36℃-7 days (lactating cows; 36℃-4 days). The relative humidity was maintained at 60% throughout the experiment. The results are as follows : l) There was a positive significant correlation (r=0.886) between drinking water intake and body temperature in dry cows. In lactating cows drinking water intake decreased during 36℃ period as compared with the 32℃ period although body temperature increased significantly. 2) There were significant differences in the amount of water in the urine of dry cows between treatments and this increased with increases in environmental temperature. However there was no significant difference in the amount of water in the urine of lactating cows. 3) There was no significant difference in the amount of water in the feces of dry cows between treatments. But there was a significant difference in that of lactating cows. The amount of water in the feces of lactating cows decreased with increases in environmental temperature. 4) There were no significant differences in the rate of water vaporization in dry cows between treatments although it had a tendency to increase with increases in environmental temperature. A significant difference in the rate of water vaporization was observed in lactating cows, which increased with increases in environmental temperature till the 32℃ period and decreased during the 36℃ period. 5) The rate of water vaporization in dry and lactating cows was affected considerably by environmental temperature and drinking water intake. Results from multiple regression analyses suggested that there was a possibility that the rate of water vaporization could be estimated from these two facters.

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To investigate the relationships between the diurnal cycle of air temperature and diurnal rhythms of physiological responses, heart rate, respiration rate and rectal temperature of lactation cows were measured under the conditions of 18℃ constant temperature, 25.5-32.5℃ variable temperature and 22-32℃ variable temperature. The results indicated that l) heart rate was increased after feeding under constant temperature, but under variable temperature, this change in heart rate after feeding was not so clear and no correlation between air temperature and heart rate rate was observed; 2) there was no obvious tendency of respiration rate under constant temperature, but a close positive relationship was observed between air temperature and respiration rate under variable temperature; 3) under constant temperature, rectal temperature was increased only after feeding and under variable temperature the change in rectal temperature was delayed to the change of air temperature; 4) the phase difference between air temperature cycle and respiration rhythm was 1-2 hours and between air tempera ure and rectal temperature was 3-6 hours.

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