ALLEVIATION OF HEAT STRESS FOR HOLSTEIN LACTATING COWS IN HOT SUMMER BY A WET-PADDING BARN

Heat stress resulted from high temperature (T) and relative humidity (RH) is an obstacle that limits the development of livestock industry in Taiwan. Feasibility of using a wet-padding (WP) barn to alleviate heat stress for Holstein lactating cows was assessed. Cows fed in the conventional (C) free stall barn were designated to be control group. Eight exhaust fans set at one end of WP barn drew the air through water padding at the other barn end and cooled the barn T. Maximum air exchange velocity achieved twice per minute. There were four fans and time-set sprinkling to cool the C barn. In hot summer of 2005, average daily T inside WP and C barns were 26.6℃ and 27.8℃, and RH were 97.6% and 88.5%, respectively. Cow responses and performance raised in these two barns were studied in a crossover design with 30 days a period and a total of 42 lactating cows. Results indicated that WP environment increased heat load of cows. Respiration rate at 4 a.m. (62.2 vs. 49.8 times per min, P < .001), rectal T at 4 a.m. (39.58 vs. 39.31℃, P < .01) and 2 p.m. (39.75 vs. 39.47℃, P < .03) were all increased. Moreover, WP barn lowered the dry matter intake by 7.6% (17.0 vs. 18.4 kg), milk yield by 9.3% (23.3 vs. 25.7 kg, P < .001), milk protein percentage (3.27 vs. 3.33%, P < .05), milk total solid percentage, and intake activity after p.m. feed was offered (35.7 vs. 62.1%, P < .05). Although WP barn could decrease T more efficient than C barn, persistently high RH (≥ 93.5%) might restrict heat release by way of surface skin and thus cause the higher body T and lower performance. More WP design studies focusing on decreasing RH is necessary.