EFFECT OF UTILIZING EVAPORATIVE COOLING IN TIESTALL DAIRY BARNS EQUIPPED WITH TUNNEL VENTILATION ON RESPIRATION RATES AND BODY TEMPERATURE OF LACTATING DAIRY CATTLE

摘要

During the summer of 2001, six tie-stall dairy barns in northeast Missouri were monitored to determine the effects of evaporative cooling on the environment, respiration rate and body temperature of lactating dairy cattle housed in barns equipped with tunnel ventilation. Temperature and relative humidity were continuously monitored and recorded every 15 minutes in six barns (3 with and 3 without evaporative cooling systems) for a three-month period. Temperature and relative humidity data were averaged by hour prior to statistical analysis. Respiration rate, infrared skin temperature and rectal body temperature of 20 animals per barn (10 primiparous and 10 multiparious) were measured on three different days during summer heat stress. Measurements were simultaneously taken between 7-8 am, 4-5 pm and 10-11 pm on each of the three days. Cattle housed in evaporative cooled tunnel ventilated barns had lower (P<0.05) afternoon and evening respiration rates and body temperatures than those housed in barns without evaporative cooling. Evaporative cooling reduced (P<0.05) afternoon barn temperatures, however relative humidity increased (P<0.05) as compared to barns with only tunnel ventilation. Evaporative cooling in conjunction with tunnel ventilation reduced afternoon heat stress of dairy cattle housed in tie-stall barns. High environmental relative humidity reduced the cooling capacity of the evaporative cooling, however on the days of animal observation it reduced heat stress of lactating dairy cattle.