| Popis: |
Tympanic temperature and respiratory dynamics of 240 yearling steers were used to assess 3 housing systems in South Dakota during summer (69 d). The housing systems were full confinement (CONF), open lot (OPN), and partial confinement (PTL). Steers were randomly allocated in equal numbers to each system (1 pen/system). Ambient temperature, black globe temperature (BG), solar radiation, wind speed, wind direction, and relative humidity were recorded at 30-min intervals from a weather station. A modified temperature-humidity index {THIMOD = (0.8 × BG) + [(relative humidity/100) × (BG − 14.4)] + 46.4} was used to assess thermal load. Panting score (0 = normal to 4 = open-mouth panting, tongue out, and excessive drooling) of each animal was recorded at 0600, 1200, and 1600 h. Mean panting score (MPS) of steers in OPN (0.563) was greater than MPS of PTL (0.383;P = 0.06) and CONF (0.278;P = 0.003) steers. There were no MPS differences (P > 0.05) between CONF and PTL. During extreme events (THIMOD ≥84), the MPS of OPN (1.30) was greater (P 1.2 indicates an extreme heat load. Tympanic temperature was recorded from 10 animals/treatment during 3 heat waves of 8, 8, and 6 d duration. When THIMOD ≥84, the mean tympanic temperature for OPN (40.55°C) was greater (P < 0.05) than those of PTL (40.04°C) and CONF (40.02°C). Under the climatic conditions encountered, it is evident that the housing systems that offered shade (CONF and PTL) reduced the effects of extreme heat load on feedlot cattle. |
