Submitted to: Biosystems Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 2, 2005
Publication Date: May 8, 2005
Citation: Eigenberg, R.A., Brown Brandl, T.M., Nienaber, J.A., Hahn, G.L. 2005. Dynamic response indicators of heat stress in shaded and non-shaded feedlot cattle: part 2 predictive relationships. Biosystems Engineering 91(1):111-118. Interpretive Summary: Summer heat provides stressful conditions for Bos taurus feeder cattle; in extreme instances these conditions can be fatal. One management option is to provide shade structures for feedlot animals. Respiration rate, feed intake, and body temperature were measured for animals having access to shade and those with no shade available. Environmental conditions were monitored for the experimental period. The resultant data demonstrated thresholds between 25 and 30 deg C for dew point and treatment of shade/no-shade. An equation was developed for respiration rate that includes the effect of temperature, dew point, wind speed, and solar radiation. This equation gives estimates of stressful conditions for cattle under hot conditions.
Technical Abstract: Summer heat provides stressful conditions for Bos taurus feeder cattle; in extreme instances these conditions can be fatal. One management option is to provide shade structures for feedlot animals. This study was conducted during the summer of 2001 to compare physiological responses of cattle with shade access (SA) or no-shade access (NS). Eight steers were selected from a group of 12 and assigned individual pens. Four pens were fitted with shade structures that allowed the steers to choose shade; the remainder had no shade option. The animals were rotated through pen assignments during the summer season. Continuous measures of respiration rate (RR) and body temperature, along with daily feed intake, were recorded as response variables to the shade treatments. Environmental conditions were monitored for the experimental period. Daytime means and standard errors were 86.0 +/- 0.39 breaths per minute (bpm) for RR shade and were significantly lower (P<0.05) than RR no shade of 102.3 +/- 0.36 bpm. Linear regression fit for daytime data showed the slope for NS to be 4.5 +/- 0.15 bpm per deg C and 1.5 +/- 0.11 bpm per deg C for SA. The data demonstrated thresholds for humidity and treatment of SA/NS at 25 deg C. Linear regression equations were developed for RR including effects of temperature, humidity, wind speed and solar radiation for animals in either SA or NS feedlot pens.