A new heat load index for feedlot cattle

Gaughan, J. B., Mader, T. L., Holt, S. M. and Lisle, A. (2008) A new heat load index for feedlot cattle. Journal of Animal Science, 86 1: 226-234.


Author Gaughan, J. B.
Mader, T. L.
Holt, S. M.
Lisle, A.
Title A new heat load index for feedlot cattle
Journal name Journal of Animal Science   Check publisher's open access policy
ISSN 0021-8812
1525-3163
Publication date 2008-01
Sub-type Article (original research)
DOI 10.2527/jas.2007-0305
Volume 86
Issue 1
Start page 226
End page 234
Total pages 9
Editor S. A. Zinn
Place of publication Savoy, Ill, USA
Publisher Americal Society of Animal Science
Collection year 2009
Language eng
Subject C1
070203 Animal Management
839901 Animal Welfare
Formatted abstract The ability to predict the effects of extreme climatic variables on livestock is important in terms of welfare and performance. An index combining temperature and humidity (THI) has been used for more than 4 decades to assess heat stress in cattle. However, the THI does not include important climatic variables such as solar load and wind speed (WS, m/s). Likewise, it does not include management factors (the effect of shade) or animal factors (genotype differences). Over 8 summers, a total of 11,669 Bos taurus steers, 2,344 B. taurus crossbred steers, 2,142 B. taurus x Bos indicus steers, and 1,595 B. indicus steers were used to develop and test a heat load index (HLI) for feedlot cattle. A new HLI incorporating black globe (BG) temperature (°C), relative humidity (RH, decimal form), and WS was initially developed by using the panting score (PS) of 2,490 Angus steers. The HLI consists of 2 parts based on a BG temperature threshold of 25°C: HLIBG>25 = 8.62 + (0.38 x RH) + (1.55 x BG) – (0.5 x WS) + e(2.4–WS), and HLIBG<25 = 10.66 + (0.28 x RH) + (1.3 x BG) – WS, where e is the base of the natural logarithm. A threshold HLI above which cattle of different genotypes gain body heat was developed for 7 genotypes. The threshold for unshaded black B. taurus steers was 86, and for unshaded B. indicus (100%) the threshold was 96. Threshold adjustments were developed for factors such as coat color, health status, access to shade, drinking water temperature, and manure management. Upward and downward adjustments are possible; upward adjustments occur when cattle have access to shade (+3 to +7) and downward adjustments occur when cattle are showing clinical signs of disease (–5). A related measure, the accumulated heat load (AHL) model, also was developed after the development of the HLI. The AHL is a measure of the animal’s heat load balance and is determined by the duration of exposure above the threshold HLI. The THI and THI-hours (hours above a THI threshold) were compared with the HLI and AHL. The relationships between tympanic temperature and the average HLI and THI for the previous 24 h were R2 = 0.67, P < 0.001, and R2 = 0.26, P < 0.001, respectively. The R2 for the relationships between HLI or AHL and PS were positive (0.93 and 0.92 for HLI and AHL, respectively, P < 0.001). The R2 for the relationship between THI and PS was 0.61 (P < 0.001), and for THI-hours was 0.37 (P < 0.001). The HLI and the AHL were successful in predicting PS responses of different cattle genotypes during periods of high heat load.
Keyword bioclimatic index
beef cattle
feedlot
heat stress
Q-Index Code C1
Q-Index Status Confirmed Code

Document type: Journal Article
Sub-type: Article (original research)
Collection: School of Agriculture and Food Sciences
 
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Created: Thu, 02 Apr 2009, 15:25:05 EST by Mrs Kathy Bachmann on behalf of School of Animal Studies