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Title: Evaluation of physiological differences in heat tolerant (Romosinuano) and heat susceptible (Angus) Bos taurus cattle during controlled heat challenge.

item SCHARF, B.
item WAX, L.
item Carroll, Jeffery - Jeff Carroll
item Riley, David
item Chase, Chadwick - Chad
item Coleman, Samuel
item KEISLER, D.
item SPIERS, D.

Submitted to: Journal of Animal Science Supplement
Publication Type: Abstract Only
Publication Acceptance Date: 4/2/2007
Publication Date: 7/8/2007
Citation: Scharf, B., Wax, L.E., Carroll, J.A., Riley, D.G., Chase, C.C., Coleman, S.W., Keisler, D.H., Spiers, D.E. 2007. Evaluation of physiological differences in heat tolerant (Romosinuano) and heat susceptible (Angus) Bos taurus cattle during controlled heat challenge.. Journal of Animal Science Supplement. Southern Association of Agricultural Scientists. Journal of Animal Science Supplement. 85(1):Paper No. W9.

Interpretive Summary:

Technical Abstract: A study was performed to evaluate differences in thermoregulatory ability of two Bos taurus breeds with known differences in heat tolerance. Nine Angus (304 ± 7 Kg BW; AG) and nine Romosinuano steers (285 ± 7.5 Kg BW; RO) were housed in the Brody Environmental Center at the University of Missouri. Steers were housed for 14 d at thermoneutrality (21°C; TN) before initiation of heat stress. Heat stress (HS) consisted of daily cyclic air temperature (26°C night; 36°C day) for 14 d. Steers were fed a typical feedlot diet at 1.6% of BW/d. Rectal temperature and respiration rate were measured six times daily. Sweat rates were recorded on specific days throughout the study on shaved shoulder and rump sites. Analysis was repeated measure ANOVA. Respiration rate at TN was higher (P < 0.001) in AG than RO, by ~20BPM. Angus steers maintained a higher rectal temperature (+0.5°C) than RO at TN (P < 0.0001). Sweat rates were also higher at TN (+6g/m2/h; P < 0.03). Both breeds initially increased sweat rate 4-fold during HS (P < 0.0001), followed by reduction after 3 d (P < 0.0001).Sweat rate during HS was higher (P < 0.0001) in AG compared to RO by ~90 g/m2/h. Both breeds increased respiration rate by ~ 30 BPM during HS, with AG steers exhibiting the higher rate (P < 0.0001).Rectal temperature increased during HS for both breeds (P < 0.0001),but was higher in AG breed (P < 0.001). Romosinuano steers exhibit a lower sweat and respiratory rates than AG during HS, while maintaining the lower rectal temperature. Indices of heat loss used in this study suggest that these avenues are not used to generate a lower rectal temperature seen in Romosinuano cattle during heat stress.