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Title:   Author  item
                                            SCHARF, B - University Of Missouriitem
                                            Carroll, Jeffery

                                                         - *Jeff Carroll*item
                                            RILEY, D - Texas A&M Universityitem
                                            Chase, Chadwick

                                                         - *Chad*item
                                            Coleman, Samuelitem
                                            KEISLER, D - University Of Missouriitem
                                            WEABER, R - University Of Missouriitem
                                            SPIERS, D - University Of Missouri
  Submitted to: Journal of Animal Science
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 1/7/2010
                                    Publication  Date: 2/26/2010
                                    Citation: Scharf, B., Carroll, J.A., Riley, D.G., Chase, C.C., Coleman, S.W., Keisler, D.H., Weaber, R.L., Spiers, D.E. 2010. Evaluation of Physiological and blood serum differences in heat tolerant (Romosinuano) and heat susceptible (Angus) Bos taurus cattle for determination of markers of sensitivity. Journal of Animal Science.  88:2321-2336, and doi:10.2527/jas.2009-2551Interpretive Summary: Development of cattle that can tolerate heat stress and maintain productivity has been a long-term goal of researchers and cattle breeders. Historically, most research in this area has emphasized comparisons of heat tolerant Bos indicus cattle (e.g., Brahman) vs. heat susceptable Bos taurus cattle (e.g., Angus).  However, isolation of specific differences in thermoregulatory ability is challenging due to the many physical and genetic differences
that could have secondary influences. Current interest has shifted toward using breeds of Bos taurus cattle from tropical climates that might be both heat tolerant compared to British cattle and superior to Bos indicus cattle in terms of reproduction, growth, and carcass quality. The Romosinuano is a tropically adapted criollo beef breed that is native to Colombia, South America that exhibits heat tolerance, and are purported to have good fertility and carcass merit.  The purpose of this study was to compare the thermoregulatory response of Romosinuano cattle with that of a heat sensitive Bos taurus breed (Angus).  We used a controlled heat challenge at the Brody Environmental Center at the University of Missouri to derive potential physiological and/or biochemical indicators of heat tolerance.  After 18 days at thermoneutrality (21°C;  TN) the steers were subjected to a heat stress environment that consisted of daily cyclic air temperature (26°C night: 36°C day) for 14 days. Rectal temperature, sweating rate, and respiration rate were measured.  Blood samples were taken once a week and analyzed for serum prolactin, leptin, creatinine, and cholesterol. Angus steers maintained 0.5°C higher rectal temperature and had higher respiration and sweat rates than Romosinuano at thermoneutrality.  During heat stress, rectal temperature and respiration rate increased for both breeds, and were still higher in Angus in Romosinuano.  Sweat rate increased more than 4-fold during heat stress, followed by reduction after 7 days, and rates were always higher in Angus.  Serum leptin, prolactin, creatinine, and cholesterol were higher in Angus steers than Romosinuano during heat stress throughout the study and Angus steers exhibited a heat-stress induced increase in these metabolites.  Use of rectal temperature along with endocrine markers such as prolactin may aide in the identification of sensitivity to heat in cattle.
                                Technical Abstract: Two Bos taurus breeds with known differences in heat tolerance were tested under controlled conditions to evaluate heat tolerance.    Romosinuano (RO) is a tropically adapted breed. Nine Angus (304 ± 7 Kg BW; AG) and nine RO (285 ± 7.5 Kg BW) steers from USDA-ARS, Brooksville, Florida were transported to the Brody Environmental Center at the University of Missouri. Steers were housed for 14 days at thermoneutrality (21C; TN) before 14 days of cyclic heat stress (HS; 26C night; 36C day). Rectal temperature and respiration rate were measured six times daily. Sweat rates at shaved sites were recorded on specific days. Blood samples were taken once a week. The RO maintained a lower respiration rate (20 bpm), sweat rate (6 g/m2/h), and rectal temperature (0.5C) than AG throughout TN. Both breeds increased sweat rate, respiration rate, and rectal temperature during HS, with AG retaining the higher levels. There were breed differences for serum prolactin, leptin, creatinine, and cholesterol, with AG being higher than RO. Serum leptin increased for both breeds with HS. Although there were no breed differences at TN, AG steers exhibited HS-induced increases in prolactin, creatinine, and cholesterol. However, these measures for RO were unaffected by HS. The present study has identified additional physiological and endocrine markers that may aide in the identification of Bos taurus sensitivity to heat.  The reasons for these changes during heat stress remain to be determined.


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