Abstract
Five hundred and seventy four Bos Taurus steers (Angus, Hereford and Murray Grey) were used in a study to determine the effect of high heat load on performance and carcass characteristics when fed a high energy diet for 165-183 days. The trial was undertaken at a commercial feedlot between December 2002 and June 2003. Regardless of coat colour, body surface temperature of feedlot cattle rose (P<0.05) as climatic conditions changed from thermoneutral (Temperature and Humidity Index (THI)<74) to moderate (THI 74-77). Under extremely hot conditions, body surface temperature was higher (P<0.05) for Angus compared with Murray Grey (43.4°C and 38.4°C, respectively) steers. Murray Grey steers had greater average daily gain than either Angus or Hereford. There were no differences between breeds for carcass weight, eye-muscle area and marbling score. However, Murray Grey steers had an ideal subcutaneous fat coverage, and in terms of reduced labour costs, Murray Grey steers could be economically more efficient than either Angus or Hereford steers.
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