RECTAL TEMPERATURE AND GRAZING TIME IN SELECTED BEEF-CATTLE BREEDS UNDER TROPICAL SUMMER CONDITIONS IN SUBTROPICAL FLORIDA

Rectal temperature, an index of heat tolerance, was investigated in Se nepol, Brahman, Angus, and Hereford cows and heifers, and Senepol, Her eford, and Senepol-Hereford crossbred (S x H and H x S) calves under t ropical summer conditions in subtropical central Florida. Grazing acti vity in Senepol and Hereford cows also was investigated. Rectal temper atures was affected (P < 0.01) by breed in cows, heifers, and calves w ith Angus and Hereford generally displaying higher rectal temperatures than Senepol and Brahman. Hereford calves that were clipped to simula te a short hair coat had rectal temperatures intermediate between Here ford calves with long hair and Senepol calves with short hair. Crossbr ed Senepol x Hereford calves had a short hair coat similar to pure-bre d Senepol and had rectal temperatures lower (P < 0.01) than Hereford c alves and usually not different from Senepol calves. Mean daily grazin g time within breeds was similar between years but was longer (P < 0.0 5) for Senepol cows (10.5-10.7 h) than for Hereford cows (9.3 h). Resu lts suggest a higher degree of heat tolerance in Senepol cattle relati ve to temperature breeds, represented by Angus and Hereford in this st udy. Furthermore, this heat tolerance may have been responsible for th e difference in average daily grazing time observed between Hereford a nd Senepol cows because rectal temperature was negatively associated w ith grazing time.