Abstract
Rectal temperature, an index of heat tolerance, was investigated in Senepol, Brahman, Angus, and Hereford cows and heifers, and Senepol, Hereford, and Senepol-Hereford crossbred (S × H and H × S) calves under tropical summer conditions in subtropical central Florida. Grazing activity in Senepol and Hereford cows also was investigated. Rectal temperature was affected (P < 0.01) by breed in cows, heifers, and calves with Angus and Hereford generally displaying higher rectal temperatures than Senepol and Brahman. Hereford calves that were dipped to simulate a short hair coat had rectal temperatures intermediate between Hereford calves with long hair and Senepol calves with short hair. Crossbred Senepol × Hereford calves had a short hair coat similar to purebred Senepol and had rectal temperatures lower (P < 0.01) than Hereford calves and usually not different from Senepol calves. Mean daily grazing time within breeds was similar between years but was longer (P < 0.05) for Senepol cows (10.5-10.7 h) than for Hereford cows (9.3 h). Results suggest a higher degree of heat tolerance in Senepol cattle relative to temperate breeds, represented by Angus and Hereford in this study. Furthermore, this heat tolerance may have been responsible for the difference in average daily grazing time observed between Hereford and Senepol cows because rectal temperature was negatively associated with grazing time.
