according to numerous studies evaluating cattle’s performance under heat stress as a way of measuring heat tolerance. These metrics include:
- Heart rate -
- Sweating ability / rate - Sweating ability impacts heat tolerance (Dowling, 1958; Finch et. al, 1982); Differences in sweating rates were statistically significant (P < 0.05) (1) between breeds, (2) between black and white hair coats, and (3) with changes in solar load, relative humidity, and air velocity. When the humidity is high, the sweat on longer haired cattle has a difficult time evaporating.
- Respiration rate / Panting score - Using a panting scale of 0 to 4.5 to measure stress, bos taurus feedlot cattle scored 2 points worse than bos indicus cattle.
- Body temp / Rectal temperature - Rectal temperature is easily measured and a valid indicator of heat tolerance. Bos indicus cattle displayed lower rectal temperatures than Bos taurus breeds when grazing under high ambient temperatures (Cartwright, 1955; Turner, 1984). Angus and Hereford cattle displayed higher rectal temperatures than Senepol and Brahaman cattle.
- Body surface to mass ratio - related to cattle’s ability to dissipate internal heat (Carabano et al, 2019; Gray et al, 2001)
- Shedding - Shedding rate is related to cattell's ability to dissipate internal heat Carabano et al, 2019; Gray et al, 2001)
- Hair length - Hereford cattle that were clipped to simulate a short hair coat had a rectal temperature lower than un-clipped Herefords but higher than Senepol cattle with natural short hair coats. Senepol cross cattle had similar hair length as pure bred Senepol and similar rectal temperatures. (Hammond)
- Grazing time - Senepol and Zebu cattle grazed longer hours and during hotter parts of the day as compared to Herford, Charolais and Angus cattle. (Hammond)