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Evaluating the onset of heat stress in dairy calves

L. Kovács, F. L. Kézér, P. Póti and others

Journal of Dairy Science (2020) 103, 2707–10

doi: 10.3168/jds.2019-17459

• What did the research find?

The estimated upper critical temperature-humidity index (THI) values based on the assessment of calves’ respiratory rate, rectal temperature, ear temperature, heart rate and salivary cortisol concentrations were 82.4, 88.1, 83.0, 78.3 and 88.8, respectively. This indicates that the welfare of calves may be compromised above a THI of 78 and that calves experience significant heat stress above a THI of 88.

• How was it conducted?

A total of 16 preweaned Holstein bull calves were housed individually in plastic calf hutches with exercise pens. The ambient temperature and relative humidity within the hutches and exercise pens were measured for four days, and the daily THI was calculated. The calves’ respiratory rate, rectal temperature, ear temperature, heart rate and salivary cortisol concentrations were also measured continuously during the same four days. The THI values at which each physiological variable showed evidence of heat stress …

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