Physiological indicators of heat stress recorded under environmental conditions in both lactating Holstein and Jersey cows (modified from Lee et al. (2020) for Holstein data). (A) Rectal temperature recorded on the day of sampling. (B) Relative average milk yield (RAMY) to May. (C) Average daily gain (ADG). Statistical significance: *p < 0.05, **p < 0.01, ***p < 0.001.