Critical Temperature-Humidity Index Thresholds for Dry Cows in a Subtropical Climate

The effects of heat stress on dry cows are profound and significantly contribute to lower overall welfare, productivity, profitability the dairy sector. Although more thermotolerant than lactating due their non-lactating state, similar environmental thresholds currently used estimate degree strain cooling requirements. Records cow studies conducted over 5 years in Gainesville, Florida, USA were pooled analyzed determine at which exhibit signs a subtropical climate. Dry-pregnant multiparous dams actively cooled (CL; shade freestall barn, fans water soakers, n = 107) or not (HT; only, 111) during last 7 weeks gestation, concurrent with entire period. Heat indices, including ambient temperature, relative humidity, temperature-humidity index (THI), animal-based respiration rate, rectal temperature daily matter intake recorded all studies. Simple correlations performed between each indicator. Differences treatments by multiple regression. Using segmented regression, for significant changes indicators estimated. Stronger found indices measured HT (?0.22 ? r 0.35) CL (?0.13 0.19). exposed index, (+0.3°C; P < 0.001) rate (+23 breaths/min; elevated compared whereas (?0.4 kg matter/d; 0.003) was reduced. Temperature-humidity began change both determined THI 77 cows. No threshold detected intake. At practical level, our results demonstrate that increased abruptly when provided only managed Therefore, absence active cooling, should be closely monitored before reaches avoid further heat-stress related impairments period subsequent lactation mitigate potential carry-over offspring.