Late-gestation heat stress abatement in dairy heifers promotes thermoregulation and improves productivity

Multiparous, nonlactating pregnant cows are negatively affected by heat stress, but the effect of stress on more thermotolerant heifers has received less attention. Our objective was to characterize late-gestation abatement thermoregulatory responses and subsequent milk production nulliparous Holstein heifers. Pregnant heifers, blocked body condition score (BCS) predicted transmitting ability (PTA) for milk, were enrolled in either (HT, shade freestall barn; n = 16) or cooling (CL, barn, water soakers, fans; 15) environments during last 60 d pregnancy (~8 weeks). Rectal temperature (RT; thermometer), respiration rate (RR; breaths/min), sweating (SR; VapoMeter, Delfin Technologies, Kuopio, Finland), skin (ST; infrared thermometer) measured thrice weekly from enrollment calving. Vaginal (VT; i-button intravaginal device) every 10 min 7 consecutive days at wk −8, −6, −4, −2 relative calving averaged hourly. Daily patterns assessed SR ST, 4 h over a 36-h time interval Upon calving, protein, fat yields recorded twice daily 15 wk. The average temperature-humidity index (Hobo Pro probe, Onset Computer Corporation, Pocasset, MA) barn precalving period 77 (minimum 72, maximum 82). Only that gave birth female calf (CL 12, HT 14) included statistical analysis. In period, CL had lower RR (44.3 vs. 60.0 ± 1.6 RT (38.7 38.8 0.04°C), unshaved ST (34.7 35.3 0.17°C), (19.0 35.2 1.9 g/m2h), Additionally, VT −2, specifically early morning afternoon hours. When interval, when compared with all weeks. Notably, reduced overnight daytime. Cooled higher yield (35.8 31.9 1.4 kg/d), Similar multiparous cows, our data indicate actively late is effective promoting thermoregulation results elevated postcalving.