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Heat stress abatement for late-gestation dairy heifers improves thermoregulation and productivity.

B. D. Davidson


Heat stress abatement for late-gestation dairy heifers improves thermoregulation and productivity.
B. D. Davidson*, B. Dado-Senn, N. Rosa Padilla, T. F. Fabris, L. T. Casarotto, V. G. Ouellet, G. E. Dahl, J. Laporta. Department of Animal Sciences, University of Florida Gainesville, FL.

Multiparous cows are negatively impacted by heat stress when dry, however, the impact of heat stress on pregnant heifers has received less attention. Our goal was to determine if late gestational heat stress abatement improves thermoregulatory responses and milk production of nulliparous heifers. Pregnant heifers were randomly assigned to either heat stress (HT, shade; n = 16) or cooling (CL, shade, soakers, and fans; n = 15) environments during the last 60 d of pregnancy (~8 weeks). Rectal temperatures (thermometer), respiration rates (flank movements/min), sweating rates (SR; VapoMeter), and skin temperatures (ST; infrared thermometer) were measured thrice weekly from enrollment to calving. Vaginal temperatures (i-button intra-vaginal device) were measured every 10 min for 7 consecutive days at wk 1, 3, 5, and 7 relative to enrollment. Daily thermoregulatory patterns were assessed by SR and ST measured every 4 h over a 36-h time interval at wk 3, 5, and 7. Milk yield was recorded twice daily for 15 weeks. Data were analyzed by PROC MIXED (repeated measures) with treatment, hour, week, and all possible interactions as fixed effects. Cool heifers had lower (all P ≤ 0.01) rectal temperatures (38.7 vs. 38.9�C), respiration rates (46.3 vs. 59.6 bpm), and ST (34.8 vs. 35.3�C) relative to HT heifers. Sweating rates were lower in the CL vs. HT heifers from wk 2 to 8 (P < 0.0001). Vaginal temperatures were lower (P = 0.002) in CL relative to HT heifers during wk 1, 3, and 7, particularly between 1000 h to 1400 h and 2200 h to 0500 h. When measured continuously over a 36-h time interval ST and SR were lower (P ≤ 0.006) in CL heifers for all weeks; notably, CL heifer ST was reduced overnight and SR was reduced during the daytime. Cooled heifers had higher milk yield (3.7 kg/d, P = 0.05) when compared with HT heifers during all weeks except wk 2 and 5, in which there was a tendency (P ≤ 0.08) for higher milk production in CL heifers. Similar to multiparous cows, our data indicate that actively cooling heifers in late pregnancy is effective in improving thermoregulation and production.

Keywords: cooling, heifer, milk yield.

Biography: Brittney is a graduate student (MS) at the University of Florida, Department of Animal Sciences. Her thesis is focused on late-gestation heat stress effects on nulliparous heifers (i.e., milk yield and components, health, growth, immune function and behavior) and their offspring.