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

Autor:	Davidson BD; Department of Animal Sciences, University of Florida, Gainesville, 32608., Dado-Senn B; Department of Animal Sciences, University of Florida, Gainesville, 32608., Padilla NR; Department of Animal Sciences, University of Florida, Gainesville, 32608., Fabris TF; Department of Animal Sciences, University of Florida, Gainesville, 32608., Casarotto LT; Department of Animal Sciences, University of Florida, Gainesville, 32608., Ouellet V; Department of Animal Sciences, University of Florida, Gainesville, 32608., Toledo IM; IFAS Extension, University of Florida, Gainesville, 32603., Dahl GE; Department of Animal Sciences, University of Florida, Gainesville, 32608., Laporta J; Department of Animal Sciences, University of Florida, Gainesville, 32608. Electronic address: jlaporta@wisc.edu.
Jazyk:	angličtina
Zdroj:	Journal of dairy science [J Dairy Sci] 2021 Feb; Vol. 104 (2), pp. 2357-2368. Date of Electronic Publication: 2020 Nov 25.
DOI:	10.3168/jds.2020-18998
Abstrakt:	Multiparous, nonlactating pregnant cows are negatively affected by heat stress, but the effect of heat stress on more thermotolerant pregnant heifers has received less attention. Our objective was to characterize the effect of late-gestation heat abatement on thermoregulatory responses and subsequent milk production of nulliparous Holstein heifers. Pregnant heifers, blocked by body condition score (BCS) and predicted transmitting ability (PTA) for milk, were enrolled in either heat stress (HT, shade of freestall barn; n = 16) or cooling (CL, shade of freestall barn, water soakers, and fans; n = 15) environments during the last 60 d of pregnancy (~8 weeks). Rectal temperature (RT; thermometer), respiration rate (RR; breaths/min), sweating rate (SR; VapoMeter, Delfin Technologies, Kuopio, Finland), and skin temperature (ST; infrared thermometer) were measured thrice weekly from enrollment to calving. Vaginal temperature (VT; i-button intravaginal device) was measured every 10 min for 7 consecutive days at wk -8, -6, -4, and -2 relative to calving and averaged hourly. Daily thermoregulatory patterns assessed by SR and ST, were measured every 4 h over a 36-h time interval at wk -6, -4, and -2 relative to calving. Upon calving, milk, protein, and fat yields were recorded twice daily for 15 wk. The average temperature-humidity index (Hobo Pro temperature probe, Onset Computer Corporation, Pocasset, MA) in the barn during the precalving period was 77 (minimum of 72, maximum of 82). Only heifers that gave birth to a female calf (CL = 12, HT = 14) were included in the statistical analysis. In the precalving period, CL heifers had lower RR (44.3 vs. 60.0 ± 1.6 breaths/min), RT (38.7 vs. 38.8 ± 0.04°C), unshaved ST (34.7 vs. 35.3 ± 0.17°C), and unshaved SR (19.0 vs. 35.2 ± 1.9 g/m 2 h), relative to HT heifers. Additionally, VT was lower in CL heifers during wk -4, and -2, specifically during early morning and early afternoon hours. When measured over a 36-h time interval, ST and SR were lower in CL heifers, when compared with HT heifers for all weeks. Notably, ST was reduced overnight and SR was reduced during the daytime. Cooled heifers had higher milk yield (35.8 vs. 31.9 ± 1.4 kg/d), when compared with HT heifers. Similar to multiparous cows, our data indicate that actively cooling heifers in late pregnancy is effective in promoting thermoregulation and results in elevated milk production postcalving. (Copyright © 2021 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)
Databáze:	MEDLINE
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