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Pasture housing increases heat stress in late pregnant heifers: Management challenges for productivity and health.

I. M. Toledo

Events

06-22-2020

Abstract:

59
Pasture housing increases heat stress in late pregnant heifers: Management challenges for productivity and health.
I. M. Toledo*, B. D. Davidson, V. Ouellet, G. E. Dahl, J. Laporta. University of Florida Gainesville, FL.

Exposure of dairy cows to heat stress during late gestation negatively impacts productivity and efficiency. Whereas cooling of dry cows is well accepted, late gestation heifers are often exposed to pasture management and thus heat stress. A better understanding of how heat stress affects the daily time budget of late gestation dairy heifers may aid in the management of these animals in adverse environmental conditions. Holstein heifers were either housed on pasture (PA; n = 6) or in a freestall barn and enrolled to heat stress (HT; shade; n = 6) or cooling (CL; shade, soakers and fans; n = 5) treatments. Automated monitoring devices (Nedap, Netherlands) were used to document behavioral activity. Heifers received a leg tag to measure daily lying time, number of steps and standing bouts and a neck tag to measure eating and rumination time. Temperature-humidity index (THI) and black globe temperature (BG) were recorded. Respiration rates (RR; breaths per min, bpm) were recorded thrice weekly for all groups. Average THI was 78 and BG was 29�C during the study period. RR were greater (P < 0.01) in PA and HT (96 and 61 bpm) compared with CL (48 bpm). Pasture heifers spent more time eating relative to HT and CL (270 � 16.3 vs 163 � 16.30 and 158 � 18.0 min/d; P < 0.01) Rumination time was lower in PA compared with CL (357 � 21.3 vs 438 � 23.4 min/d; P = 0.05), but no difference was observed between PA and HT (P = 0.48). Pasture heifers spent less time lying down compared with CL and HT (582 � 26.0 vs 837 � 28.0 and 784 � 24.2 min/d; P < 0.01). Furthermore, the number of steps was greater for PA compared with CL and HT heifers (5097 � 184 vs 2060 � 200 and 2159 � 179 steps; P < 0.01). No difference in standing bouts was observed among the groups. In summary, exposure to heat stress during late gestation affects the daily time budget of pregnant heifers, especially if they are housed in pasture conditions. Insights onto heat stress effects on the daily time budget of late gestation heifers may contribute to the development of more effective management strategies to decrease the negative effects of heat exposure.

Keywords: lying time, eating time, behavioral activity.