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Effects of exposure to heat stress during late gestation on the daily time budget of nulliparous Holstein heifers.

I. M. Toledo

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06-22-2020

Abstract:

57
Effects of exposure to heat stress during late gestation on the daily time budget of nulliparous Holstein heifers.
I. M. Toledo*, V. Ouellet, B. D. Davidson, G. E. Dahl, J. Laporta. University of Florida Gainesville, FL.

Exposure of dairy cows to heat stress negatively affects cow welfare and performance during all the phases of the lactation cycle. Negative effects include decreased milk yield, reduced immune status during the transition period, and altered natural behavior. While we understand heat stress responses in cows, one question that has yet to be answered is how late gestation heat stress affects the daily time budget of pregnant heifers. Automated monitoring devices (Nedap, Netherlands) were used to document the behavioral activity of heifers during pre- (final 60 d of gestation) and postpartum (first 60 d of lactation) periods. Twenty-five pregnant Holstein heifers were housed in a freestall barns and enrolled to heat stress (HT; shade; n = 13) or cooling (CL; shade, soakers and fans; n = 12) treatments prepartum. All heifers were cooled postpartum. Heifers received a leg tag, which measured daily lying time, number of steps, and standing bouts, and a neck tag which measured eating and rumination times. Heat stressed heifers tended to spend more time eating (224 vs 183 min/d; P = 0.07) and less time ruminating (465 vs 518min/d; P = 0.05) during the prepartum period compared with CL, but DMI did not differ. During the postpartum period, HT spent more time eating (209 vs 180 min/d; P < 0.05) during wk 1 to 4 of lactation, but no differences in rumination was observed (P = 0.85). Lying time was reduced (P = 0.01) by 59 and 88 min during weeks −7 and −6 prepartum and 84 and 50 min (P = 0.05) during wk 2 and 3 postpartum in HT. The number of steps was greater for HT during the postpartum period, from wk 2 to 9 (3038 vs 2653 steps/d; P = 0.02). Eating frequency was similar during pre- and postpartum (P < 0.67), however, HT had larger meals at night during the pre and postpartum periods compared with CL heifers. In summary, exposure to heat stress during late gestation affects the daily time budget of first lactation heifers during both the pre and postpartum periods. Insights onto heat stress effects in heifers may contribute to the development of more effective management strategies to mitigate heat load.

Keywords: heat stress, late gestation, behavioral activity.