Production, Management, and the Environment

摘要

Exposure of dairy cows to heat stress negatively affects cow welfare andperformance during all the phases of the lactation cycle. Negative effectsinclude decreased milk yield, reduced immune status during the transitionperiod, and altered natural behavior. While we understand heat stressresponses in cows, one question that has yet to be answered is how lategestation heat stress affects the daily time budget of pregnant heifers. Automatedmonitoring devices (Nedap, Netherlands) were used to documentthe behavioral activity of heifers during pre- (final 60 d of gestation) andpostpartum (first 60 d of lactation) periods. Twenty-five pregnant Holsteinheifers 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 receiveda leg tag, which measured daily lying time, number of steps, andstanding bouts, and a neck tag which measured eating and ruminationtimes. Heat stressed heifers tended to spend more time eating (224 vs183 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 notdiffer. During the postpartum period, HT spent more time eating (209 vs180 min/d; P < 0.05) during wk 1 to 4 of lactation, but no differences inrumination 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 stepswas greater for HT during the postpartum period, from wk 2 to 9 (3038vs 2653 steps/d; P = 0.02). Eating frequency was similar during pre- andpostpartum (P < 0.67), however, HT had larger meals at night duringthe pre and postpartum periods compared with CL heifers. In summary,exposure to heat stress during late gestation affects the daily time budgetof first lactation heifers during both the pre and postpartum periods.Insights onto heat stress effects in heifers may contribute to the developmentof more effective management strategies to mitigate heat load.