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Effect of episodic heat stress on behavior, body temperature, and lameness of lactating dairy cows on farms in northern New York.

C. S. Ballard

Events

06-23-2020

Abstract:

260
Effect of episodic heat stress on behavior, body temperature, and lameness of lactating dairy cows on farms in northern New York.
C. S. Ballard*, S. Green, S. Baldwin, A. E. Pape, R. J. Grant. William H. Miner Agricultural Research Institute Chazy, NY.

To assess the impact of episodic heat stress on lameness, resting time and body temperature of dairy cattle on farms in northern New York with varying degrees of heat abatement, a study was conducted from June through September 2019 on 4 Holstein herds. Farm A was a sand-bedded freestall with no mechanical ventilation in housing area. Farm B was a sand-bedded freestall with fans over stall beds. Farm C was a freestall, sawdust/mattress with fans/misters over feedbunk and stall beds. Farm D was a freestall, sawdust/mattress with fans over stall beds. Thirty cows with lameness score ≤2 served as a focal group averaging over 45.4 kg/d on each farm. Temperature and relative humidity were recorded continuously and temperature humidity index (THI) was calculated every 10 min. Wind speed (m/s) was measured weekly at standing and lying positions throughout pens. Lameness was scored at beginning and end of study. Lying behavior (h/d) and body temperature (reticular, �C) were measured continuously. Lameness (not lame vs. lame) from beginning to end of study was analyzed by Chi-squared analysis using Freq procedure (SAS 9.4). Retrospectively, 6 d of cool weather (mean THI <65, COOL) and 6 d of hot weather (mean THI ≥75, HOT) were selected and lying behavior and reticular temperature (RT, �C) data were analyzed by farm using Mixed procedure (SAS 9.4). All farms except Farm B increased lameness (P < 0.05) from beginning to end of summer. While all farms were impacted by heat stress (P < 0.01), Farm A was impacted the greatest with 21.4% decrease in lying time and 0.9�C increase in RT on HOT days. Farm B and C were impacted the least with 10.8% and 12.5% decrease in lying time and 0.4�C and 0.3�C increase in RT on HOT days, respectively. The wind speed on Farm A averaged 0.3 m/sec throughout the pen with least air flow in stall beds. Farms B and C had greater air flow in stall beds at resting level (1.0 and 0.9 m/sec, respectively) which likely resulted in less impact on lying time of cows during heat events compared with Farms A and D. Cows on all farms were impacted by episodic heat events to varying degrees with the cows without additional mechanical ventilation being impacted the greatest.

Keywords: heat stress, lying time, body temperature.