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A yearlong study: Effects of weather and animal characteristics on respiration rate in dairy cattle.

G. Tresoldi

Events

06-23-2020

Abstract:

258
A yearlong study: Effects of weather and animal characteristics on respiration rate in dairy cattle.
G. Tresoldi*1,2, M. Hejazi1, C. B. Tucker2. 1College of Agriculture, California State University Chico, CA, 2Center for Animal Welfare, Department of Animal Science, University of California Davis, CA.

Respiration rate (RR) is often used to assess heat stress in cattle at earlier stages. However, it is unclear which RR thresholds indicate that cattle are hot. Throughout a year, we recorded weather variables and RR of 406 females (newborns to 6th lactation cows) totaling 11,210 records. Our goal was to determine which weather variable or thermal index best predicted RR and to evaluate how individual animal characteristics (e.g., animal type, breed, posture and location within pen) affected RR outcomes. Preliminary data analysis was done using mixed models, linear and logistic regression. In this study, RR ranged from 16 to 184 breaths/min. Air temperature (AT) alone best predicted RR among the 21 parameters tested. It accounted for 35% of the observed RR variation. During observations, AT ranged from 1.8 to 43.9�C. Our findings suggest that RR < 40 breaths/min, a threshold often considered the upper normal limit in veterinary textbooks, were unlikely. At 25�C, for example, only 1 in every 10 cows were estimated to have RR < 40 breaths/min. This AT is normally referred to as within the cow's thermoneutral zone. Overall, every 10�C increase in AT resulted in +14 breaths/min. Among animal type categories, calves were the most vulnerable, while dry cows were the least sensitive group (+17 and +11 breaths/min every 10�C, respectively, P < 0.01). Jersey animals were also more sensitive than Holsteins (P = 0.02), but the biological significance of the difference is unclear (+3 breaths/min every 10�C). RR were the lowest when lactating cows were near the feed bunk in comparison to other areas (46 vs. 53 breaths/min, respectively, P < 0.01). The latter can likely be attributed to the presence of soakers at the feedline. Finally, posture did not affect RR outcomes (lying vs. standing = 50 vs. 51 breaths/min; P = 0.17). In a Mediterranean climate, AT was the most reliable predictor of RR in dairy cattle. However, characteristics such as animal type, breed and location within pen should be taken into consideration when making decisions about heat load management. These decisions have important implications for the effectiveness of heat abatement strategies.

Keywords: heat stress, welfare, physiology.