title: Effects of weather variables on thermoregulation of calves during periods of extreme heat.
abstract: OBJECTIVE
  To determine effects of ambient temperature, relative humidity, wind speed, relative barometric pressure, and temperature-humidity index (THI) on nasal submucosal and rectal temperatures in cattle during extreme summer conditions.
  
  
  METHODS
  20 black crossbred beef heifers (mean body weight, 217.8 kg).
  
  
  METHODS
  Nasal submucosal and rectal temperatures were monitored every 2 hours for 24 hours on 3 nonconsecutive days when ambient temperature was forecasted to exceed 32.2°C. Ambient temperature, relative humidity, wind speed, and relative barometric pressure were continuously monitored at a remote weather station located at the research facility. The THI was calculated and used in the livestock weather safety index (LWSI). Relationships between nasal submucosal or rectal temperature and weather variables were evaluated.
  
  
  RESULTS
  Nasal submucosal and rectal temperatures were related to all weather variables monitored. A positive relationship was determined for ambient temperature and THI with both nasal submucosal and rectal temperatures. A negative relationship was evident for nasal submucosal and rectal temperature with relative humidity, wind speed, and relative barometric pressure. Nasal submucosal and rectal temperatures increased with increasing severity of LWSI category.
  
  
  CONCLUSIONS
  Effects of environmental conditions on thermoregulation in calves exposed to extreme heat were detected. The positive relationship between nasal submucosal temperature and ambient temperature and THI raised concerns about the efficacy of intranasal administration of temperature-sensitive modified-live virus vaccines during periods of extreme heat. Environmental conditions must be considered when rectal temperature is used as a diagnostic tool for identifying morbid cattle.
authors.affiliation: Department of Diagnostic Medicine and Pathobiology, College of Veterinary Medicine, Kansas State University, Manhattan, KS 66506.
authors.forename: Miles E
authors.initials: ME
authors.lastname: Theurer
authors.forename: David E
authors.initials: DE
authors.lastname: Anderson
authors.forename: Brad J
authors.initials: BJ
authors.lastname: White
authors.forename: Matt D
authors.initials: MD
authors.lastname: Miesner
authors.forename: Robert L
authors.initials: RL
authors.lastname: Larson
mesh_terms: D000818:Animals; D001833:Body Temperature Regulation / Q000502:physiology*; D002417:Cattle / Q000502:physiology*; D055874:Extreme Heat; D005260:Female; D006813:Humidity; D012621:Seasons; D013997:Time Factors; D014887:Weather; D014919:Wind