Establishing a Yard-Specific Normal Rectal Temperature Reference Range for Horses

Abstract

Previously published equine temperature ranges often fail to state the population of animals or the method of temperature measurement used to establish the range. An inappropriate reference range can negatively affect the interpretation of measurements, resulting in animals being misdiagnosed. A yard-specific equine rectal temperature reference range was therefore calculated. A total of 652 rectal temperatures were collected from a population of 41 healthy adult horses, including a range of breeds aged 2–23 years. Rectal temperature was measured at a depth of 5 cm, using lubricated digital predictive thermometers. The normal rectal temperature range of horses on this yard was 36.0°C–38.0°C (90% confidence interval [CI] = 35.97°C–36.03°C at the lower limit and CI = 37.97°C–38.03°C at the upper limit). A Mann–Whitney test showed no significant difference between geldings and mares (Z = −1.389, P = .165). Spearman's correlation showed no significant correlations between rectal temperature and ambient temperature (Rs = 0.137, P = .052) or rectal temperature and horse height (Rs = −0.047, P = .791). The upper limit of the range is lower than most previously suggested temperature ranges, which may reflect the low-stress environment in which temperatures were measured; horses were housed in a familiar environment and examined and handled by familiar equine technicians. The findings of this study suggest that establishing yard-specific normal temperature ranges could improve early detection of fever and support biosecurity protocols in the face of infectious disease outbreaks. In addition, the results suggest that existing equine temperature ranges may need reviewing.