Rumen temperature is a reliable proxy of core body temperature in sheep (

Abstract

Context In ruminant animals, such as sheep, the maintenance of a stable core body temperature is achieved through the controlled process of thermoregulation. The live export of sheep from Australia can expose sheep to heat stress, especially when vessels near, or cross, the equator, that can impact on animal welfare by causing hyperthermia. Aim The use of thermologgers located in the rumen of sheep could provide a direct, real-time method to monitor the thermal status of sheep during live export without the need to handle animals during shipping. We determined the relationship between core temperature and rumen temperature during changes in various factors that impact on an animal’s heat balance. Methods Sixteen wethers were implanted with thermologgers in the rumen to measure rumen temperature and in the abdominal cavity to measure core temperature. The sheep were exposed to environmental conditions similar to those experienced by sheep on live export vessels. The environment was assessed using the wet-bulb temperature. In the first trial, eight Merinos were shorn while the remaining eight retained their fleece. In the second trial all sheep were shorn, and eight sheep were offered a chaff diet and eight a pelletised diet while the wet bulb temperature increased. The rumen and core temperatures were compared. Key results We show that when core temperature increased during exposure to heat load, so did rumen temperature and, despite relatively large changes in overall body temperature, the difference between these temperatures remained stable. The daily average relationship between rumen and core temperatures was 0.5 ± 0.1°C and that difference was not affected by water ingestion, length of fleece, diet composition, or exposure to hot and humid conditions similar to those reported on live export vessels. Conclusion and implications By subtraction of 0.5°C from the measured rumen temperature in live export sheep, the use of rumen thermologgers would provide a reliable measure of core temperature and hence an indication of the thermal status of the sheep throughout the export journey.