The change in rumen temperature post-drink can be used to estimate water intake in sheep.

In ruminants, water ingestion causes an immediate and measurable decline in rumen temperature. While this physiological response is well established, its application for estimating water intake has not previously been investigated. This study assessed the suitability of a thermodynamic modelling approach to estimate water intake in sheep using intra-ruminal temperature data. A fluid calorimetry equation was first validated under controlled laboratory conditions, then applied to data from six sheep fitted with intra-ruminal temperature loggers. Animals were offered water of known volume and temperature, and intake estimations were calculated using the temperature drop, baseline rumen temperature, water temperature, and estimated rumen volume based on liveweight. To improve volume estimation, additional rumen volume and liveweight data from a separate group were used to generate a generalised prediction equation for rumen volume. The approach underestimated the volume of water consumed, and so we developed a correction factor to account for physiological variation in the effective rumen volume at the time of drinking. Using the effective rumen volume in calculations resulted in estimated intake volumes that generally aligned with the measured values (P < 0.01). Our results demonstrate that measured changes in intra-ruminal temperature can be used to estimate water intake, offering a promising tool for precision livestock monitoring in extensive grazing systems.