Validation of Indwelling Vaginal Sensor to Monitor Body Temperature in Ewes

Remote-sensing technology facilitates longitudinal collection of body temperature during periods of hot or cold environmental stress without human interference, producing high-frequency measurements whilst reducing labour and stress to the animal. A pilot study was conducted to validate an improved, minimally invasive method for the continual measurement of vaginal temperature (VT) in female sheep. A silicon mould of a modified controlled internal drug release (CIDR) device (Zoetis Animal Health, Parsippany), was manufactured to securely house a temperature logger (Micro-T 16-bit; Star Oddi, Iceland) and allow direct contact at the collection site. These temperature-sensing CIDR devices were validated against manual rectal temperature (RT) measurements collected from 15 mature, non-pregnant, non-lactating Merino ewes. Rectal temperature was measured from each individual, six times per day in 2-h intervals for 14 consecutive days. The simultaneous measures of VT and RT did not differ significantly within each ewe (P > 0.05) and demonstrated a moderate linear relationship (R2 = 0.62, P < 0.05). The mean (± SEM) difference between RT and VT was small (0.010 ± 0.004 °C), with a 95% confidence interval of − 0.26 to 0.29 °C. Additionally, the coefficient of variation was lower on average for VT (0.49%) compared to RT (0.59%). Differences among paired readings were likely due to interval variation as well as penetration depth, air influx and faecal temperature when collecting RT. The initial silicone manufacturing costs were high (2200 AUD), with each unit costing 1.25 (AUD) thereafter; however, the temperature-sensing CIDR device was an effective and efficient research tool for the remote monitoring of body temperature. While further validation of these devices within extensive grazing environments is warranted, the collection and analysis of longitudinal physiological data from ewes has the potential to improve a variety of management aspects related to extensively grazed ewes maintained and joined in harsh conditions.