The impact of heat stress on the fertility of the Australian Merino is of great interest following the reported increase in global ambient temperatures and anecdotal decline in fertility rates following artificial reproductive technologies. Yet, the fluctuations in core body temp which occur during the ewes’ oestrous cycle remain to be fully elucidated, as does the influence of exogenous hormones and sedatives which are necessary for artificial insemination (AI). As such, the core body temperature (Tb) of Merino ewes was investigated using novel intravaginal temperature data loggers following oestrous synchronisation and sham AI. Experiment 1 compared the core body temperature of ewes in a natural oestrus with those that had been synchronised for oestrus (progesterone pessary inserted for 14 days + 400 IU pregnant mare serum gonadotrophin at pessary removal). Experiment 2 observed whether sedation (Xylazine, Acepromazine-Ketamine-Lignocaine or saline) prior to sham AI affected ewe core body temperature. In experiment 1, although the magnitude of difference was small, ewes which were synchronised recorded a higher mean Tb (39.28±0.05) then those undergoing a natural oestrus (39.22±0.05; p<0.05). In experiment 2, both sedatives increased Tb in comparison to the control (p<0.05). Xylazine produced the highest maximum temperature (39.97±0.15) with its effect on Tb over time shown to be immediate albeit short lived. The temperature increase resulting from Acepromazine-Ketamine-Lignocaine (39.89±0.11) regime was slow in onset but produced a prolonged elevation in Tb when compared to xylazine, suggesting lasting effects beyond the day of AI. Overall, these findings indicate that oestrus synchrony and sedation alter the ability of ewes to thermoregulate, however further studies are needed to determine the biological significance of this increase in core body temperature on fertility when ewes are exposed to heat stress inducing conditions.