Background: Peri-anaesthetic hypothermia is a well-documented complication of general anaesthesia and is associated with prolonged recovery, impaired wound healing, and delayed coagulation. Fluid warmers can be used to mitigate heat loss, but there is little evidence supporting their effectiveness in equine anaesthesia. Objectives: To determine whether administration of warmed intravenous fluids attenuates heat loss during general anaesthesia in horses. Study design: Prospective, randomized, crossover study. Methods: Six healthy adult horses were anesthetized twice and administered intravenous fluids with the HOTLINE (R) Blood and Fluid Warmer either activated or inactivated. Core body temperature was recorded at four anatomic sites (rectum, nasopharynx, pulmonary artery, and urinary bladder), and fluid temperature was measured in the fluid bag, proximal to the warmer, and distal to the warmer. Linear mixed-effects models evaluated the effects of warmer status, time, measurement site, and ambient temperature, including relevant interactions, with random intercepts for horse. Results: Overall core body temperature differed statistically but not clinically meaningfully between warmer conditions; however, warmed fluid administration significantly reduced the rate of temperature decline (time × warmer interaction, β = 0.0033°C/min, SE = 0.001, p = 0.0004). Fluid temperature distal to the warmer increased substantially with warmer activation, and ambient temperature strongly influenced fluid temperature (χ 2 = 634.2, p < 0.0001). Main limitations: Small sample size; environmental variability; no surgical procedure. Conclusions: Although warmed intravenous fluids did not increase core temperature, they significantly attenuated intra-anaesthetic heat loss. The HOTLINE (R) Blood and Fluid Warmer increased delivered fluid temperature and provided a modest but measurable protective effect against hypothermia. These findings are the first to demonstrate that warmed fluid administration can slow heat loss in horses under general anaesthesia.