Effects of ambient temperature and relative humidity and measurement site on the cow’s body temperature measured by infrared thermography

We assessed the effects of ambient temperature and relative humidity on the infrared thermography (IRT) temperature of dairy cows, and evaluated the IRT body surface temperatures as effective surrogates of cow’s rectal temperature. The rectal temperature and the IRT temperatures (eyes, nose, skin) of 171 cows were measured and obtained at the ambient temperatures of －1 to 36 ℃. The standard deviations of IRT temperatures decreased with the rising of ambient temperatures. Both ambient temperature and relative humidity had significant impact on the IRT temperatures (P＜0.000 1). The effect of relative humidity on the IRT temperatures was less than that of ambient temperature. Regression analysis showed that significant correlation existed between the rectal temperature and the IRT temperatures of eyes, nose and skin (P＜0.000 1), with R² being 0.494 0, 0.328 0, and 0.273 1 and the standard errors being 0.17, 0.19, and 0.20 ℃, respectively. The correlation was improved notably by breaking down the ambient temperature (T) into three segments, i.e., T≤10 ℃, 10 ℃＜T≤26 ℃, T＞26 ℃. Linear regression based on the segmented ambient temperature outperformed the original univariate linear correlation. Therefore, the influence of ambient temperature on the IRT temperatures cannot be ignored, and the IRT temperatures can accurately predict the body temperature using the segmented ambient temperature. Although all IRT temperatures (eyes, nose, and skin) could indicate the cow’s body (rectal) temperature, the IRT temperature of eyes is preferred because it is simple to measure, least affected by the ambient temperature, and has the highest accuracy.