Infrared thermography in early detection of subclinical mastitis: regional temperature thresholds and environmental effects

Early detection of subclinical mastitis (SM) in dairy cows is important to minimize economic losses and improve dairy cow comfort. This study focused on the identification of threshold temperature of California mastitis test for being positive for SM and determined if it was affected by temperature-humidity index (THI). Six hundred and fifty-eight small and medium scale dairy farms were selected in four regions of Sri Lanka (UP, Up Country; MC, Mid Country; CT, Coconut Triangle; and WP, Western Province) and 4274 udder quarters were captured using thermal camera. SM positive udder quarters had a higher temperature (as mean ± standard deviation; UP, 36.4 ± 1.79 °C; MC, 36.3 ± 1.79 °C; WP, 37.7 ± 1.84 °C; and CT, 38.3 ± 1.01 °C) compared to SM negative samples. The prevalence of SM was statistically significant for udder skin surface temperature (P < 0.05) and the difference between it and flank skin temperature was statistically significant with prevalence of SM (P < 0.05). The threshold temperature differences were (in ΔT °C): UP 2.49; MC, 2.17; WP, 1.90; and CT, 1.86, and these were statistically different (B = −0.080, R = 0.957, R2 = 0.916, P < 0.05) from environmental temperature and tended to be significantly related to the THI. Thus, the threshold value of temperature difference can be applied for early detection of SM taking into consideration that threshold temperature varies with the environmental temperature and THI.