Non-invasive heat stress assessment in Murrah buffalo, crossbred (Bos taurus × Bos indicus) cattle and Vechur cattle using inner canthus infrared thermography.

Heat stress is a critical challenge affecting livestock productivity and welfare, particularly in tropical climates. Infrared thermography (IRT) has emerged as a non-invasive tool for assessing physiological responses to heat stress. The study aimed to evaluate the heat stress responses in Murrah buffaloes, crossbred cattle, and Vechur cattle using inner canthus infrared thermography as a non-invasive tool under farm conditions in Kerala, India. The experiment was conducted at the Silent Valley Farm Platform, Kerala state, India during February-May 2023, a period of peak thermal stress for dairy animals. Eighteen calves (6-12 months old) were equally assigned to three groups representing each breed/species. Each group consisted of an equal number of male and female calves (three males and three females). Physiological responses (respiratory rate, heart rate using a polar monitor) were assessed in the morning (8:00 AM) and afternoon (2:00 PM). Surface temperatures of inner canthus were captured using an infrared camera (testo 865). The statistical analysis revealed significant differences in heart and respiratory rates between breeds, with crossbred calves exhibiting the highest respiration rate. Breed significantly impacted inner canthus temperatures, highlighting the varying influence of physiological and environmental factors on different breeds. Crossbred calves consistently exhibited the significantly (p < 0.001) highest inner canthus temperature compared to Murrah buffalo and Vechur cattle, both in the morning and afternoon. Murrah buffaloes showed intermediate temperatures, while Vechur cattle had the lowest inner canthus temperatures. The inner canthus surface temperature showed strong positive correlations with respiratory rate and thermal indices, including afternoon THI (r = 0.725, p < 0.001) and average daily THI, indicating its significant role as an indicator of heat stress in livestock. In conclusion, inner canthus infrared thermography effectively differentiated breed-specific thermal responses, supporting its utility as a reliable and non-invasive tool for assessing heat stress in tropical dairy production systems.