Scrotal surface and eye area temperature are effective in identifying testicular thermoregulation and physiological changes in Nellore bulls (Bos indicus)

Bos indicus cattle is a native animal from South and Southeast Asia, regions with tropical climates. However, high environmental temperatures can compromise body and testicular thermoregulation, changing the physiological parameters, such as decreasing sperm quality. The temperature of the scrotal surface and the eye area measured by infrared thermography, has become a useful technique in the evaluation of thermoregulatory capacity and diagnosis of both testicular and physiological disorders caused by increased temperature. It is important to add new tools to evaluate the impact of environmental factors such as heat stress and its impact in reproduction. Accordingly, this study aimed to evaluate the scrotal temperature changes and the eye area temperature of Nellore bulls (Bos indicus) and its relation to physiological parameters and environmental temperature. For such, were used 12 Nellore bulls with mean of 34 ± 1.16 months of age. Evaluations were made for three non consecutive days .The scrotal surface mean temperature (SSMT, ⁰C) and eye area mean temperature (EAMT; oC) were measured by infrared thermographic camera, T620 model (FLIR Systems, USA). The images were evaluated using the FLIR Quick Report® software (FLIR Systems, USA), and were captured at a distance of 0.9 m between the camera and the scrotum. The environmental temperature (ET, oC) was verified by a data logger device (OPUS 20 THI - 8120.00, Lufft, Germany). Were also assessed rectal temperature (RT, °C) using a digital thermometer, heart rate (HR, bpm) and respiratory rate (RR; breaths/min) using a stethoscope. The data were submitted to Pearson correlation analysis using the Statistical Analysis System (SAS, 2004). The significance level was 5%. Physiological values of RT, RR and HR changed according to environmental temperature variations. The results showed a positive correlation (p<0.0001) between the ET and RT (r = 0.73), also (p = 0.0001) to ET and RR (r = 0.40), however the correlation between ET and HR showed no statistical difference (p = 0.2617). It was showed positive correlation (p<.0001) between RT and EAMT (r = 0.63). Regarding SSMT, were observed that there was positive correlation for all parameters, SSMT x ET (r = 0.87, p <0.0001); SSMT x RT (r =0.63, p <0.0001); SSMT x RR (r = 0.29, p = 0.0072); and SSMT x EAMT (r = 0.83, p = 0.0001); differently to SSMT x HR, that was found negative correlation (r = - 0.23, p = 0.03). Thus it can be consider that SSMT is affected directly by ET, RT, RR, as well as EAMT values, and it can be allow identifying the heat stress. Thus, were conclude that it is possible to evaluate the physiological changes of thermoregulation through the variation of temperature of bovine skin, in this case the mean surface of the scrotum and the eye.