Scrotal surface mean temperature differ throughout the day in Nellore bulls (Bos indicus)

The Nellore cattle are characterized, in general, like animals more adapted to tropical environments. Meanwhile, environmental high temperatures may cause elevation of testicular temperature harming sperm quality. Scrotal superficies mean temperature (SSMT) measured by infrared thermography camera has been became a useful technology in assessment of thermoregulatory capacity and the diagnosis of testicular disorders caused by increased temperature. However, few studies demonstrated variation of SSMT throughout the day. Thus, the aim of this study was to evaluate scrotal temperature changes of Nellore bulls (Bos indicus) during different periods of day (morning and afternoon) and, their relationship with their physiological parameters and environmental temperature. For this, twelve Nellore bulls were used with 34±1.16 months of age. The assessments were made during three nonconsecutive days evaluating on the morning (7 a.m.) and afternoon (12 p.m.). The SSMT (oC) was measured using an infrared thermography camera, T620 model (FLIR Systems, USA). The images were evaluated using the FLIR Quick Report® software (FLIR Systems, USA) and captured from a distance of 0.9 m between the camera and the scrotum. The environmental temperature (ET) was measured by Data Logger (OPUS 20 THI - 8120.00, Lufft, Germane). It was also evaluated the rectal temperature (RT, °C) by a digital thermometer; heart rate (HR; bpm); and respiratory rate (RR; breaths/min) using a stethoscope. Data were submitted to analysis of variance using the MIXED procedure of Statical Analysis System (SAS, 2004). Significance difference was considered when P≤0.05. SSMT measured on the morning (28.76±0.19oC) presented lower (P<0.0001) than SSMT measured on the afternoon (32.70±0.12oC). In the same way, on the morning ET (13.91±0.29oC), RT (37.02±0.12oC) and RR (24.02±1.02 breaths/min) were lesser (P<0.0001) than on the afternoon (ET = 25.58±0.3oC; RT = 38.46±0.07oC; RR = 30.09±1.20 breaths/min). However, there was no difference in heart rate (P=0.19) measured on the morning (79.95±2.47 bpm) and on the afternoon (75.58±2.62 bpm). Considering the previous results during the studied periods, morning and afternoon, respectively, of RR (24.02±1.02; 30.09±1.20 breaths/min) and HR (79.95±2.47; 75.58±2.62 bpm) were observed the influence of environmental temperature on RR and HR values obtained during both periods according to normal parameters suggested to Nellore bulls during winter (33.6±0.67 breaths/min and 68.9±0.80 bpm). Knowing that, for spermatogenesis normally occurs, the testicles temperature must be between 2 and 6°C lower than body temperature and the environmental temperature should be between 27 and 32oC, were noted that, there is a difference of more than 6°C between SSMT (28.76±0.19oC) and body temperature (37.02±0.12oC), and a noticeable decrease in environmental temperature during the morning (13.91±0.29oC). Subsequently, during the afternoon, the SSMT values, RT and ET were significantly different, and, still were kept within normal parameters. About the differences in the values of SSMT during the two periods of the day, in the morning (28.76±0.19oC) and afternoon (32.70±0.12oC), we can conclude that the SSMT varies according the temperature of the day, indicating that it is precise to standardize the period in which the assessment is made and thus minimize variations caused by environment temperature on the day. In this manner, these results can contribute attempts to establish selection criteria of the reproductive capacity of animals.