Infrared thermography and Doppler ultrasonography reveal divergent scrotal thermoregulation strategies in Nelore and composite (5/8 Charolais × 3/8 Bos indicus) beef bulls.

The present study aims to compare the testicular development and the capacity to maintain homeothermy and scrotal thermoregulation of young Nelore and Canchim (5/8 Charolais × 3/8 Bos indicus) bulls raised in the tropics, using infrared thermography and color Doppler ultrasonography. Forty-eight young bulls (24 Nelore and 24 Canchim) were raised using an intensive rotational grazing system (Urochloa brizantha, cv. BRS Piatã). The bulls had free access to shade and rotated between paddocks every seven days, with the pastures resting for thirty-five days. Over 12 consecutive months, the bulls were evaluated using calipers, clinical thermometers, infrared thermography, and color Doppler ultrasonography. Data were analyzed for the main effect of breed (Nelore and Canchim) and animal age (8 to 19 months), and the possible breed × age interaction. Nelore demonstrated greater (P < 0.05) competence in maintaining systemic homeothermy than Canchim. The epididymal tail temperature was higher (P < 0.05) in Nelore bulls (32.8 ± 0.1 °C) compared to Canchim (32.0 ± 0.1 °C). At the end of the experiment, Nelore bulls showed a smaller (P < 0.05) color Doppler area in the pampiniform plexus (1173.3 ± 106.1 mm2) compared to Canchim (1763.7 ± 138.1 mm2). Our study used a combination of infrared thermography and color Doppler ultrasonography to assess scrotal temperature and hemodynamics. This approach could contribute to the development of initial reference parameters, which are an important tool for understanding adaptability issues.