Reproductive characteristics of bulls from two breed compositions and their correlations with infrared thermography.

The objective was to evaluate reproductive characteristics of crossbred Girolando (Gyr x Holstein) bulls from two breed compositions and correlate these results with infrared thermography data. Evaluations were performed considering sperm motility, vigor and morphology; scrotal circumference; body morphology and temperament. Infrared thermography was performed to determine surface temperatures of ocular and scrotal areas. Thermoregulation capacity was assessed by differences between air and rectal temperatures, air and maximum temperatures in ocular and scrotal areas, and dorsal and ventral lines of the scrotum. Data analysis was performed using a linear mixed model (breed composition as fixed effect and year of evaluation as random effect). Spearman correlation coefficient was used to associate thermography and reproductive data. Girolando 3/4 Holstein bulls had higher (P ≤ 0.001) scrotal circumference and higher average body morphology and temperament, whereas 5/8 Holstein bulls had a higher (P < 0.001) percentage of major-type and total sperm defects. Girolando 3/4 Holstein bulls had scrotal temperatures 0.8 °C higher (P < 0.001) and 5/8 Holstein bulls had 9.8% and 10.6% higher differences on "rectal - scrotal area" and "ocular area - scrotal area" temperatures, respectively. Ocular area temperatures had negative correlations (P ≤ 0.1) with sperm motility and vigor, and positive correlations (P < 0.001) with minor-type and total sperm defects. Ventral line scrotal temperatures had positive correlations (P < 0.001) with minor-type and total sperm defects. Girolando 3/4 Holstein bulls were found to be superior to 5/8 Holstein bulls for reproductive characteristics. Under non-stressing climatic conditions, semen characteristics of Girolando bulls were more influenced by breed composition than by the capacity for scrotal thermoregulation. Correlations between semen quality and scrotal temperatures can aid in the identification of bulls for breeding, particularly when a large number of animals are in the tests.