Infrared Thermography and Testicular Morphometry in Rams of Different Breeds: Implications for Reproductive Fitness in Tropical Environments

Abstract

The Brazilian sheep industry relies on extensive production systems, where rams are frequently exposed to high ambient temperatures and low relative humidity, potentially compromising reproductive efficiency. Testicular thermoregulation is critical for spermatogenesis, requiring scrotal temperature to be 2˚C-6˚C below core body temperature. This study aimed to evaluate testicular shape and infrared thermography (IRT) in 38 rams from four different breeds (Poll Dorset, Dorper, Santa Inês, and Suffolk) managed under tropical extensive conditions in Botucatu, Brazil. Testicular morphometry (scrotal circumference—SC, width, length, volume) and IRT of scrotal regions (dorsal, medial, ventral), as well as rectal, eye, and nose temperatures, were assessed. Significant differences were found in SC among breeds (P = 0.024), with Dorper rams having larger SC. IRT revealed significant variations in the ventral temperature of the right testicle (P = 0.039), dorsal temperature of the left testicle (P = 0.006), and mean dorsal temperature of both testicles (P = 0.025). Poll Dorset, a wooled breed, exhibited higher mean dorsal testicular temperatures, consistent with wool’s insulating effect hindering heat dissipation. Conversely, Suffolk rams, despite being wooled, showed lower dorsal testicular temperatures, suggesting complex breed-specific thermoregulatory mechanisms or anatomical adaptations. Dorper rams (hair, white-coated) showed lower ventral scrotal temperatures, indicating better heat dissipation. Nose temperature also varied significantly (P < 0.001), reinforcing breed-specific thermal regulation. These findings underscore the influence of breed characteristics, particularly coat type and color, on testicular thermoregulation and overall heat management in rams, providing valuable insights for selecting resilient breeding stock in challenging tropical environments.