Scrotal surface temperature before and after semen collection with digital infrared thermography in Nellore bulls (Bos taurus indicus)

Reproductive and economic efficiency of extensive livestock depends on bull fertility in the field, and digital infrared thermography can help to identify thermal stress in animals in a non-invasive manner. This study aimed to investigate the surface temperature of the scrotum using digital infrared thermography before and after semen collection, and to determine the correlation of these temperatures with semen quality in Nellore bulls. Semen was collected from 80 Nellore bulls via electroejaculation, and semen samples were immediate analyzed of progressive sperm motility (M) 0–100%, mass sperm motion (MM) 0–5, and sperm vigor (VIG) 0–5. The sperm morphology (minor defects, major defects and total defects) was evaluated from 200 cells with a phase-contrast optical microscopy. Digital infrared thermograms of the scrotum were obtained, before and after collection of semen, and rectal temperature (RT) was determined. Each thermogram was processed and the following data were obtained, standardizing and adopting the following nomenclature: T1: spermatic cord temperature; T2: temperature of the dorsal third of the testicles; T3: temperature of the medial third of the testicles; T4: temperature of the ventral third of the testicles, and T5: temperature of the epididymal tails. Between the anatomical points analyzed (T1 to T5) there were significantly difference (P 0.05) when compared the moments before and after electroejaculation, for the temperatures in each anatomic point. There was a correlation between RT × T1 (r=0.51; P<0.05); RT × T2 (r=0.43; P<0.05); RT × T3 (r=0.37; P<0.05); RT × T4 (r=0.33; P<0.05) and RT × T5 (r=0.32; P<0.05). There were correlations between T2 × total defects (r=0.30; P<0.05); T3 × minor defects (r=0.35; P<0.05); T3 × major defects (r=0.30; P<0.05) and T3 × total defects (r=0.42; P<0.05); T4 × minor defects (r=0.30; P<0.05), T4 × major defects (r=0.28; P<0.05) and T4 × total defects (r=0.37; P<0.05); T5 × major defects (r=0.29; P<0.05) and T5 × total defects (r=0.28; P<0.05). With these results we can see that the temperatures in the anatomical points of the scrotum will decrease in the dorsal-ventral axis, which indicates the adequate testicular thermoregulation, with difference of 4.04oC before and 3.95oC after electroejaculation. Significant positive correlations indicate that when there is an increase in rectal temperature, there is a rise in temperature of the scrotum. In the same way, the temperature of the scrotum when appears increased, there is an increase in minor, major and total defects, indicated by significant positive correlations. In conclusion, the digital infrared thermography, both before and after electroejaculation, provided accurate measurements of scrotal surface temperature and, as such, generated complementary information for seminal evaluation. Therefore, this technique is recommended for screening to detect adequate scrotal thermoregulation in the selection of breeding bulls. (CEUA/UNOESTE/Protocol#1920/2013)