Application of infrared scrotal thermography (IRST) under field conditions in bulls extensively managed in tropical Costa Rica, and its relationship with spermiogramme, clinical variables and final breeding soundness classification

Abstract

The objective of the study was to evaluate the use of scrotal surface infrared thermography in breeding soundness classification under field conditions in tropical Costa Rica. This included the usability of infrared scrotal thermography of bulls, as well as the value of the results conducted from this technique. The study was executed as a cross-sectional observational study in which a sample survey was performed. The study included 60 bulls that were clinically examined, including measurement of scrotal circumference and general health. Infrared scrotal thermography was applied and semen was collected by electro-ejaculation and evaluated by spermiogramme analysis. The repeatability of the infrared thermography method was analyzed by measuring 6 points on the scrotum repeatedly in images from the same bull. The mean repeatability of the 6 thermographic measurements was 0.96 with a high significance (p<0.0001). Additionally, the correlation between environmental temperature and the thermogram measurements was calculated using Pearsons correlation. Testicular temperature and cauda epididymal temperature were highly significant (p<0.0001) positively correlated with the environmental temperature and gradient top-bottom testicle and delta rectal- and testicular temperature were highly significant negatively (p<0.0001) correlated with the environmental temperature. The relation between the thermogram measurements and the sperm morphology (which was set as the golden standard) was analyzed using multiple linear regression analysis. Only when environmental temperature was included in the explanatory variables, environmental temperature and delta rectal and testicular temperature formed a low significant model in which 6.9% of the variation in total morphological defects can be explained by the variation in environmental temperature and delta rectal and testicular temperature.