Relationship between semen quality and pixel-intensity of testicular ultrasonograms after scrotal insulation in beef bulls

Abstract

The objective of this study was to determine the relationship between semen quality and testicular pixel-intensity derived from image analysis of ultrasonograms after scrotal insulation in bulls. In addition, the ability to predict semen quality based on testicular pixel-intensity was evaluated. Sixteen beef bulls were selected on the basis of satisfactory semen quality and normal testicular ultrasonogram appearance. Bulls were allocated into two groups for scrotal insulation for 4 days (group 1) or 8 days (group 2). Semen was collected and evaluated twice weekly and testicular ultrasonograms were evaluated once weekly for 8 weeks after removal of scrotal insulation. In general, the percentages of motile and morphologically normal spermatozoa decreased below pre-insulation levels from 1 to 5 weeks after scrotal insulation removal. Overall, group 1 had greater (P < 0.01) percentages of motile and normal spermatozoa than group 2. Mean testicular pixel-intensity (PI), and the number of pixels corresponding to the intensity that occurs most frequently (NP) decreased in the first 2-3 weeks after scrotal insulation, coincidently with the decrease in sperm motility and normal morphology. When the entire data set was evaluated, there was no association between testicular PI or NP with semen quality observed at the same week of ultrasound examinations. However, regression models indicated that testicular PI and NP accounted for 13-25% of the variation in sperm motility and morphology in ejaculates collected 2-4 weeks after ultrasound exam. Testicular PI and NP had moderate sensitivity and negative predictive values (64.5-82.6%), but low specificity and positive predictive values (33.3-61.2%) as predictors of satisfactory semen quality (> or = 60% motile spermatozoa and > or = 70% morphologically normal spermatozoa) for ejaculates collected 2-4 weeks after ultrasound exam. In conclusion, the deleterious effects of scrotal insulation on semen quality were dependent on the length of the period of insulation and were associated with changes in testicular ultrasonogram pixel-intensity. Testicular ultrasonogram pixel-intensity had a better association with future semen quality than with present semen quality and was a better predictor of unsatisfactory semen quality than satisfactory semen quality.