PREDICTING END-OF-TEST SEMEN QUALITY IN BULLS PRIOR TO PERFORMANCE TESTING

The first objective of this study was to determine if serum concentrat ions of specific hormones (testosterone, progesterone and androstenedi one) in bulls at the start of performance testing could predict semen quality at the end-of-test when used in a multivariate model. The seco nd objective was to evaluate other clinical measurements (breed, age, body weight, hip height and scrotal circumference) for predicting end- of-test semen quality. End-of-test semen quality was related to steroi d concentrations and several pre-testing measurements, including age, body weight, hip height and scrotal circumference (SC). Combining the 3 steroid concentrations into a predictive test had a sensitivity of 0 .6 and specificity of 0.5 at its most accurate point. The repeatabilit y of the test result was extremely low (r(2) = 0.16; P < 0.05). In mul tivariate analyses, breed and start-of-test SC remained significant pr edictors of end-of-test semen quality (P < 0.05) while the other varia bles were nonsignificant (P > 0.1), suggesting that start-of-test SC w as the most accurate predictor of end-of-test semen quality. Removing bulls at the start-of-test that had scrotal measurements of less than 20 cm, 24 cm, 28 cm or 32 cm resulted in sensitivities and specificiti es of 0.19, 0.94; 0.41, 0.81; 0.64, 0.56; and 0.94, 0.12, respectively . No cut-point had both adequate sensitivity and specificity. Because clinical tests were correlated, combining the tests to improve accurac y was not justified. (C) 1997 by Elsevier Science Inc.