Assessing sex-drive in young Bos taurus bulls

Objectives in this study were to determine the accuracy of different method s of evaluating libido score (L), service rate (SR) and reaction time to se rvice (RTS) in yearling Bos taurus bulls. Using restrained, non-estrus fema les, 26 yearling Bos taurus bulls were evaluated a total of eight times (fo ur sessions, two tests per session) over 2 consecutive months for L, SR, an d RTS. Individual bull variation influenced both L (P < 0.0001) and SR (P < 0.003). Repeatability was moderate for L (R = 0.64) and low for both SR (R = 0.12) and RTS (R = 0.04). Under the conditions of this study and charact eristics of these tests, variance was reduced to 69-73% for L and 26-23% fo r SR with four to eight repetitions, respectively. Bulls that scored highly in the first session, however, tended to score highly throughout. Although , three bulls did not serve in any test, RTS was independent of effects. Ho wever, the tendency of RTS to decrease, and for L and SR to both increase w ith consecutive tests, suggests influences other than genetic, such as lear ning and/or environmental factors. These tendencies were most evident in bu lls which obtained low L scores at the first session. It was concluded that , despite the important degree of individual variability observed in L and SR, accurate quantitative evaluation of the sex-drive in young Bos taurus b eef bulls would benefit from use of test procedures of greater repeatabilit y. (C) 2001 Elsevier Science B.V. All rights reserved.