Abstract
Average daily gain (ADG) and final test weight (FTW) were compared with libido score (L), serving capacity score (SC), reaction time to first mount (RTM), reaction time to first service (RTS) and dominance value (DV) in 90 purebred yearling beef bulls which had just completed an 140-day performance test. The bulls represented 15 breeding lines (12 Hereford, 2 Black Angus and 1 Red Angus) and nine sires within lines. Libido and serving capacity assessments were applied to randomly selected groups of two bulls which were tested for 10-minutes with nonestrous heifers restrained in service crates. RTM and RTS were recorded for both tests. Social dominance was assessed during randomized observations of social interactions between bulls within their pen groups (comprising 9 to 10 bulls) over four days. Two methods of determining social dominance (DV1 and DV2) were employed initially. Differences occurred among both lines and sire/lines in mean and best libido scores (P < .05). Sire/lines differed in L1, while both lines and sire/lines differed in L2 (P < .05). These differences were not reflected in either reaction times or serving capacity scores. Sires and sire/lines both differed in FTW (P < .05 and P < .01 respectively), while DV1 differed with sire/lines (P < .01). DV1 and DV2 were highly correlated (r = .84). Those sex-drive estimates which correlated with DV1 were the mean and best libido scores, mean serving capacity score, L2 and RTS 1 (P < .05). All correlations were negative, indicating that dominance and sex-drive may be unfavourably related in yearling beef bulls. ADG and FTW showed negative correlations with the mean and best serving capacity scores and with SC2 (P < .05). The only positive correlations between the two production traits and a sex-drive estimate was with RTM 2 (P < .05). This indicates that ADG and FTW may be unfavourably related to sex-drive in yearling beef bulls.
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