Study of copulatory behaviour in old male rabbits

Male rabbit sexual behaviour consists of a single mount followed immediately by ejaculation. In young bucks this pattern changes gradually as they reach sexual satiety in a day and sexual exhaustion after several daily tests. Little is known about the characteristics of sexual behaviour in old rabbits (aged 48-54 mo) within a day and across daily tests leading to sexual exhaustion. By using sexually receptive (young) females, changed within a session to maximise copulation, we found that: a) the inter-ejaculatory interval increased between the first and last days of testing; b) test duration was 3.1 h on day 1 and 0.5 h on day 15; c) the “miss rate” (i.e., mounts not accompanied by ejaculation) significantly increased from the first to the last day of testing, regardless of when this occurred in each individual buck; d) the total number of ejaculations displayed in a session significantly decreased between the first and the last day of testing in all males; e) scent-marking (“chinning”) frequency significantly decreased after copulation to satiety, relative to that quantified at baseline, and was restored the following day. Compared with young bucks our results indicate quantitative, rather than qualitative, differences in sexual behaviour associated with age in rabbits. Specifically, on day 1 old bucks spent a shorter time engaged in copulation and displayed a lower number of ejaculations before reaching satiety than young males. In contrast, the interval between ejaculatory events and the “miss rate” increased across test days in both old and young rabbits. These results merit investigating the neuroendocrine mechanisms underlying the display of such an active sexual behaviour by old rabbit bucks.