Changes in the Quality of Rabbit Semen in 14 Consecutive Ejaculates Obtained Every 15 Minutes

Abstract

Modifications of semen quality related to ejaculation frequency is one of the most important and neglected factors from the standpoint of artificial insemination or sperm competition. New Zealand white rabbits (Oryctolagus cuniculus) offer an advantageous experimental model because they have characteristic sexual behavior, they present rapid ejaculation after a single intromission, they have a very short interval between successive ejaculations, and semen can be easily collected. The authors studied the modifications on sperm quality (semen volume, sperm concentration, sperm motility) produced by 14 consecutive ejaculations recovered every 15 min using stimulus females and an artificial vagina. Bucks were exposed every 15 min to a sexually receptive female. After each ejaculation the female was removed and reintroduced 15 min later. Sperm concentration showed a clear biphasic conduct. The amount of spermatozoa per milliliter decreased rapidly until ejaculate number 6, showed a highly significant increase in ejaculates 7-9, and decreased to nil in the last 2 ejaculates. Total number of ejaculated spermatozoa was 557 x 10(6), 76% of which were recovered from the first 4 ejaculates. Ejaculate volume also showed a biphasic conduct. In the first ejaculates the volume decreased linearly until ejaculate number 6, showed a significant increase in ejaculates 7-10, and then decreased. The total semen volume recovered during the experiment was 2.44 mL, 40% of which (0.98 mL) was recovered from the first 2 ejaculates. Individual motility in the first 6 ejaculates was preferentially progressive (60% of the sperms) and turned to random or in situ from the seventh ejaculate up. The proportion of spermatozoa with cytoplasmic droplets increased from ejaculates 6 and 7 up. The results seem to reflect an acceleration of semen transport through the epididymis when the demands for spermatozoa increase.

Analysis of sexual behaviour in male rabbits across successive tests leading to sexual exhaustion

“…Some studies have found that, after 5-6 successive ejaculations, the buck has almost no sperm in the ejaculate (Ambriz et al, 2002;Oshio et al, 1986). This finding is at odds with our behavioural data in which the ejaculatory motor pattern can exceed 43 on a given test day.…”

Semen Collection and Ejaculate Characteristics in the Indo‐Pacific Bottlenose Dolphin (Tursiops aduncus)

“…The effect of successive ejaculate collection has been investigated in a number of terrestrial species, such as horses (Squires et al, 1979; Pickett et al, 1985), bulls (Foote, 1978), dogs (England, 1999), cats (Tanaka et al, 2000), and rabbits (Ambriz et al, 2002). Comparison between results of these species and the results of this study must be made with caution because the time interval between the collection of consecutive ejaculates and the number of collection sessions per week differ.…”

Psychological and Physiological Adaptations to Sperm Competition in Humans

“…The outcome of such competition, notwithstanding mating order effects, depends on a "raffle" or "lottery" principle; that is, a particular male can increase the probability of siring a female's offspring by inseminating more sperm (Parker, 1970(Parker, , 1990. The costs of ejaculate production are nontrivial, however (Dewsbury, 1982;Nakatsuru & Kramer, 1982;Olsson, Madsen, & Shine, 1997), and repeated ejaculation can lead to sperm depletion (Ambriz et al, 2002;Preston, Stevenson, Pemberton, & Wilson, 2001). Therefore, males must trade off ejaculate production costs against the potential benefits of delivering large numbers of sperm.…”