Pharmakologisch unterstützte manuelle Spermagewinnung und computergestützte Spermienkopfmorphometrie beim Breitmaulnashorn (Ceratotherium simum)

Pharmacologically enhanced manual semen collection and computer
assisted sperm head morphometry in the white rhinoceros
(Ceratotherium simum) In this study the influence and applicability
of pharmacologically enhanced semen collection in the white
rhinoceros (Ceratotherium simum) was investigated. Obtained semen
samples were assessed by routine methods. Additionally, computer
assisted sperm head dimensions were determined for 15 individuals
and a morphometric analysis was performed. A combination of the
alpha-2-agonist Detomidine-Hydrochloride (Domosedan) and the
partial opioid agonist Butorphanol (Butomidor) was administered
intramuscular. In order to provide adequate safety margins for the
operating persons, important requirements consist in a restraint
chute and conditioning of the rhinoceros to tolerate manipulations.
In a double blind trial, conducted on two bulls of various age and
breeding status, a strong positive influence of the
alpha-adrenergic medication was noted on both, performance and the
outcome of the manual desemination trials. The medication
facilitated manual stimulation of the genital region and semen
collection in both males, but was time consuming as repeated
collection trials had to be performed in order to obtain a single
ejaculate. Pharmacologically enhanced desemination trials with an
artificial vagina could not induce ejaculations efficiently. The
frequency of semen collection and semen quality varied considerably
between the applied desemination techniques, but also between the
rhinoceros bulls. Ejaculates collected by the pharmacologically
enhanced manual stimulation technique were incomplete, consisted of
small volumes (0,5 to 9,0 ml, with one exception of 23 ml), but
were highly concentrated in some cases (total number of sperms up
to 6,6 x 10E9 per ejaculate) and of good quality. Semen samples
collected with an artificial vagina however, were of low quality
and were contaminated by debris. Amongst other factors, the
extensive duration of the penile erection in rhinoceroses, appears
to limit the suitability of the artificial vagina for semen
collection. The determination of sperm head dimensions in the white
rhinoceros was based on a computer assisted morphometric analysis
of ejaculates from 15 individuals. The samples consisted of
pharmacologically enhanced manually collected semen and
electroejaculates. The Hamilton Thorne Morphology Analyser IVOS
(integrated visual optical system; Hamilton Thorne Research,
Beverly, USA) allowed the measurement of six metric sperm head
parameters. The sperm head dimensions found for the white
rhinoceros with a mean length of 5,4 ± 0,3 micrometers and width of
2,8 ± 0,2 micrometers (x ± SD; n=7733 analysed sperms) resemble
those of the horse as determined by the same analysis system (e.g.
UHLENBROCK 1999). A definition of morphometric criteria was
required prior to the morphometric analysis. Limit values for five
morphologic categories were calculated based on statistic
parameters (5. and 95. percentiles, minimum and maximum). The
analysis revealed a comparatively broad variation in the number of
sperm head anomalies for the 15 rhinoceroses, ranging from 4 to
16%. As to date, investigations on the relationship between
morphometry and fertility cannot be conducted in this species,
these morphometric results should be interpreted species-specific
and in conjunction with further semen parameters. In conclusion,
pharmacologically enhanced manual stimulation with an
alpha-adrenergic medication is a suitable alternative method for
repeated semen collection in the white rhinoceros, although
problems with this method as described are evident. While a
considerable variation in volume and concentration of the samples
was noted for individual rhinoceros bulls, the sperm morphology and
morphometry generally appeared homogenous.