Spermatozoa Morphology during the Breeding Season in Thoroughbred Stallions in Japan

Abstract

ABSTRACT. The morphology of spermatozoa of modern Thoroughbred stallions in Japan was investigated during the breeding season. A total of 299 semen samples were collected from the penises of 16 stallions immediately after service. The rate of abnormalities in sperm heads and tails, spermatozoa with cytoplasmic droplets and slides with medusa cells to total observed slides in each stallion were 3.9 ± 2.1%, 11.5 ± 5.9%, 2.4 ± 2.6% and 20.1%, respectively. The values for the area, length, width and aspect ratio of the stallion sperm head were 12.54 ± The breeding stallion for Thoroughbred racehorses is prized for the chance of siring future champions. The number and quality of his prodigy depend, however, on the quality of his spermatozoa. Morphological features of the spermatozoa provide useful criterion for assessing the quality of semen and clinical value for informing veterinary decisions [6]. Jasko et al. reported that the rate of spermatozoa with normal morphology correlates positively with the rate of fertility [16]. Wide variation in the size and shape of spermatozoa occurs in virtually all mammalian species, however, and an abundance of abnormalities can be found. The sperm head has been reported to be larger in semen taken from subfertile stallions than in that from fertile stallions [6,14]. The converse has also been reported [17], and variations in size of the sperm head have been attributed to the staining methods of the studies [4,5,15,22]. The staining method has also influenced the ratio of morphologically abnormal spermatozoa to the total sperm count [18,21]. These problems remain unsolved.For a popular stallion, the number of services may exceed 200 in a single breeding season. A previous study showed in Thoroughbreds engaged in five services every hour that, in spite of decreases in volume, number or concentration of spermatozoa, sperm viability was not different in the ejaculation repeats [23].The morphology of the spermatozoa has not been investigated in Thoroughbred stallions during the breeding season in Japan. We hypothesized that if the ejaculated semen could be examined from time to time throughout the breeding season, the semen would exhibit morphological differences and allow clarification of abnormalities in the spermatozoa produced during that critical period in the work of the stallions. Morphological data on semen ejaculated throughout the breeding season would provide a reference index for judging the normal morphology of spermatozoa to estimate reproductive activity at copulation. To clarify the morphology of spermatozoa from Thoroughbred stallions servicing a large number of mares during the breeding season, in the present study we examined spermatozoa collected from the semen remaining in the urethra of the penis immediately after the stallion dismounted from servicing since sperm head measurements from dismount semen are representative of those of the ejaculate [13].The study was comprised 16 Thoroughbred stallions in Hokkaido within age range of 4 to 15 (mean ± SD, 8.9 ± 3.2) y...

Change in Morphology of Spermatozoa from Dismount Semen during the Breeding Season in Thoroughbred Stallions in Japan

“…The morphology of equine spermatozoa has been reported to reflect the quality [6,7,8, 14, 18,19,20]. Jasko et al .…”

“…Differences in sperm morphology have been reported between the four seasons of the year [7, 16], but little is known about the changes in sperm morphology throughout the breeding season itself. In Thoroughbred stallions in Japan, we previously found that the morphology of the sperm head varies during the breeding season [14]. …”