| Summary: | 碩士 === 國立中興大學 === 畜產學系 === 91 === Seasonal Changes of Semen Characteristics in Dairy Goat Bucks
Shao-Chih Chang
Abstract
The purpose of this study was to investigate the effect of photoperiod and season on fresh semen characteristics and frozen semen quality of dairy goat bucks. Seven healthy and sexually matured dairy goat bucks were used in this study. Scrotal circumference were measured and semen samples were collected with an artificial vagina once weekly during a year. Semen volume, mass activity score and motility score of sperm, percentage of abnormal sperm and dead sperm, sperm concentration and total sperms per ejaculation were measured respectively. Semen with 3.0 or higher score of mass activity of sperm were diluted with 10％ skim milk extender biweekly and cryopreserved for one week and three months respectively. Afterward, the post-thawed motility score and viability of sperm in frozen semen were evaluated. The natural photoperiod was divided into long-daylight period（＞12 hrs）and short-daylight period（＜12 hrs）groups, and the year was divided into：spring, summer, autumn and winter seasons. The result showed that the percentage of abnormal sperm（7.18±0.28 vs.5.81± 0.26％）, sperm concentration（4.11±0.07 vs.3.65±0.06 ×109 sperms/ml）and total sperms per ejaculation（4.67±0.09 vs.4.16±0.10 ×109 sperms）of long-daylight period group were higher than those in short-daylight period group（P＜0.05）.There were no significant difference（P＞0.05）in scrotal circumference, semen volume, mass activity score and motility score of sperm and the percentage of dead sperm between two photoperiods groups.
The maximal scrotal circumference of dairy goat bucks occurred in autumn（30.27±0.08 cm）and was significantly higher than those in other seasons（P＜0.05）. Semen volume was higher in autumn（1.30±0.03 ml）, lower in spring（1.03±0.02ml）and it showed significantly seasonal difference
（P＜0.05）. The mass activity and motility score of sperms in spring
（3.90±0.07 and 2.87±0.07）were significantly lower than those in the other seasons（P＜0.05）. The highest percentage of dead sperms presented in spring
（25.54±1.41％）and it was significantly higher than those in the summer
（21.10±0.64％）and winter（21.12±1.10％），but there were no significantly difference between spring and autumn（P＞0.05）. The percentage of abnormal sperms was highest in the autumn and lowest in the winter. Sperm concentration in winter（3.46±0.06×109 sperm/ml）was significantly lower than those in other seasons（P＜0.05）. Total sperms per ejaculation in summer
（4.76±0.12×109 sperms）and autumn（4.77±0.12×109 sperms）were significantly higher than those in the spring（4.18±0.09×109 sperms） and winter（3.93±0.14×109 sperms）（P＜0.05）。
Post-thawed motility score of sperm in frozen semen cryopreservated for one week was significantly higher in short-daylight period group（2.07±0.25）than those in long-daylight period group（1.83±0.0l）（P＜0.05）,and it was lower in spring（1.67±0.05）than those in other seasons. There were no significantly difference in viability of sperms between two daylight period groups and between seasons. Semen cryopreservated for three months showed significant difference on post-thawed motility score of sperms between different daylight period groups（P＜0.05）,and it also showed significantly seasonal difference（P＜0.05）, But there was no significantly difference in viability of sperms between two daylight period groups and seasons.
It was concluded that, the semen characteristics of dairy goat bucks in central Taiwan showed significantly seasonal variation, and the frozen semen quality was in accordance with the seasonal variation of fresh semen.
Keyword：Dairy goat bucks, semen characteristics, frozen semen, season.
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