| Summary: | 碩士 === 國立中興大學 === 畜產學系 === 87 === Since, the Silkies in the market in Taiwan have already crossbreed with commercial broiler in nowadays, they have large body size, fast growth rate and good feed conversation ratio. But the blackness of their skin color varies, which usually confuses consumers and becomes a big problem for marketing. Owing to this problem, we designed two experiments to explore the effects of genetic, nutrition and hormone on skin blackness of Silky. In experiment 1, we used thirty-one male and two hundred and two female Silkies from a Silky breeder at Chiai as the parent stock. Color meter was used to measure the outer skin blackness of Silkies. Then they reproduced offspring for the study of the genetic characters of Silky by positive assortative mating. Moreover, we added 0%, 1% and 10% sesame meal in diet from 10-week-old on, to explore the effect of sesame meal on the outer skin and blood blackness of Silky. In Experiment 2, one hundred female Silkies from a Silky breeder at Yunlin were used to analysis the a-Melanocyte Stimulating Hormone (a-MSH) concentration in plasma and to extract the melanin content in the skin. They were used as the indicator of the skin blackness of Silky.
The results of experiment 1 indicated that the heritability of Silky skin blackness was in medium to high level（0.27-0.53）, therefore we could efficiently increase the Silky's outer skin blackness by selection. Females skin blackness were significantly darker than males at any age studied (P<0.01). Along with the increase of age, the skin blackness was getting lighter. Starting from 10-week-old, 0%, 1% and 10% sesame meal were added to the chicken's diet, and the variation of skin blackness was determined at 14 weeks of age. Because of the sampling random error, at 10 week of age, the skin blackness of Silky males fed with added 10% sesame meal diet were significantly lighter than the control. But this significant difference disappeared at 14 weeks of age. Besides, the skin blackness of females in treatment groups fed with added sesame meal diet was significantly darker than the control. If the differences of the skin blackness between after treatment（14 weeks of age）and before treatment（10 weeks of age）represents the treatment effect, the result clearly indicated that the supplement of sesame meal could inhibit the whitening of skin. The degree of whitening of the outer skin blackness of Silky feeding with added 10% sesame meal were significantly lower than the control. In the aspect of female Silkies, the inhibition effect on the whitening of skin blackness was significantly better in the treatment with 10% sesame meal than the treatment with only 1% sesame meal.
For the blackness of blood, there were no significant differences among treatments before the start of treatment (10 weeks of age). Whether supplementing with sesame meal or not, the blood blackness of every treatment reduced. No matter males or females, the reduction of blood blackness was significantly more in the treatment with 10% sesame meal than the other two groups. Due to the poor palatability of diet, the feed intake of the treatment with 10% sesame meal was significantly lower than the other two treatments from 10 to 14 weeks of age, and so as their body weight and body weight gain. Because of those reasons, feed conversation ratio (Feed Intake / Body Weight Gain) of the treatment with 10% sesame meal was worse than the other two treatments.
In experiment 2, the analyzed result did not suggest any relation between plasma a-MSH concentration and skin blackness. The blackness of Silky skin was measured by a color meter. The melanin content in the skin was then extracted. The correlation between blackness and melanin content was high and positive（r = 0.87, P＜0.001）. Therefore, it was not appropriate to use plasma a-MSH concentration as an indicator of skin blackness. The blackness of the skin measured by color meter can represent the melanin content of the skin.
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