| Summary: | 博士 === 國立成功大學 === 生命科學系碩博士班 === 93 === Vitamin E was originally described as a dietary constituent required for normal reproduction in rats. Subsequently, it was recognized as an essential vitamin for maintaining the integrity of biological cell membranes. Vitamin E was also one of the nutrients that have been reported playing a role in immune function. Due to the rare data in its effects on chicken, effects of dietary vitamin E on 1) female reproduction, 2) male reproduction, 3) immune response and 4) antioxidant status were studied in Taiwan native breeder chickens.
Experiment I — female reproduction. This study was conducted to determine adding graded levels of vitamin E after the onset of laying on the reproductive outcome of breeder pullets.
Day-old female chicks were fed on corn-soybean growing diets without supplemental vitamin E from hatch to 17 weeks of age. After 17 weeks the pullets (n = 300) were randomly assigned to 5 dietary treatments and fed on corn-soybean laying diets supplemented with 0, 40, 80, 120 and 160 mg/kg of vitamin E (dl-α-tocopherol acetate), respectively, until 46 weeks of age. A flock of 15 cockerels were fed with practical diets throughout the experiment for semen collection and artificial insemination (AI).
The results for female reproduction indicated that addition of 120 mg/kg of vitamin E lowered the first egg weight (P < 0.05); however, there was no significant difference in the age or body weight of pullets at first egg or mortality rate to 46 weeks of age among the treatments. Supplemental vitamin E improved body weigh gain of laying hens during peak-laying period. Feed efficiency and egg mass were improved (P < 0.05) in pullets fed 80 mg/kg of supplemental vitamin E. A significant increase in egg production was observed after peak egg production in pullets given 80 mg/kg of supplemental vitamin E. However, this favorable effect decreased as supplemental vitamin E exceeded 80 mg/kg. Egg quality decreased with age. There was no correlation between age and fertility or hatchability during the experimental period, suggesting that egg quality is more age-sensitive than reproductive performance for breeder pullets. Compared with the control, fertility and hatchability of all eggs set for the treatment with 80 mg/kg supplemental vitamin E increased by 7.7 and 13.4%, respectively. There was no difference in the hatchability of fertile eggs. These results suggest that using supplemental vitamin E during the laying period can improve the reproductive performance of breeder pullets. The addition of 80 mg/kg of vitamin E obtained the best performance in egg production, egg mass, feed efficiency, hatchability and fertility.
Experiment II —male reproduction. This study was conducted to investigate effects of supplemental vitamin E on reproduction of cockerels.
Day-old male chicks were fed with corn-soybean rearing diets without supplemental vitamin E for 23 weeks. The cockerels (n = 90) were then randomly assigned to five groups and fed with the corn-soybean basal diets supplemented with either 0, 20, 40, 80 or 160 mg/kg of vitamin E (dl-a-tocopherol acetate) for 29 weeks. A flock of 225 pullets were fed with practical diets throughout the experiment. They were artificially inseminated with one dose of intact and five-fold diluted pooled semen (0.04 mL/bird) at 31 to 43 weeks and at 49 weeks of age, respectively.
The results for male reproduction indicated that supplemental vitamin E did not affect cockerels’ effective duration of fertility and percentage of fertility throughout the experiment. However, supplementing 160 mg/kg vitamin E significantly increased the maximum duration of fertility at 49 weeks of age, when pullets were inseminated with diluted semen. Cockerels fed diets supplemented with 40 to 160 mg/kg vitamin E had significantly higher sperm viability and motility after 39 weeks of age and those fed 80 mg/kg vitamin E had significantly higher sperm concentration at 39 weeks of age. Cockerels fed on diets supplemented with more than 40 mg/kg vitamin E had higher body weight gain in the experimental period. This results suggest that long-term (52 weeks) without supplemental vitamin E was associated with lower semen quality in the cockerels. Although it did not cause vitamin E deficiency syndrome. We could not demonstrate that lack of supplemental vitamin E caused impairment of male fertility, in terms of the proportion of fertile eggs laid by inseminated hens, since the insemination dose may have compensated for low sperm quality. We did find that the maximim duration of fertility might be improved by supplementing 160 mg/kg vitamin E at 49 weeks of age.
Experiment III — immune response. This study was conducted to investigate effects of supplemental vitamin E on immune status of female and male birds.
Supplemental vitamin E did not affect immune response of laying hens. For cockerels, dietary addition of 20 and 40 mg/kg vitamin E had a positive effect on immune response to sheep red blood cell (SRBC) and supplementation of 20 mg/kg vitamin E had the highest antibody titer to infectious bursal disease virus (IBDV). However, supplementation of 80 to 160 mg/kg vitamin E had lower immune response to SRBC and IBDV. These results suggest that moderate supplementation of vitamin E had shown to enhance immune responses to SRBC, whereas for selective antigens such as IBDV depression may occur when supplementation level is over 80 mg/kg. We suggest that supplementation of 20 mg/kg vitamin E to corn-soybean diet was optimal for enhancing immune response of cockerels.
Experiment IV — antioxidant status. This study was conducted to investigate effects of supplemental vitamin E on antioxidant status of female birds and hatching chicks. Hatching chicks form each treatment were sacrificed for evaluating effects of maternal vitamin E supplementation on antioxidant status of chicks.
Plasma vitamin E concentration of pullets increased linearly (P < 0.001; r = 0.997) as the increase of supplemental vitamin E, but egg yolk concentration reached a plateau at 120 mg/kg supplemental vitamin E. The malondialdehyde (MDA) levels, an indicator of lipid peroxidation, of hen plasma and chick brain significantly decreased as the increase of supplemental vitamin E (P < 0.05). Same results were found in the reactive oxygen species (ROS) levels, an indicator of oxidative stress, of chick brain and liver. For antioxidant enzymes, pullets given 120 mg/kg and 160 mg/kg of supplemental vitamin E significantly increased (P < 0.05) activities of catalase (CAT) of chick liver and superoxide dismutase (SOD) of chick brain, respectively. These results indicated that supplemental vitamin E could easily transfer to plasma and egg yolk of pullets. In addition, maternal supplementation of high levels of vitamin E (120 to 160 mg/kg) has beneficial effects on enhancing antioxidant capability and depressing oxidative stress of hatching chicks.
In conclusion, these data suggest that supplemental vitamin E improve reproductive performance of female chickens better than male chickens. Supplemental vitamin E exhibit beneficial effects on enhancing antioxidant capability and depressing oxidative stress of hatching chicks. Moderate supplementation of vitamin E may enhance immune responses to SRBC, whereas for selective antigens, such as IBDV, depression may occur by high supplemental vitamin E.
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