الفهرس 
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Abstract
The present study aimed to investigate the effect of ZnO and n-ZnO administration on a complex set of growth and reproductive performances in V-line male rabbits throughout growing and maturation periods.
A total of forty-five V-line breed clinically healthy male rabbits obtained from local supplier, were used in this study. Moreover, 2 female rabbits of the same breed were kept to be used as teaser for semen collection. Their age was 6 weeks old with an average body weight (1.5 -1.6 Kg B.W.). After the end of the 2nd month old, male rabbits were randomly divided into 3 equal groups (15 rabbits/ group) and received the following diets throughout the study that extended for 6th months; 1st group (control group) received basal diet, the two other groups (2nd and 3rd groups) were fed on basal diet supplemented with 60 mg ZnO / kg DM and 60 mg n-ZnO/ kg DM. Two experiments were performed; 1st (growth experiment) and 2nd (reproductive experiment).
In the 1st experiment, all animals were used for a period of 3 months. Growth performance trials were determined monthly (at the end of the 3rd, 4th and 5th month of age) including; B.W., B.W.G.., FC and FCR. Individual blood sample was collected monthly from each buck and sera were separated for biochemical analysis of Zinc, SOD, CAT, T3, T4 and testosterone. At the end of the growth experiment (5th month of age), five rabbits from each group were euthanized randomly following the last blood sample collection and testes were harvested for AR gene expression and histological structure of testicular tissue.
In the 2nd experiment the rest of rabbit bucks (10 rabbits/ each group) were kept to complete the reproductive experiment that was extended for 3 months. Throughout this experiment, growth performances; B.W., B.W.G., FC and FCR were measured monthly. Individual blood sample was collected monthly from each buck and sera were separated for biochemical analysis of Zinc, SOD, CAT, T3, T4 and testosterone. Semen samples were collected from each buck, by artificial vagina using the two female teaser rabbits, during 6th, 7th and 8th months old (4 semen specimens were obtained monthly/ buck). Semen samples were collected for semen analysis examinations including pH value, ejaculate volume, percentage of sperm motility, percentage of life spermatozoa, percentage of dead spermatozoa percentage of sperm abnormalities, sperm-cell concentration. The mean value for each parameter was then, calculated monthly for each group. Additionally, an individual seminal plasma sample from the last semen sample was separated monthly from each buck and kept at -20OC for biochemical analysis of Zinc, SOD, CAT. At the end of the 8th month, rabbit bucks were euthanized following the last blood sample collection and testes were harvested for histological examination and androgen receptor gene expression.
Results of the present work revealed that, dietary supplementation of ZnO, in comparison with control, throughout the growing as well as reproductive experiments, induced significant (P ≤ 0.05) improvement in all the growth performance trials as indicated by the increase in B.W., B.W.G. and decrease in the FCR. Meanwhile, the results of FC throughout the study were nearly similar. On the other hands, the effects of n-ZnO dietary supplementation were reported to be time-dependant. In this context, n-ZnO dietary supplemented group exhibited significant (P ≤ 0.05) improvement in all of the previously mentioned growth performance trials over that of ZnO group during growing period. Also, the n-ZnO dietary supplemented group exhibited significant (P ≤ 0.05) improvement in B.W. at the 6th and 7th months of age, in comparison with that of control, as well as on the 6thmonth only in comparison with ZnO group. Moreover, results of FC throughout the maturation period were nearly similar among different groups. However, prolonged n-ZnO dietary supplementation was recorded to induce significant (P ≤ 0.05) drastic effects. In this respect, significant (P ≤ 0.05) reductions in the B.W. at the 7th and 8th months of age were noted in n-ZnO dietary supplemented group in comparison with ZnO group. Beside, significant (P ≤ 0.05) drastic effect in B.W.G. and FCR in the n-ZnO dietary supplemented group throughout maturation period in comparison with ZnO group, as well as at the 7th and 8th months of age in comparison with that of control group.
Regarding serum biochemical changes, the current study showed that ZnO dietary supplementation induced significant (P ≤ 0.05) increase in serum levels of Zn, SOD and CAT as well as testosterone, in comparison with the control group, throughout the growing as well as reproductive periods. However, the changes in SOD and CAT as well as testosterone in serum of n-ZnO dietary supplemented group seemed to be time dependent, where these parameters increased significantly (P ≤ 0.05) in serum during growing as well as at 6th month of age only of the maturation period. It was also noted that, n-ZnO dietary supplemented group exhibited significant (P ≤ 0.05) increase in the serum levels of Zinc all over the growing and maturation periods. It was also clear that the positive effects of n-ZnO on the above mentioned parameters seemed to be higher than that of ZnO.On the contrary, significant (P ≤ 0.05) drastic effects were observed in serum levels of SOD and CAT as well as testosterone at 7th and 8th months of age in n-ZnO dietary supplemented group. Regarding the serum levels of thyroid hormones, it was found that ZnO didn’t induce any significant changes in the levels of T3 and T4 during the growing and reproductive periods as compared to control group. Similar finding were obtained in n-ZnO dietary supplemented group during growing period and up to the 6th month of age of the reproductive period. Meanwhile at 7th and 8th months of age, n-ZnO induced significant (P ≤ 0.05) drastic effect on levels of both hormones, as compared to both control as well as ZnO groups.
Aforementioned changes in the serum parameters including Zinc, SOD and CAT come in parallel with their changes in seminal plasma, the finding which indicates that seminal plasma considered as a mirror for serum components.
Results of AR gene in the testicular tissues revealed that ZnO dietary supplemented group showed significant (P ≤ 0.05) increase at 5th and 8th months of age, as compared to control group. Similar effects were also, obtained in the n-ZnO dietary supplemented group, at the 5th month of age only. However, on 8th month of age, n-ZnO dietary supplemented group displayed significant (P ≤ 0.05) reduction in the AR gene expression when compared to control as well as ZnO groups.
Regarding the influence of ZnO as well as n-ZnO dietary supplementation on semen characters during maturation stage of V-line male rabbits, the current work showed that, there was significant (P ≤ 0.05) improvement in semen characters in the ZnO dietary supplemented group as well as at the 6th month of age in n-ZnO dietary supplemented group, as compared to control group. Moreover, n-ZnO dietary supplemented group exhibited significant (P ≤ 0.05) improvement over that of ZnO dietary supplemented group in the displayed semen characters early in the maturation period; 6th month of age. Conversely, n-ZnO supplementation induced significant (P ≤ 0.05) drastic effects in the examined semen characters at the 7th and 8th months of age, as compared to both control as well as ZnO groups.
Microscopical picture of V-line rabbit testicular tissue at the end of the growing period; 5th month of age, revealed that ST belongs to ZnO group showed early maturation with a limited number of spermatozoa which are attached to Sertoli’s cells. While, ST of n-ZnO group showed spermatogenic activity with spermatid and spermatozoa in higher density than ZnO group. On the other hand at 8th month age, ST of ZnO group were highly packed with spermatozoa while, ST of n-ZnO group showed lower density of spermatid and spermatozoa with necrobiotic changes and increased number of multinucleated giant cells.
It could be concluded that dietary supplementation of either ZnO or n-ZnO at a concentration of 60mg/kg ration can be considered as an essential tool for improving growth and reproduction in V-line male rabbits. However, there were some differences between the effects of both supplements in regard to the potency of their effects as well as duration of application.