EFFECTS OF RESTRAINT FEEDING AND HIGH DOSES OF ZINC ON OVARIAN STRUCTURE, HORMONAL PROFILE, INDUCTION OF MOLTING AND ZINC ACCUMULATION IN ORGAN TISSUES OF WHITE LEGHORN LAYER BIRDS

Abstract

The present study was conducted to evaluate the effect of zinc oxides on reproductive structure and function in young laying birds (23 weeks of age) and old laying birds (65 weeks of age). Zinc is an important micronutrient in animal metabolism and in poultry. It is used as a dietary supplement to manipulate the reproductive system of the bird. For this purpose two experiments were conducted, Experiment-I and Experiment-II. In Experiment-I, birds were divided in four groups. Treatment to these birds was given for 12 days. At 25 weeks of age five birds from each group were slaughtered. In the remaining five birds of each group treatment was withdrawn and they were kept on normal feed for a period of 15 days. The birds slaughtered after 12 days of treatment were designated as Batch-I and those slaughtered on 15 th day after the withdrawal of treatment were designated as Batch-II. In Batch-I before the start of treatment their initial body weight was recorded and after treatment body weight was recorded after every two days. Linear regression analysis of variance showed that zinc administration and off fed conditions caused significant decrease in body weight over the period of twelve days in all treatment groups. Mean comb length decreased significantly in Group-II (off fed), Group-III (25,000ppm Zn/Kg feed) and Group-IV (30,000ppm Zn/kg feed) compared to Group-I while comb width decreased only in Group-III. In Group-II (off fed) wattle length and width significantly reduced compared to that of Group-I. Mean ovarian weight and length reduced significantly in Group-II (off fed), Group-III (25,000ppm Zn/kg feed) and Group-IV (30,000ppm Zn/kg feed) compared to Group-I. Reduction in ovarian weight in Group-II was higher compared to zinc treated groups. Mean oviductal weight and length also decreased significantly in all treatment groups compared to Group-I. Oviductal length in Group-IV showed higher reduction compared to other two treatment groups (II & III). The liver weight of birds in Group-II (off fed) and Group-IV (30,000ppm Zn/kg feed) showed significant decrease, however, reduction in Group-II was greater compared to zinc treated groups. There was significantly higher zinc deposition in the ovary, liver and kidney of Group-III (25,000ppm zinc/Kg feed) and Group-IV (30,000ppm zinc/kg feed) but Group-II (off fed) showed no significant change compared to that of Group-I (control). The deposition of zinc in Group-IV was higher compared to Group-III. Significant reduction in mean plasma concentration of estradiol and progesterone in Group-II, Group-III and Group-IV was observed on 3 rd , 6 th , 9 th and 12 th day of experiment compared to the levels in Group-I (control). Linear regression analysis of variance showed highly significant decrease in plasma estradiol and progesterone concentration in Group-II (off fed), Zn treated Group-III (25,000ppm/Kg feed) and Group-IV (30,000ppm/Kg feed) over the period of 12 days. Mean plasma level of corticosterone started increasing significantly in Group-II, Group-III and Group-IV from 3 rd day of treatment and remained elevated on 6 th , 9 th and 12 th day of experiment compared to the level in Group-I (control). Linear regression analysis of variance showed highly significant increase in plasma corticosterone concentration in all treatment groups with the advance in the days of treatment. In Batch-I mean number and diameter of yolky follicles reduced highly significantly in Group-II (off fed), Group-III (25,000ppm zinc/kg feed) and Group-IV (30,000ppm Effects of restraint feeding and high doses of zinc on ovarian structure, hormonal profile, induction of molting and zinc accumulation in organ tissues of White Leghorn layer BirdsAbstract zinc/kg feed) compared to the control. Due to the effect of these treatments large yolky follicles did not develop in treatment groups. Histomorphological measurements of ovarian follicular diameter showed highly significant reduction in all treatment groups, it was off fed group and high zinc treatment which had severe effect on reduction of follicular diameter in all categories above ≤200μm. Similarly, mean ovarian oocyte diameter significantly reduced due to feed withdrawal and two dosages of zinc. Compared to zinc treatments, feed withdrawal had more severe effect in reducing the ovarian oocyte diameter. Mean follicular wall thickness had also reduced significantly in all treatment groups but the effect was more severe in off fed and high zinc dosage group. Food withdrawal and high zinc dosage (30,000ppm zinc/kg feed) had highly significantly reduced the mean ovarian follicle number per section compared to Group-II (25,000ppm zinc/kg feed) in category ≤200μm. Group- II also showed significant decrease in mean ovarian follicle number in category 201- 400μm compared to control group. Histological study showed less number of follicles which possessed unclear and shrunken nuclei, abnormal oocytes with disrupted ooplasm, disrupted zona pellucida layer, absence of demarcation between granulosa and basal lamina, reduction in thickness of follicular epithelium, loose thecal layer with less number of thecal gland and increased number of atretic follicles and stromal tissue arrangement with more interstitial spaces in all treatment groups compared to control group. In Batch-II (Experiment-I) where birds were of 25 weeks of age and were slaughtered after 15 days of withdrawal of all treatments. Due to withdrawal of treatments, regression analysis of variance showed that mean body weight increased significantly in all the previously treated groups. In the case of secondary sexual characteristics comb and wattle length and width were comparable to the control, but in the low zinc treatments comb and wattle length and width increased significantly compared to control. Both in Batch-I and Batch-II zinc deposition in ovary was highly significant compared to the control. In contrast to Batch-I, in Batch-II there was no significant difference in zinc deposition in kidneys in treatment groups compared to the control. However, as with Batch-I, in Batch-II there was significant deposition of zinc in liver of treated groups compared to the control. Ovarian weight, length and width; oviduct weight and width and weight of liver responded differently after withdrawal of treatments. There was no statistical difference in ovarian weight in treatment groups compared to the controls. However, ovarian length in Group-II and Group-IV was significantly low compared to the control. Similarly, oviduct weight was significantly lower in Group-II and oviduct length was significantly low in Group-II and Group-IV compared to the control. Mean liver weight decreased significantly in Group-II and Group-IV. In Batch-II (Experiment-I) withdrawal of treatments resulted in the increase of plasma estradiol and progesterone in all the treated groups, however, plasma progesterone levels increased to the level of control group. Linear regression analysis of variance showed significant increase in plasma progesterone and estradiol levels with the passage of time. In the case of corticosterone with advancing days of withdrawal of treatments linear regression analysis of variance showed highly significant decrease in concentration in all the three treatment groups. Mean ovarian yolky follicles number and size increased significantly in all the treated groups particularly small sized Effects of restraint feeding and high doses of zinc on ovarian structure, hormonal profile, induction of molting and zinc accumulation in organ tissues of White Leghorn layer BirdsAbstract ovarian yolky follicles and large sized yolky follicles also appeared, which were not present during treatment period. In the case of ovarian follicular diameter there was no significant difference in the treated groups and control birds. However, there was significant reduction in ovarian oocyte diameter category up to 801-1000μm and follicular wall thickness compared to the control. Perhaps, influence of the treatments persisted after withdrawal of the treatments. Re-feeding resulted in the increase in the mean number of ovarian follicles in all the treatment groups. Results of Batch-II showed that the stress of the treatments vanished due to withdrawal of the three treatments. Histological study of Batch-II showed increased number of follicles possessing very clear and spherical nuclei, normal oocytes with ooplasm, zona pellucida layer, very clear demarcation between granulosa and basal lamina, thickness of follicular epithelium improved, compact thecal layer with number of thecal gland and no atretic follicles. The stromal tissue arrangement also improved. Experiment-II was started on the same pattern as that of Experiment-I with the difference that older birds of the age of 67 weeks were used. This experiment was also divided into Batch-I (in which 5 birds were slaughtered after 12 th day of molting) and Batch-II (in which remaining 5 birds were slaughtered after 15 days of withdrawal of all the treatments). In Batch-I (Experiment-II) there were four groups i.e. Control Group; Feed Withdrawal Group; Low zinc dosage (25,000ppmzinc/kg feed; High zinc dosage (30,000zinc/kg feed. During treatment period the same features, as with Experiment-I, were studied. Compared to the control, body weight was lost highly significantly in feed withdrawal group and both the groups treated with low and high zinc dosage. Mean ovarian weight, length and width, oviduct weight and width as well as liver weight significantly reduced due to these treatments, significant deposition of zinc in ovary, liver and kidney was observed in zinc treatment groups. As in Experiment-I, plasma estradiol and progesterone levels highly significantly decreased. Linear regression analysis of variance showed highly significant decrease in plasma estradiol and progesterone concentration in all treatment groups over the period of 12 days. Corticosterone level increased significantly from 3 rd day of treatment and remained elevated on 6 th , 9 th and 12 th day of experiment compared to the level in Group-I (control). Linear regression analysis of variance showed highly significant increase in plasma corticosterone concentration in all treatment groups with the advance in the days of treatment. Mean ovarian yolky follicle number, ovarian yolky follicles diameter, ovarian follicular diameter, oocyte diameter and follicular wall thickness reduced significantly due to these three treatments. Histomorphological changes showed decrease in number of ovarian follicles, that were disintegrated and disrupted, loose thecal granulosa layer. Large number of atretic follicles, loose thecal layer, scanty thecal glands and disrupted tissue were observed. This was more pronounced in feed withdrawal group (off fed). Stromal tissue in treated groups was loosely arranged and lacunae were also observed. When all the treatments were withdrawn (off fed, low and high zinc dosage), there was significant increase in body weight in all treated groups. Mean comb and wattle length and width increased in all groups during this period, however, in Group-II (off fed) it was still significantly less compared to control group. Ovarian and oviductal weight and length improved significantly. Ovarian length and width was significantly Effects of restraint feeding and high doses of zinc on ovarian structure, hormonal profile, induction of molting and zinc accumulation in organ tissues of White Leghorn layer BirdsAbstract low in Group-II and Group-IV. Similarly, oviductal weight and length also decreased significantly compared to Group-I. Linear regression analysis showed significant increase in estradiol and progesterone levels. There was highly significant decrease in plasma corticosterone concentration in Group-II, Group-III and Group-IV with the advance in the days of withdrawal of treatment. Ovarian yolky follicles number and diameter increased in all treatment groups. Ovarian follicular diameter, number, oocyte diameter and follicular wall thickness also increased significantly. There was significant improvement in histological changes were noted. Restoration of normal follicles, normal nuclei, zona pellucida attached to granulosa layer, and clear granulosa layer with basal lamina and thecal layer, normal thecal gland appeared as was seen in the control, stromal tissue was compact and no lacunae were seen. These results indicate that the treatment stress did not last long. This was neutralized as the treatments were withdrawn and normal feeding was restored. Molting lasted for 12 days. Egg production did not start but post-molting egg production was slow in the three treatment groups compared to the control. The lowest egg production in post- ovulation was seen in off fed group.