Growth, Nutrient Uptake and Immune Response of Broilers fed Dietary Tannins.

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Salim Gibril, Ahmed
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A series of experiments were carried out to investigate the effects of sorghum tannins on growth, nutrient uptake, gut wall histology, hematology and immune responses of broiler chickens. The study commenced with a survey (experiment 1) to determine the tannins contents of 7 sorghum cultivars grown in central Sudan. Sorghum cultivar cross (35x18) locally named Wad Ahmed showed the highest tannin contents (l6gCE/kg sample) followed by Gadam Hammam sorghum cultivar (7.5gCE/kg sample). Results indicated no relationship between seed coat colour and tannins content of the examined sorghum cultivars except that, Wad Ahmed and Gadam Hammam had red spots around their testae. Wad Ahmed was then selected to serve as the tannin source in the subsequent experiments throughout the course of this investigation. Tannin-containing diets based on this sorghum cultivar with groundnut meal, sesame meal and superconcentrate as protein sources were mixed to formulate the experimental diets. Diets were fed to commercial broiler chicks (Lohmann) in an open-sided deep litter poultry house. In experiment two of this study, three feeding trials were conducted to assess the effects of sorghum tannins on broiler chicks performance, nutrient uptake, gut histology and humoral immune response. Diets containing sorghum tannins at levels of 0 and 12gCE/kg diet were fed at 190 or 150 g protein /kg diet for three different durations. These were from day 4 to 5 weeks of age (Feeding trial1), from day 4 to 10 weeks of age (Feeding trial 2) and from 5 weeks to 10 weeks of age (Feeding trial 3), Results revealed that sorghum tannins fed at low protein level adversely affected (P<0.05) broiler performance, nutrient retention in all feeding trials and produced similar adverse effects on immune response in feeding trials 2 and 3. On the other hand results suggested that sorghum tannins had no effects on gut wall histology in all feeding trials and had no effect on immune response in feeding trial (1). Moreover, results indicated that sorghum tannins at high protein level produced no effect on bird performance and humoral immune response in feeding trial (2). Overall results revealed an adaptive response to dietary tannin at high protein level with time and that dietary tannins had no effect on gut wall histology. It can also be inferred that, sorghum tannins are immunosuppressant to broilers when fed at old age and at low protein level. The state of immunosuppression underlines sorghum use in human food. Experiment three utilized the same diets described in experiment two for the same durations to examine their effects on broiler hematological characters. In all experiments, Erythrocyte count, hemoglobin, packed cell volume, mean cell volume, mean cell hemoglobin and mean cell hemoglobin concentration showed no difference (P >0.05) between treatments. Hematological indices measured did not reflect anemia condition. Conclusion drawn from this study is that, time at which was introduced and the duration of its feeding at the two protein levels had no effect on blood physical characters and is not associated with anemia up to the level of tannins tested in this study. Experiment 4 tested the effects of feeding graded levels of sorghum tannins on broiler chick's performance, nutrient and mineral bioavailability, lymphatic organs weight and humoral immune responses. Tannins containing diets with graded levels (0, 4, 8 and 12gCE) were fed at 120 g protein/kg of diet for 7 weeks. Increasing tannin content of the diet resulted in a significant ((P<0.0l) negative linear decrease in performance and mineral bioavailability and a significant ((P<0.05) negative linear decrease in protein and ash intakes. Humoral immune response was reduced in a dose related fashion when tannins were incorporated into the diets at levels as low as 4gCE/kg of the diet. The relative sizes of the bursa of fabricus, thymus and spleen were insignificantly reduced upon tannins increment in the diet. Results suggested that sorghum tannins decreased humoral immune response and produced no effect on cellular response as measured by lymphatic organs weight. Experiment 5 of this study was a pair feeding trial designed to investigate the presence of other deleterious effects caused by sorghum tannins on broiler growth in addition to its depressive effect on feed intake. Diets with 12gCE/kg of sorghum tannins and without (0.0g CE/kg) were fed on a restricted basis to 24 individually caged broiler chicks (12/diet) for 4 weeks. Results indicated that, body weight gain of broilers fed tannins were significiantly (P<0.05) lower than birds which consumed tannin free diets. It can be concluded from this experiment that, feed intake depression associated with sorghum tannins is not the only cause that depresses growth rate in broiler chicks; other factors may be considered. The effects of tannins from sorghum grains and Acacia nilotica fruits on broiler performance and cellular immune response were compared in experiment six. Tannins from each source were fed at graded levels(0, 6 and 12gCE of tannins/kg diet) for 7 weeks. Results showed a significant (P<0.05) depressing effect on performance as the level of tannins from the two sources increased in broiler diets. Birds fed sorghum tannins produced lower performance as compared to those fed Acacia nilotica fruits, but the two tannin sources produced similar cellular immune responses. In addition stimulation indices of lymphocytes from birds fed Acacia fruits showed an immunopotentiating property. It can be inferred from these results that, different sources of tannins may have different effects on broiler performance and that some dietary tannins may have beneficial effects at certain levels.
Growth, Nutrient Uptake, Immune Response,Broilers fed ,Dietary Tannins.