Plasma Thyroid Hormone Concentrations and pH Values of Some GI-Tract Segments of Broilers Fed on Different Dietary Citric Acid and Microbial Phytase Levels

Problem statement: An experiment was conducted to study the effect of microbial phytase supplementation and citric acid on thyroid activity, relative weight of lymphoid organs and pH values of some GI-tract segments in broiler chickens fed corn-soybean meal based diets. Approach: The data was analyzed using a Randomized Complete Block Design (RCBD) with factorial arrangement of 3×3, three levels of citric acids (0, 3 and 6%) and three levels of phytase (0, 500 and 1000 IU kg⁻¹). There were three replicates (with ten chicks in each replicate) for each treatment. A total of 270 Ross 308 broiler chicks were used. Results: Addition of citric acid to diets caused significant decrease in pH values of crop, gizzard, duodenum, jejunum and ileum (p<0.05) and caused significant increase (p<0.01) in plasma triiodothyronine (T₃) concentration, T₃:T₄ ratio and relative weight of bursa and thymus, but had no significant effect on thyroxin (T₄) concentrations. Microbial phytase significantly increased relative weight of thymus (p<0.01), but had no significant effects on thyroid gland activity, relative weight of bursa and values of pH in different parts of the GI-tract. Conclusion: Broiler chicks fed on acidifiers diets had better immune response resistance that lead to immunological advances. Also, decreasing pH in GI-tract by CA caused a beneficial effect in the inhibition of intestinal bacteria competition.