Over the past few decades broiler industry has showed great improvements in growth, increased efficiency of nutrient utilization. But advances in immune system improvement lag behind significantly. Endocrine system is also a participant in modulating immune response. One of these endocrine systems through which immune system can be modulated is through hypothalamus-pituitary-thyroid axis. Thyroid hormones are known for their role in immune organs development such as thymus and bursa of Fabricius. So this trial was designed to evaluate cell mediated and humoral immune response of birds during hyperthyroidism.
In this trial, one hundred day old broiler chickens were procured and maintained for 14 days. Then birds were divided into three groups. Group 1 received basal diet and served as control. Group 2 and Group 3 served as treatment groups and received 5 μg/Kg and 10 μg/Kg of thyroxine in addition to basal diet for 14 days. After 7, 14 and 21 days of trial, birds were bled and sampling was done. The parameters selected to assess immune response included blood collection for H:L, serum collection, macrophage engulfment performance, NO production assay, delayed type hypersensitivity reaction against phytohemagglutinin, heterophil to lymphocyte ratio, antibody titers against SRBC and viral diseases including ND and IB. Glucose tolerance test was also performed after 7, 14 and 21 days of trial. All the results for the parameters mentioned were analysed statistically using one way ANOVA. Results at p <0.05 were considered significant.
Results revealed showed that hyperthyroidism negatively modulates the immune response of birds. Macrophage phagocytic performance significantly declined, heterophil to
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lymphocyte ratio showed significantly higher. Results for NO production showed increase in control group followed by 10 μg group. Skin response to phytohemagglutinin remained nonsignificant. Antibody titers against SRBC, ND and IBV significantly dropped in birds subjected to hyperthyroidism. Glucose tolerance test showed significantly lower blood glucose levels in treatment groups as compared to treatment groups.
All these results suggest that hyperthyroidism can lead to deficient immune response in challenged birds and that physiological levels of thyroxine are sufficient for maintaining immune system.