Effect of zinc and selenium supplementation in diets of heat stressed broiler chick on growth performance and immunocompetance

الملخص EN

Two hundred and fifty one day old Hubbard chicks were divided into 5 groups (50 chicks each).

The first group (the control) was fed the basal starter diet (23% CP, 3200 KCal ME / Kg) for 3 weeks of age then the finisher one (18% CP and 3200 KCal ME / Kg) till the end of the experiment at 6 weeks.

At the beginning of the 3rd week, the other groups were fed the normal control diets (starter and finisher) supplemented with 40 mg Zn/Kg from Zn methionine or Zn sulfate or 0.15 mg Se / Kg as selenium enriched yeast or sodium selenite above the recommended levels of these minerals.

The different levels and sources of the supplemental minerals were added to the normal control diets fed to the experimental groups throughout the period from 3-6 weeks age, where the ambient temperature in the broiler pens were above 30°C (35°C - 38°C).

Body weight of the chicks and consumed diets were weekly recorded where the weight gain and feed conversion ratio was calculated.

Blood sample were collected from the wing vein of the broilers at 20, 30 and 40 days of age and the sera were analyzed for glucose, triglyc-erides, cholesterol, total protein, albumin, globulin and haemagglutin-ation test (Haemagglutination Inhibition HI titers against NDV and total antibodies).

At the end of the experiment specimens from liver, kidneys, spleen, and intestine were examined for histopathological changes.

The results revealed that supplementing the diets with the minerals during the 3rd week of age did not improved the growth performance of the heat stressed broilers fed the diets supplemented with zinc methionine.

Supplementing the used diets with zinc methionine and selenium organic during the period of heat stress significantly (p < 0.05) improved the body weight, body weight gain and feed conversion ratios recorded at the 4th, 5th and 6th weeks of the experiment.

The blood glucose regulating effect was more clear in serum of the broilers supplemented with dietary Zn methionine or organic Se.

Supplementing the diets of the heat stressed broilers with zinc or selenium decreased the serum triglyceride and decreased the cholesterol specially by organic source supplementation.

The levels of serum total protein, albumin and globulin increased in the broilers fed the diets supplemented with zinc or selenium.

Supplementing Zn or Se to normal diets in stress conditions improve the immune response and decrease the severity of the pathological changes which may be occur due to exposure to severe heat stress.

Therefore, from the present results it could be concluded that Zn and Se to the broiler diets may improve the immunocompetance and resistance to Newcastle and Gumboro viruses and alleviate effect of heat stress which induced suppression of antibody responsiveness.