Eimeria tenella oocysts were collected from infected broiler chicken’s cecal contents from broiler farms in Roi Et province, Thailand, and maintained at the Faculty of Veterinary Sciences, Mahasarakham University, Thailand. The oocysts underwent sporulation process in 2.5% (w/v) potassium dichromate at 30ºC for 48 hours. The sporulated oocysts were propagated in chickens; five commercial broiler chickens at 21 days old were inoculated with 2x104 sporulated oocysts. Then the cecal contents were collected at 7 dpi.
Animals and experimental design
Fifty-six, one-day-old commercial broiler chickens (Cobb) were obtained from a commercial hatchery. The chickens were randomly divided into 2 groups of 28 chickens each. The chickens in group 1 were not inoculated and group 2 were inoculated with 2x104 sporulated oocysts at twenty-one-day-old. Blood samples were collected from four chickens of each group and birds were then euthanized by cervical dislocation at 1, 2, 3, 4, 5, 6 and 7 dpi. The cecal tissues were collected from euthanized chickens. The chickens were fed ad libitum before and during the experiment. The experiment was reviewed and approved by the institutional Animal Care and Use Committee, Mahasarakham University (approval number: 033/2019).
The lesion scores of Eimeria tenella were obtained by examining the intestinal lesions of euthanized chickens at 1, 2, 3, 4, 5, 6 and 7 dpi. Scoring of lesions was recorded as described previously of Johnson and Reid (Johnson and Reid 1970): 0 = no sign, 1 = mild lesions, 2 = Moderate lesions, 3 = severe lesions and 4 = extremely severe lesions or death.
Fecal samples of each group were collected at 1, 2, 3, 4, 5, 6 and 7 dpi. The oocysts were processed in saturated sodium chloride solution and counted (oocysts/gram of feces) by using McMaster chamber under a light microscope.
Blood samples were collected from wing vein of chickens and transferred immediately into a sterile tube containing the anticoagulant (EDTA). Packed cell volume (PCV) was measured by using microhematocrit tubes and a hematocrit centrifuge, Total white blood count (TWBC) were performed in a 1:20 dilution of blood in Natt and Herrick’s solution. Differential white blood cell counts were made by preparation of thin blood smears stained with Wright’s stain and identified as lymphocytes heterophils eosinophils monocytes and basophils (Samour 2006).
Cecal tissue samples of infected chickens were fixed in 10% formalin, then processed embedded in paraffin and trimmed to 3-5 μm using a microtome. Tissue sections were according to histological techniques, stained with hematoxylin and eosin (Awad et al. 2008) and examined under a light microscope.
The lesion scores, oocyst per gram of feces and hematological data were analyzed using Mann-Whitney U tests with SPSS for windows (SPSS Inc, Chicago). Statistical difference was considered significant at p < 0.05.