ORIGINAL ARTICLE Effects of ascorbic acid on cell mediated, humoral immune response and pathophysiology of white blood cell in broilers under heat stress Worapol Aengwanich 1 , Pornchai Sridama 2 , Yupin Phasuk 3 , Thevin Vongpralab 4 , Parwadee Pakdee 5 , Suporn Katawatin 6 , and Suchint Simaraks 7 Abstract Aengwanich,W., Sridama, P., Phasuk, Y., Vongpralab, T., Pakdee, P., Katawatin, S. and Simaraks, S. Effects of ascorbic acid on cell mediated, humoral immune response and pathophysiology of white blood cell in broilers under heat stress Songklanakarin J. Sci. Technol., 2003, 25(3) : 297-305 The purpose of this study was to conduct an experiment related to the effects of chronic heat stress on total white blood cell changes, pathophysiology of leukocyte and effects of ascorbic acid on lymphocytes, lympholytic cells and humoral immunity of New-castle disease of broilers under chronic heat stress. Randomized complete block was the design. One hundred-forty-four chickens were maintained at 33 +1 o C environmental temperature and on four levels of added ascorbic acid i.e. 0 (control group), 200, 400 and 800 mg/kg in diets for 21 days. On days 1, 3, 7, 14 and 21 of the experimental period, total white blood cells count, lympholytic 1 Ph.D. Student in Animal Science, Department of Animal Science, Faculty of Agriculture, Khon Kaen Univer- sity, Khon Kaen 40002, 2 D.V.M. (Immunology), Veterinary Biologics Center, Department of Livestocks Developement, Pak- Chong, Nakhon Ratchasima 30130, 3 Ph.D. (Animal Science), 4 Ph.D. (Animal Reproduc- tion), Assoc. Prof., 5 Ph.D. (Animal Science), Asst. Prof., 6 Ph.D. (Animal Physiology), Asst. Prof., 7 D.V.M., Ph.D. (Physiology of Reproduction), Assoc. Prof., Department of Animal Science, Faculty of Agriculture, Khon Kaen University, Khon Kaen 40002, Thailand. Corresponding e-mail : worapol.a@msu.ac.th Received, 19 September 2002 Accepted, 12 Febuary 2003