Worapol Aengwanich, Pornchai Sridama, Yupin Phasuk, Thevin Vongpralab, Parwadee Pakdee, Suporn Katawatin, and Suchint Simaraks

pp. 297 - 305

Abstract

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 ^oC 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 cell and HI titer for Newcastle disease were determined. On day 21, histopathology of lung, liver, kidney,
heart and bursa of fabricius of randomly selected broilers (n=36; 3 birds per experimental unit) were studied.
Total white blood cells (TWBC) of the birds were significantly increased on day 3 (P<0.05) and were highest
on days 7 and 14 then significantly decreased on days 21 (P<0.05). Monocytes were significantly increased
on day 3 (P<0.05). Lymphocytes were significantly increased on day 7, and were highest on day 14 (P<0.05).
On day 21, the value of lymphocyte was significantly lower than on days 7 and 14 (P<0.05), respectively.
Lympholytic cells were significantly increased on day 3 and 7 (P<0.05), respectively, but on day 21, lympholytic
cells were significantly decreased to lower value than on day 7 (P<0.05). Heterophils were significantly
increased on day 3 and 7 and then decreased on day 14 (P<0.05). Tissue injury and hemorrhage in broilers
under chronic heat stress caused leukocytosis, heterophilia, lympholysis and monocytosis. The size of lobules
within the bursa of fabricius in broilers receiving ascorbic acid at 800 mg/kg in the diet were larger than in
birds that received added ascorbic acid at 400, 200 and 0 mg/kg in their diets, respectively. Lymphocytes
and lympholytic cells were not significantly different among the ascorbic acid treatment groups. Besides, HI
titers of Newcastle disease at 800 mg/kg in the diet were significantly higher than the others (P<0.05). Apparently, adding ascorbic acid at 800 mg/kg in the diet could improve humoral immunity in broilers under
heat stress.