ABSTRACT. This experiment aimed to evaluate the efficacy of sugar cane extract (SCE) on the modulation of porcine immunity against pseudorabies virus (PrV) infection. Twelve-week-old experimental pigs were fed with SCE (500 mg/kg of body weight per day) for 3 days and challenged with PrV (2 × 10 5 TCID 50 ) on the second day. Pigs that were only challenged with PrV and without SCE-treatment served as controls. The leukocyte functional assays were performed on the 7th and 14th day post-PrV challenge. Our results showed a significant enhancement (P<0.05) of natural killer cytotoxicity, lymphocyte proliferation, phagocytic function of monocytes, and interferon-gamma (IFN-γ) production of CD4 + and γδ T cells in the SCE-treated pigs compared with the controls. In addition, SCE administration reduced the severity of clinical signs and brain lesion in the course of disease in PrV-challenged pigs. SCE-treated pigs showed a 12% growth enhancement compared with untreated controls. SCE administration had an immunostimulating effect on porcine immunity that may subsequently enhance protective activities against PrV infection which may be extensively applied in field for the prevention of infections. KEY WORDS: immunomodulation, interferon-gamma, leukocyte function, pseudorabies, sugar cane extract.J. Vet. Med. Sci. 68(3): 219-225, 2006 In recent years, porcine respiratory disease complex (PRDC) has become the major problem in most intensive pig farms causing massive economic loss. The causes of PRDC involve a complicated synergistic interaction between host immunocompetence, pathogens, and various stressors arising from the environment and management [28]. Pseudorabies virus (PrV) has been recognized as one of the most important primary pathogens for PRDC in fattening pigs [5,13,28] and antibiotics are commonly used to prevent secondary bacterial infections. As the abuse of antibiotics in veterinary medicine has been of particular concern from the viewpoint of public health, besides vaccination, major strategies against PRDC are to improve the managerial systems and environmental conditions and to modulate host immunocompetence.Sugar cane extract (SCE) is a natural product, which has displayed a wide range of biological effects including immunostimulation [11], anti-inflammatory activity [19], activity as a vaccine adjuvant [10], and anti-stress effects [4]. Studies on chickens indicate that SCE acts as an adjuvant and has a protective effect against Eimeria tenella infection [9]. Other effects of SCE including antibacterial activities [1,25], resistance to cold stress, and superoxide anion scavenging activity [26] have been reported. These results suggest that SCE can activate and enhance host natural immunity against infections. Our recent report also indicates that SCE can up-modulate porcine immunity, particularly in the enhancement of natural killer cytotoxicity which plays an important role in early viral infections [21]. Therefore, we are interested in elucidating the immunomodulatory function of SCE against vira...