Pakistan J. Zool., vol. 45(4), pp. 1015-1020, 2013 Formononetin Influences Growth and Immune Responses in Broilers Muhammad Farooq Iqbal, 1,* Raja Nauman Ahmad Khan, 1 Malik Muhammad Hashim, 2 Tanveer Ahmad, 1 Asghar Ali Mian, 1 Kashif Ishaq 1 and Abdul Rehman 3 1 Faculty of Veterinary and Animal Sciences, University of Arid Agriculture, Rawalpindi, 43600, Pakistan 2 Department of Food Science and Technology, Gomal University, Dera Ismail Khan, Pakistan 3 Poultry Research Institute, Murree Road, Shamsabad, Rawalpindi, Pakistan Abstract.- Many in vitro studies indicate that flavonoids could exhibit a variety of potential beneficial effects as non-antibiotic feed additives. However, there is a dire need to ensure the in vivo contribution of flavonoids in animals. Present study was aimed at determining the growth promoting and immune modulating effects of formononetin in broilers. A total of 135 one day old Hubbard broiler chicks, randomly divided into 3 treatment groups, received a common basal diet with formononetin inclusion at 0 (control), 10 and 20 mg/kg of diet. The results indicated that 10 mg formononetin/kg of feed resulted in better FCR (P<0.05) from 21-42 and 0-42 days and significant increase in weight gain from 0-42 days of age. The dressing percentage was higher (P<0.05) in birds fed the diet supplemented with either 10 or 20 mg/kg of formononetin as compared to control group at 42 days of age. The dose of 10 mg/kg significantly enhanced the meat quality. Analysis of immunity related indices showed significant difference in the blood levels of PGE 2 , IL-10, IFN-γ and LTB 4 between the birds supplemented with either 10 or 20 mg formononetin/kg feed and control group depending upon the age of the birds. Overall, the results suggested that formononetin could positively affect the immune response and improve growth in broiler depending on their age and its dose. Keywords: Broiler, formononetin, flavonoids, immune modulating effects, feed conversion rate. INTRODUCTION Antibiotics are added at low concentrations to chicken feeds as growth stimulants to modify bacterial, protozoal or fungal populations. There are many reports regarding the beneficial role of antibiotics which have proven to be effective in improving the performance of poultry especially broilers (Harms et al., 1986; Rosen, 1996; Taylor, 1997; Engberg et al., 2000). However, veterinary feed antibiotics have resulted in the appearance of resistant strains of bacteria. Resistant bacteria which are also human pathogens may cause diseases that are difficult to treat. Even if the resistant bacteria are not human pathogens, they may still be dangerous because they can transfer their antibiotic resistant genes to other pathogenic bacteria (Barton, 1998; Khachatourians, 1998). The quest for non-antibiotic feed additives has included the testing of a number of phytochemicals. Flavonoids, a group of polyphenolic compounds, found mainly in fruits and vegetables, have gained increased attention ______________________________ * Corresponding author: mfmalik@uaar.edu.pk 0030-9923/2013/0004-1015 $ 8.00/0 Copyright 2013 Zoological Society of Pakistan especially for use in poultry as can be derived from a significant increase in the number of scientific publications since 2000. This appears to be strongly driven by the ban on most of the antibiotic feed additives within the European Union in 1999, a complete ban enforced in 2006, and on-going discussions to restrict their use outside the European Union (Windisch et al., 2008). The results of several in vitro studies indicate that flavonoids could exhibit a variety of potential beneficial effects, including antioxidant, antiviral, anti-allergic and anti- inflammatory activities (Manthey et al., 2001; Nijveldt et al., 2001;, Khan et al., 2010). The in vivo evidence, however, is conflicting and the real contributions of such compounds to animal performance (including health challenges) are still unclear (Skibola et al., 2000; Ferreira et al., 2002; Halliwell, 2007). Present study was, therefore, conducted to evaluate the effects of formononetin, an isoflavonoid, as non-antibiotic feed additive in broiler diet. MATERIALS AND METHODS Animals and dietary treatments A total of 135 one day old Hubbard broiler