DOI: 10.2478/alife-2018-0023 155 EFFECT OF THE DIETARY WILLOW BARK EXTRACT (SALIX ALBA) ON THE CAECAL MICROBIAL POPULATION OF BROILERS (14-28 DAYS) REARED AT 32˚C Mihaela SARACILA 1 , Cristina TABUC 1 , Tatiana Dumitra PANAITE 1 , CameliaPuia PAPUC 2 , Margareta OLTEANU 1 , Rodica DianaCRISTE 1 1 National Research- Development Institute for Animal Biology and Nutrition (IBNA), 1, Calea Bucuresti, Balotesti, 077015, Ilfov, Romania 2 University of Agronomic Sciences and Veterinary Medicine, Faculty of Veterinary Medicine, 105 Splaiul Independentei, 050097, Bucharest, Romania Corresponding e- mail author: mihaela.saracila@yahoo.com; mihaela.saracila@ibna.ro Abstract A feeding trial was performed on 60, Cobb 500 broiler chicks (14-28 days) assigned to 2 groups (C, E) housed in an experimental hall with 32˚C air temperature, 36% humidity and 23 h light regimen. The conventional diet (C), with corn and soybean meal as basic ingredients, had 3082.48 kcal/kg metabolisable energy and 19.99% crude protein. Unlike the diet of C group, the diet of experimental group (E) had 1% willow bark extract (Salix alba). At the age of 28 days, 5 broilers/group were slaughtered and samples of caecal content were collected for bacteriological examination. Compared to group C, the pathogenic bacteria, Enterobacteriacee and Escherichia coli (colony forming units), were significantly (P≤0.05) lower in the caecum content, while the units of lactobacilli were significantly (P≤0.05) higher in group E. Throughout the experimental period, under heat stress, no mortalities were recorded.The inclusion of 1% willow bark extract in broiler diets (14-28 days) reared under heat stress reduced the proliferation of pathogenic bacteria and stimulated the growth of favourable bacteria such as lactobacilli in the gut. Keywords: broiler, caecal microflora, gut health, heat stress, willow bark extract. INTRODUCTION Heat stress is one of the most important stressors confronting the poultry industry (Lara and Rostagno, 2013). The adverse effects of the heat on the poultry include depressed growth performances, altered gut microbiota and impaired integrity of the intestinal epithelium (Collins and Surette, 2012; Dinan and Cryan, 2012). Many studies aimed to develop strategies to control the adverse effects of the heat stress (Criste et al., 2017), among which feeding dietary additives to poultry (antioxi- dants, vitamins, minerals, growth promotors, prebiotics, essential oils). The use of antibiotics in poultry feeding alleviated, for a long time, the adverse effects challenging poultry growth. However, the use of dietary antibiotics was thereafter considered to be a risk factor for human health, as it promotes the resistance of pathogen bacteria to antibiotics, while antibiotic residues have been detected in poultry tissues. This made the EU to ban, in 2006, the use of antibiotics as growth promoters in poultry feeding (EC Regulation No. 1831/20031) (Wray and Davies, 2000). Therefore, animal feeding is highly interested to find alternatives, natural ones preferably, to the antibiotics used in poultry feeding (Hertrampf, 2001; Humphrey et al., 2002). For many years, the plants and plant extracts have been used as pharmaceuticals, as natural cure (Yang et al., 2009). The phytoadditives were found to have antimicrobial, antifungal, antipa- rasitic, antiviral, antioxygenic and insecticide properties (Burt, 2004, Okitoi et al., 2007; Hashemipour et al., 2013; Marin et al., 2015; Widjastuti et al., 2018). Like the antibiotics, but in a different extent, the phytoadditives can be potential stabilizers of the gut microflora eubiosis (Windisch and Kroismayr, 2007; Criste et al., 2017; Vlaicu et al., 2017). The white willow (Salix alba) is a tree with a long history of traditional use. There are about 500 willow species, growing mainly in Europe and North America.