Effect of distillers dried grains with solubles‐incorporated diets on growth, immune function and disease resistance in Nile tilapia (Oreochromis niloticus L.)

Feed is the primary expense for intensive tilapia production and protein is the most expensive component; therefore, substitution of expensive protein ingredients with lower cost ingredients, such as distillers dried grains with solubles (DDGS), would decrease feed costs. The production of DDGS has increased from 2.7 to 9.0 million tonnes from 2000 to 2005 (Renewable Fuels Association 2006). The production of DDGS will no doubt continue to increase and remain important as a feed additive. A number of studies have shown that DDGS with supplemental lysine can be a protein source in ¢sh diets (Webster, Tidwell & Yancey 1991; Webster, Tidwell, Goodgame, Clark & Yancey1992;Wu, Rosati & Brown1996;Wu, Rosati, & Brown 1997; Lim, Garcia, Yildrim-Aksoy, Klesius, Shoemaker & Evans 2007; Belyea, Rausch & Tumbleson 2004).While these studies clearly indicate the utility of DDGS as a protein supplement, they do not address the possible bene¢t of enhanced immunity from the yeast component, which may be as much as half the protein in DDGS (Belyea et al. 2004).Yeast and yeast components have been demonstrated to stimulate the immune system whenadded to the diets of ¢sh (Couso, Castro, Magarinos, Obach & Lamas 2003; Lara-Flores, OlveraNovoa, Guzman-Mendez & Lopez-Madrid 2003; Bridle, Carter, Morrison N Kumari & Sahoo 2006). This experiment was conducted to determine whether growth performance was aiected by the inclusion of 30% or 60% DDGS, with or without lysine supplementation, as a substitute for soy and corn meals in Nile tilapia diets, and also to assess the eiects of DDGS on immune function and disease resistance to Streptococcus iniae challenge. Nile tilapia bred and grown at the USDA-ARS Aquatic Animal Health Research Unit, Auburn, Alabama, were acclimated to the control diet for a period of 2 weeks. Thirty ¢sh (mean weight 6.7^0.4 g) were stocked in quadruplicate aquaria (57 L) ¢lled with 52 L of water. Aquaria were provided with £owthrough heated dechlorinated municipal water. Water temperature and dissolved oxygen averaged 28^1 1C and 4.2^1.2mg L respectively. Distillers dried grains with solubles were from US Energy Partners L.L.C., Russell, KS, USA. On an airdried basis, this ingredient contained 32.5% protein and 5.7 g kg 1 of b-glucans as determined by the American Association of Cereal Chemists method BG5/03 AACC 32^33 (N.P. Analytical Laboratories, St Louis, MO, USA). Five diets were formulated to contain approximately 30% crude protein and 11092 kJ of digestible energy per kilogram (National Research Council 1993). The diets contained 0%, 30% or 60% DDGS as partial substitutes, on an equal protein basis, for a combination of soy and corn meals (Table1). In addition, Diets 3 and 5 were supplemented with lysine hydrochloride, at 0.5% and 0.9%, respectively, to equal the lysine level in the control diet (Diet 1). Corn starch and celu¢l were used to adjust the levels of nitrogen-free extract and crude ¢bre respectively. Aquaculture Research, 2008, 39, 1351^1353 doi:10.1111/j.1365-2109.2008.02000.x