Effect of different levels of Lysine and Threonine supplementation on performance, carcass traits and intestinal microflora of broiler chickens

Broiler chicks do not require to crude protein, but broilers require accurate and balanced amino acids. Researchers are trying to formulate diets based on digestible amino acids (Ciftci and ceylan, 2004) to meet the requirements of maintenance and production (Mack et al., 1999). Partial replacement for intact protein (e.g. soybean meal) with crystalline, amino acids brings the dietary protein closer to ideal protein and may allow for some decrease in dietary crude protein content (Bregendahl et al., 2002). A good number of studies showed that increasing dietary levels of lysine improved breast meat production (Mack et al., 1999). Lysine also impacts on the improvement of functional traits such as decreasing feed conversion and increasing body weight gain (Nasr and Kheiri, 2011). Threonine is particularly involved in maintenance processes, like the renewal of intestinal mucus and the synthesis of immune proteins. It has been estimated that more than half of the dietary threonine consumed by a piglet or a human is retained at the intestinal level to fulfill these gut-maintenance functions and is primarily used in the synthesis of mucins (Corzo et al., 2007). Mucin is a main factor in the protecting the mucosal layer of intestine, which acts as a layer protecting the intestinal underlying epithelium from infection and damage by infectious bacteria (Linden et al., 2008). This study was designed to determine the effect of added lysine and threonine on growth performance, carcass characteristics, and intestinal facultative anaerobic microflora of male broiler chicks from hatch to 21 and 42 days post-hatch.
Material and A total of 960 Ross 308 one-day-old female broiler chickens were selected and randomly distributed in a factorial design with 12 treatments, four replicates and 20 chicks in each replicate. The experimental diets include 4 levels of lysine (100, 110, 120 and 130% recommendation by NRC, 1994) and 3 levels of threonine (100, 110 and 120% recommendation by NRC, 1994). The diets were fed in two phases, starter from hatch to 21 days and grower from 22 to 42 days post-hatch. Birds and feed were weighed at the start and feed changes during the experiment and feed intake and BW gain was calculated and used to calculate FCR. On days 21 and 42, two birds from each pen with a BW close to the pen average were selected and euthanized by cutting the jugular vein after 3 hours of fasting. On day 21 and 42, a sample (two birds were sampled each pan the same one used for carcass) of the ileum contents was removed and to determine the total count of intestinal facultative anaerobic microflora, the sample was transferred to the microbiology laboratory. The obtained data were analyzed as a 3×4 factorial experiment in a completely randomized design with four replications using General Linear Models (GLM) procedure of SAS (SAS Inst. Inc., Cary, NC).
Results showed that different levels of lysine and threonine do not show significant effect on feed intake. Lysine levels, unlike threonine levels, influenced body weight gain significantly (P The best levels of lysine and threonine to achieve the most favorable values of carcass traits of broiler chicks are the level of 20% above from NRC recommendations. Regarding to the result of this study it was observed improving carcass traits, growth performance and reduction of intestinal facultative anaerobic microflora due to use 120% lysine and threonine. There was probably a relation between reduction of intestinal microflora and improving carcass traits and growth performance.