The dietary treatments supplemented with increasing levels of either l-Met or dl-Met brought the Met content to 70, 80, or 90% of the Met + Cys requirement (Aviagen, 2007). Supplemental l-Met was obtained from a commercial company (CJ CheilJedang Co., Seoul, Korea), whereas dl-Met was commercially available and purchased locally by North Carolina State University Feed Mill (Raleigh, NC). Analyses verified that l-Met and dl-Met used in this study contained 99.1 and 99.2% active substance, respectively.