Effects of dietary surpluses of methionine and lysine on growth performance, blood serum parameters, immune responses, and carcass traits of broilers

ABSTRACT We evaluated the effects of dietary surpluses (100%, 110%, and 120% of Ross recommendations) of methionine (Met) and lysine (Lys) on growth performance, blood serum parameters, immune responses, and carcass traits of broilers using a completely randomized design with a 3？×？3 factorial arrangement. Broilers fed a diet containing Met and Lys according to Ross recommendations had maximal growth performance. During the starter period, higher Lys decreased intake of feed, energy, and protein (linear, P？<？0.01) and weight gain (linear, P？=？0.01). A diet with 110% Lys decreased feed efficiency (quadratic, P？=？0.03) during the grower period and decreased the pre-slaughtered body weight (tendency; quadratic, P？=？0.10), and increased serum uric acid (quadratic, P？=？0.03). Dietary Lys level had an inverse correlation with serum phosphorus (linear, P？=？0.02) and immune response against Newcastle disease virus after the first vaccination (linear, P？=？0.03). There were Met？×？Lys interaction effects on serum glucose (P？=？0.01), and relative weights of the rectum (P？=？0.02) and liver (P？=？0.02). Taken together, our results indicate that dietary surpluses of Met and Lys provided no additional benefits in broiler performance