Supplementation of reduced protein diets with L-arginine and L-citrulline for broilers challenged with subclinical necrotic enteritis. I. Growth, carcass yield, and intestinal lesion scores

Context: Improving immune status through nutritional adjustments may be part of an effective strategy to reduce reliance on antibiotic growth promoters for controlling necrotic enteritis (NE) in broiler chickens. Aims: This study examined the effect of dietary protein level and the replacement of crystalline L-arginine (Arg) with L-citrulline (Cit) in the reduced-protein diet on the performance of broilers challenged with subclinical NE. Methods: Ross 308 cockerels (n = 720) were randomly allocated to six dietary treatments, with eight replicates of 15 birds per pen, during a 35-day feeding experiment. The treatments were as follows: standard protein without NE challenge (SP-); standard protein with NE challenge (SP+); reduced protein (two percentage points lower crude protein) without NE challenge (RP-); reduced protein with NE challenge (RP+); RP+ plus added Arg (103% of RP, RPA+) and RPC+ where supplemental Arg in RPA+ was replaced with Cit. The first four treatments were considered as a 2 x 2 factorial arrangement, with factors being NE (- or +) and protein level (SP or RP). Treatments SP+, RP+, RPA+, and RPC+ were analysed by one-way ANOVA. Key results: Subclinical NE challenge reduced feed intake (FI), reduced body weight gain (BWG) and increased feed to gain ratio (FCR) from Day 0 to Day 35, increased intestinal lesion scores on Day 16, and reduced relative breast yield on Day 35 (P < 0.05). Feeding RP diets increased FI (P < 0.001), increased BWG (P < 0.01) and reduced FCR (P < 0.01) during the grower phase compared with SP diets when birds were challenged with NE. Birds in the RPC+ treatment had a lower overall FCR than did those in the SP+ treatment (P < 0.001). Birds in the RPA+ treatment had similar FI, BWG and FCR to those in the RP+ treatment (P > 0.05). Conclusions: Collectively, the results showed protective effects of replacing the supplemental Arg with Cit against NE in RP diets, as indicated by higher performance during and after the challenge.