Supplementation of reduced protein diets with L-arginine and L-citrulline for broilers challenged with subclinical necrotic enteritis. 1. Growth, carcass yield, and intestinal lesion scores

<p><b>Context.</b> 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. <b>Aims.</b> 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. <b>Methods.</b> Ross 308 cockerels (<i>n</i>= 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 × 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. <b>Key results. </b> 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 (<i>P</i> < 0.05). Feeding RP diets increased FI (<i>P</i> < 0.001), increased BWG (<i>P</i> < 0.01) and reduced FCR (<i>P</i> < 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 (<i>P</i> < 0.001). Birds in the RPA+ treatment had similar FI, BWG and FCR to those in the RP+ treatment (<i>P</i> > 0.05). <b>Conclusions. </b> 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. <b>Implications. </b> Feeding the RP diets supplemented with Cit may be part of an effective strategy to reduce reliance on antibiotic growth promoters for controlling NE in broiler chickens.</p>