A New Low Mortality Necrotic Enteritis Challenge Model

Necrotic enteritis (NE) in broilers – caused by Clostridium perfringens – is largely controlled by in-feed antibiotics in Australia. Alternatives to antibiotics are being sought by industry and must be tested under simulated outbreak conditions. An existing NE challenge model employed at UNE has demonstrated differences between NE intestinal lesion score between unmedicated challenged and unchallenged controls. However, up to 20% NE-related mortality was routinely observed in challenged groups without an antibiotic (Zn bacitracin). A different model was required to minimise mortality and improve the relevance of the data to industry. In the current study, a new NE challenge model was developed by removing a protein-fortified pre-challenge diet and replacing it with standard wheat-based starter and grower diets, formulated to broiler breed standard specifications.

A 2 × 2 factorial (± C. perfringens challenge, ± Zn bacitracin) design experiment was conducted to test the new challenge model. All birds (672 Ross 308 males divided into six replicates of each treatment) were fed the same formulations of starter, grower and finisher diets at 0-10, 11-24, and 25-35 days of age, respectively, except for Zn bacitracin which was applied according to the experimental design. The NE challenge procedure followed Wu et al. (2012). Total mortality for the 35 d study was 2.9% across all treatments, with only 1 death attributed to NE. Intestinal mucosa NE lesion scores (where; 0 = healthy, and 4 = widespread necrotic lesions) were recorded one day post challenge (table 1). Bird performance in all treatments exceeded 2012 breed performance objectives.

Table 1 - Mean post-challenge intestinal mucosa lesion scores

Duodenum, jejunum and average intestinal NE lesion scores were higher (P < 0.001) in the challenged, unmedicated treatment than medicated or unchallenged treatments.

The new model reduced NE mortality whilst maintaining adequate lesion scores to sufficiently separate treatments (controls in challenge studies). The newly developed model will be employed in future studies to identify potential non-antibiotic candidates to control NE, improve bird welfare and increase the relevance of NE challenge study data to industry.