New research into feed additives to control Necrotic Enteritis

Necrotic enteritis (NE) in broiler chickens is caused by Clostridium perfringens. This disease has a large negative impact on the health of broilers and therefore on the profitability of commercial broiler operations. After the ban on antimicrobial growth promoters (AGPs), it is expected that incidence of NE will increase.

Organic acids (OA) have been used for decades due to their preservative (flora modulating) effects in feed and subsequently in the first parts of the gastro-intestinal tract. Medium-chain fatty acids (MCFA) have recently caught scientific interest due to their antibacterial effects.

In this research a product combining organic acids (formic, acetic, propionic, and sorbic acid) and medium-chain fatty acids (caprylic, and capric acid) was tested. In vitro research had already indicated a strong anti-clostridium effect from this product. The next step was to test the effect of this product in vivo. The research team used an experimental model with a two-step infection, first with Eimeria challenge and then with Clostridium perfringens. The animal performance and intestinal NE lesion score were measured. The hypothesis was that the experimental product would improve these parameters compared to an infected control group without additives. A medicated group with 50 g/ton of growth promoter Bacitracin Methylene Disalicylate (BMD) was also tested.

Materials and Methods

Five experimental treatments were tested (Table 1).

A non-medicated corn/soy commercial-type chicken starter ration was formulated. This ration (in mash form) was fed ad libitum from the date of chick arrival until day 28 of the experiment. Experimental treatment feeds were prepared from this basal starter feed. Treatment feeds were mixed at SPR to assure a uniform distribution of the test article. The product was tested in two quantities: 2 and 5 kg/ton of feed.

Table 1 – Experimental treatments

One-day-old male Cobb X Cobb broiler chicks were used. At the hatchery, the birds were sexed and received routine vaccinations. Only healthy appearing chicks were used. Upon arrival, chicks were raised in Petersime battery cages. At placement the birds were fed the treatment feeds. Assignment of treatments to cages was performed by SPR. Cages were blocked by location in the battery with block size equal to treatments.

Three control groups were used: a non-infected non-medicated group; an infected non-medicated group; and an infected medicated group (50 g/ton BMD).The study began when the test birds were placed (‘day 0’) at which time they were allocated to the experimental cages. No birds were replaced during the course of the study.

Feed and water were available ad libitum throughout the trial. On day 14, all birds were orally inoculated with a mixed coccidial inoculum containing approximately 25,000 oocysts of E. acervulina per bird and 5,000 oocysts of E. maxima per bird. This was done to sensibilise the birds for the subsequent Clostridium perfringens inoculation, which started on day 19. They were administered a fresh broth culture (108 cfu/ml) once daily for 3 days (on days 19, 20, and 21).

All birds were weighed by cage on days 0, 14, and 28. Feed was weighed in on day 0 and remaining feed was weighed on days 14 and 28. The trial was terminated on day 28.

On day 22, five birds from each cage were selected, sacrificed, weighed, and examined for the degree of presence of Necrotic Enteritis lesions. The scoring was based on a 0 to 3 score, with 0 being normal and 3 being the most severe. Data were analysed by t-test (2 tails) analysis of pairwise comparison. Table 2 shows zootechnical performance, and Table 3 shows NE lesion score as well as the mortality caused by NE.

Table 2 – Zootechnical performance

Results and Discussion

Clostridium challenge induced a severe NE infection (compare T2 with T1), with strong deterioration of weight gain and feed conversion. The average NE lesion score was 1.6 and the mortality was high (17.5%). Adding 2 kg/ton of OA/MCFA product improved weight gain and feed conversion (0-28 days) by 29% and 8% respectively. NE lesion score (day 22) was decreased by 22% and mortality tended to be decreased by 45%. A dosage of 5 kg/ton of OA/MCFA product did not further improve NE status and bird performance. BMD at 50 g/ton as positive control group, showed the strongest improvement with all parameters tested.

The improvements, as induced by the OA/MCFA product, were roughly equal for weight gain, feed conversion and mortality, when expressed as percentage of the NE infection effect (= difference between non-infected and infected negative control). Adding 2 and 5 kg/ton of OA/MCFA product compensated for about 45% of the negative impact of NE infection, and BMD compensated for about 75%.

The results of the OA/MCFA product are in line with previous in vitro work. MCFA inhibit gram positive bacteria by the so-called uncoupler effect, in contrast to organic acids which have their biggest effect in gram-negative bacteria. Therefore, it is hypothesised that the MCFA fraction in the tested product is mainly responsible for the observed effects on gram-positive Clostridium perfringens. Previous trials have shown that neither OA nor MCFA have any inhibitory effect on Eimeria infection, which rules out the possibility of an indirect effect of the product via the reduction of Eimeria lesions.

It seems that the proven preservative effects of OA and MCFA can be carried over to the intestinal tract flora. This opens opportunities for control of Clostridium-related enteritis problems in the field, especially in the light of a ban on AMGP and prudent us of feed medication. Still, it is clear that the effect of antibiotics cannot be mimicked to the same extent by natural substances like OA and MCFA; it is not clear in either case by what mode of action the anti-clostridium effects were obtained. It is therefore recommended to base NE control on multi-hurdle techniques including strict hygiene, proper coccidiosis control and optimisation of feed formula, of which the tested OA/MCFA product can be a part.

The trial shows that the tested OA/MCFA product shows mild anti-clostridium effects in vivo and fits well in a total approach to control NE. The recommended dosage is 2 kg/ton, because a higher dosage of 5 kg/ton did not provide additional benefits in terms of lesion scores or broiler performance.