Background update:Mar 9, 2016

Pro- and antibiotics in synergy against necrotic enteritis

New US field studies show that, in broilers induced with necrotic enteritis (NE), combining probiotics and in-feed antibiotics leads to better production performance than treatment with 
antibiotics alone.

Two NE challenge studies conducted at Southern Poultry Research in Athens, Georgia were designed to closely reflect conditions in commercial US poultry complexes. The purpose of the studies was to evaluate the impact on broiler performance with the addition of a probiotic supplement containing Bacillus subtilis to feed containing either BMD (bacitracin methylene disalicylate) or virginiamycin, antibiotics that have FDA-approved claims for growth promotion and the prevention of NE. “Results show that the probiotic-antibiotic combination regimens were associated with better weight gain and feed efficiency than either antibiotic alone,” according to Anée Berg Kehlet, poultry scientific manager for Chr. Hansen. “This suggests a synergistic effect of combining probiotics and in-feed antibiotics in broilers at risk of developing NE.”

Study design

The studies were conducted in conventional US poultry houses with earthen floors, built-up litter and standard heating and ventilation systems. All birds had unlimited access to feed and water throughout the 42-day observation periods. In each study, 1,080 healthy, vaccinated, male chicks were randomised 45 at a time to one of three different feed regimens, which were replicated eight times each.

All feed regimens were corn-and-soy-based, with recommended nutrient levels and salinomycin as a coccidiostat. Both studies included two control groups: one received neither probio-tics nor antibiotics (Group 1); the other (Group 3) received only antibiotics (Table 1). Group 2 in each study consisted of either virginiamycin or BMD, plus standard concentrations of a probiotic supplement containing B. subtilis as in GalliPro.

On days 19, 20 and 21 of the studies, all birds were exposed through feed to a local isolate of Clostridium perfringens known to cause NE. On day 22, five birds from each pen were euthanised and examined for NE lesions. On days 21, 35 and 42, average weight gain (AWG) and feed conversion (FCR) were assessed for each pen. Starter feed was used until day 21 of the study, grower feed until day 35, and finisher feed until day 42.


NE lesion analysis on day 22 confirmed that the disease challenge was successful in both studies and typical of subclinical infections found in commercial poultry production. On day 21, numerically higher weight gains and lower feed conversion ratios in both studies suggested an early benefit of probiotic supplementation (Tables 2 and 3). Throughout the duration of both studies, the probiotic groups continued to demonstrate the lowest feed conversion ratios. In the BMD study, the pro-biotic groups had consistently higher weight gain than either control group.

Enhanced intestinal performance

According to Kehlet, the better performance of the probiotic groups may be due to enhanced intestinal integrity and function. In previous studies, she said, broilers supplemented with probiotics had 9% longer villi than birds treated with only antibiotics. (Figure 1). “The longer the villi, the more surface area there is to absorb nutrients,” she explained. “The result is better weight gain, better feed efficiency and better overall performance.”

Probiotic-antibiotic synergies

Also, Kehlet said, probiotics work synergistically with 
antibiotics by balancing the microflora in the gut. “Probiotics complement antibiotics by keeping disease-causing bacteria in check — the more ‘good’ bacteria there are, the harder it is for pathogens to obtain the nutrition they need to grow,” she explained. “As these studies indicate, combining probiotics and antibiotics during intestinal challenge allows producers to meaningfully improve production performance, with no diet changes necessary.”

Chr. Hansen

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