• Eimeria maxima (E. maxima) is the most frequent cause of intestinal damage resulting in Necrotic Enteritis in poultry.
  • In this trial, Orego-Stim had a significant benefit in supporting body weight gain and feed conversion ratio (FCR) in broilers challenged with E. maxima during the peak period of coccidia cycling.
  • Orego-Stim did not prevent coccidia cycling, however results indicate that supplementation prevented the later cycling of coccidia seen in the challenged control group. It is often this late cycling that has the most negative impact on broiler performance.
  • Overall results suggest Orego-Stim at 600 – 800 g/tonne is effective in supporting bird performance during challenge with E. maxima and is a natural solution ideal for use within existing rotation, or bioshuttle coccidiosis control programmes, as well as any programme where late breaking coccidiosis is suspected.


  • E. maxima is one of three primary coccidia affecting broilers and is the most frequent cause of intestinal epithelium damage that initiates conditions favourable for Clostridium perfringens to proliferate and produce toxins resulting in Necrotic Enteritis.
  • Natural oregano essential oil (OEO) has many properties, including antimicrobial, antioxidant and immunomodulatory functions. It has also been shown to have a direct impact on oocyst shedding (Southern Poultry Research Inc., 2018) and on increasing gut cell turnover (Tzora et al., 2016) to support healing and repair of the gut lining.
  • Orego-Stim Powder is a high quality eubiotic composed of 100% natural OEO. It has been extensively researched and trialled in controlled challenge models and has been shown to successfully support coccidiosis management programmes.



A trial was conducted with the Southern Poultry Research Group, Inc., in 2021 to determine the effectiveness of variable does of Orego-Stim Powder (OS) in reducing the negative effects of the coccidia E. maxima. 450 day-old male Ross chicks were assigned to five groups, with nine cages per group and ten birds per cage using a randomised complete block (Table 1). Birds were raised in Petersime style battery cages (stocking density 0.63 sq. ft/bird) in a solid-sided barn maintained under ambient humidity. On day 8, all birds except the negative control, were individually challenged via oral gavage with E. maxima (Dr Fuller of The University of Georgia strain) (75,000 oocysts per bird at 1ml dose). Body weight gain, intestinal lesion scores (Johnson and Reid, 1970), oocyst count and mortality were recorded until 28 days of age.

Table 1. Experimental Design

Experiment Group E. maxima Challenge1 Starter Crumble (0-28 days)*
Negative Control No
Challenge Control Yes
OS600 Yes Orego-Stim Powder 600 g/t
OS800 Yes Orego-Stim Powder 800 g/t
OS1000 Yes Orego-Stim Powder 1000 g/t


1Day of challenge 14: Gavage 75,000 oocysts/bird E. maxima at 1ml dose/bird.

*All dietary supplementation was added via the mixer into the feed.


coccidia results

  • At day 14, the OS800 supplemented group had the lowest oocyst counts of all challenge groups, and by day 21, the cycling had begun in the OS600 supplemented group (Figure 1).
  • By days 25 and 28, all of the oocyst output was declining, however cycling within the challenge control group was not completed, which may have indicated late oocyst cycling (Figure 2).
  • No significant difference in E. maxima lesions and intestinal scraping were found between the challenge groups.



weight gain and FCR results

weight gain and FCR


  • During the major cycling of the coccidia to day 14, all Orego-Stim supplemented groups had significantly better body weight gain than the challenge control (Figure 3) and had a numerically improved FCR (Figure 4).
  • By day 21, all Orego-Stim supplemented groups continued to have a numerically better body weight gain (Figure 5) and FCR (Figure 6) than the challenge control.
  • By day 28, with the birds on wire floors, the challenge group had a compensatory weight gain. However, whilst there were no significant differences in body weight gain and FCR between the challenge groups at study termination (data not shown for brevity), all Orego-Stim supplemented groups had lower mortality than the challenge control group, with OS600 resulting in the same mortality as the negative control (Figure 7).



In the absence of anticoccidials, Orego-Stim Powder can help maintain bird performance during peak cycling of E. maxima, to help support in the development of natural immunity against coccidia. This is important within high stocking density and floor pen production systems where coccidiosis challenge is high and compensatory growth may not occur.