By Dr Alexandra Desbruslais, Anpario
An edited version of this article first appeared in the Poultry Business feed and nutrition supplement, published in April 2025
Coccidiosis remains a key challenge for the poultry industry, with some estimates suggesting it costs the global poultry industry more than £13 billion annually, or 16p per bird produced. Clinical symptoms range from depressed performance through to chronic mortality, depending on severity and strain of the parasite.
Producers have developed and utilised numerous mitigation strategies over the years with varying degrees of success and cost to the producer. Ionophores and chemical anticoccidial agents have been used extensively since the 1930s, however with growing concern surrounding drug residues in meat and the increasing resistance of the Eimeria parasite to these compounds alternative strategies are required.
Oregano essential oil (OEO) has been widely shown to have excellent anticoccidial properties, offering both direct and complimentary effects. OEO is comprised of over 100 different phenolic compounds including carvacrol and thymol. Pure OEO has been shown to inhibit Eimeria sporozoite invasion due to its hydrophobic properties and low molecular weight which facilitates cell membrane permeability. This causes an increase in cytoplasmic membrane permeability and leads to cell death caused by leakage of ions, energy loss and diffusion of cell contents. In addition, the high lipid solubility of OEO permits rapid diffusion through parasite and host cell membranes.
Alongside this direct effect on the parasite OEO has been shown to significantly increase enterocyte turnover, which in turn disrupts the lifecycle of the parasite as Eimeria sporozoites are shed before they can penetrate deeper into the intestinal wall or form new oocysts. By creating a hostile environment for the Eimeria, the risk of clinical coccidiosis is dramatically reduced.
Furthermore, OEO supports the bird exerting anti-inflammatory, antioxidant and antimicrobial effects. Interestingly, there is increasing evidence to suggest that essential oils are far less likely to lead to resistance issues. This is because essential oils contain numerous active components that each work in a specific way, making it very difficult for microbes to evolve to become resistant.
The use of Oregano essential oil
Orego-Stim is a natural OEO-based supplement from Anpario. It has been shown to consistently support the health and performance of livestock. To demonstrate the effect of Orego-Stim in coccidiosis management a trial was conducted at a research facility.
200-day-old Ross 308 broiler chicks were randomly assigned to 20 homogenous groups of floor pens. Pens were randomly assigned to one of four treatments, with five replicates of ten birds per treatment. On day 22, all challenge groups were orally gavaged with mixed Eimeria species. Coccidial lesion scoring was carried out at day 28. Performance parameters were calculated for the entire experimental period at the end of the experiment (day 42).
Table 1: Experimental Design
150-fold dose of Livacox T, trivalent live attenuated coccidiosis vaccine on day 22 (each dose contained 300-500 sporulated oocysts of each of Eimeria acervulina, E. maxima, E. tenella).
Results
Across the entire production cycle there was no significant difference in body weight gain between treatments, however within the three challenged groups the OS500 group performed best during all time points (Figure 1).
Figure 1: Bodyweight Gain
There was no significant difference in FCR between the OS500 and the negative control group during days 1-21. However, compared to the PC, FCR was improved by 4 points in the OS500 group (Figure 2). From days 22-42 the OSP500 group had a 6-point improvement in FCR compared to the PC.
There was no significant difference in FCR between the OSP500 group and the NC group at any stage of the production cycle, suggesting that the OS group was able to perform as well as the unchallenged group of birds.
Figure 2: Feed Conversion Ratio
There was a significant improvement in the European poultry efficiency factor for the OS500 group compared to the positive control, demonstrating that despite the coccidiosis challenge, the application of OS facilitated the birds to perform statistically similarly to the unchallenged birds (Figure 3). Furthermore, the OS500 group achieved a higher EPEF score than the chemical anticoccidial group.
Figure 3: European poultry efficiency factor scores
Eimeria acervulina, E. maxima and overall lesion scores were significantly improved in the OS500 group compared to the PC group (P<0.05), and there was no difference from the NC group (P>0.05)
Overall, lesion scores were lower in the OS500 group compared to the chemical anticoccidial group (Figure 4).
Figure 4: lesion scores
When we consider the economic impact of this trial, taking an average feed cost of £350/mt plus the market cost of both the chemical anticoccidial and the Orego-Stim® (Table 2), the results show that the OS500 treatment would result in an additional £56,500 per 1 million birds produced compared to the positive control treatment, or an additional £9,500 compared to the chemical anticoccidial product. This demonstrated that the use of oregano essential oil can offer an effective, economical option to traditional anticoccidials without the risk of resistance or chemical residues in the meat.
Table 2: Economic analysis
