New article: Coccidiosis in chickens and the use of oregano oil

The article 'Coccidiosis in chickens and the use of oregano oil' has been recently published by Feed Navigator, and can be downloaded here, or alternatively, read in full below.



Coccidiosis is a global disease of poultry, affecting birds reared on the floor or in cages at different times of their life. It is estimated to cost $2.4 billion globally, each year.



Coccidiosis is caused by the intracellular protozoal parasite Eimeria, belonging to the genus Apicomplexa. In chickens, it is generally accepted that there are seven species of Eimeria, and each species is specific to a host species, i.e. Eimeria in chickens do not infect turkeys and vice versa. Each Eimeria species also has a preference for a specific area of the gut and produces different severity of disease. For example, Eimeria tenella infections can result in haemorrhage in the caeca and death, whilst E. mitis can infect birds with very mild symptoms and is seldom associated with mortality. A cycle of reinfection of the parasite establishes in the poultry shed. The active infection occurs in the bird, followed by the excretion of hardy oocysts (resistant to many physical and chemical attacks) onto the litter before again being ingested by the chicken. Eventually immunity to Eimeria develops, but not before the gut wall is damaged, potentially lowering the birds' ability to secrete enzymes and mucus and reduce uptake of nutrients. There is also a risk of secondary infections occurring, such as Clostridium perfringens leading to Necrotic Enteritis (NE); coccidiosis is often a predisposing factor for NE.


Coccidiosis control

In 1939, Levine showed that sulphanilamide could be used to control coccidiosis in chickens and since that time various drugs, either chemical or ionophore, have been developed against Eimeria. The advent of chemotherapy in the 1940's was instrumental in building a platform for intensive poultry production. Thus, without anticoccidial drugs, modern poultry production might look very different. However, drug resistance has been a cause of great challenge for the poultry industry, including coccidiosis control. This has led to the implementation of shuttle and rotation systems, effectively changing the drug, either within the production cycle or between production cycles. Even with these practices, drug resistance is still a problem.


Anticoccidial vaccines introduced another approach to help manage coccidiosis in poultry production, although their uptake in modern poultry production (other than breeders) has not been as widespread as chemotherapy for a variety of reasons. For example, anticoccidial drugs are typically low cost, easy to apply and effective. In the case of ionophores they also have antibacterial properties. Commercial anticoccidial vaccines mainly fall into two groups: 1) non-attenuated strains of Eimeria that are similar to typical field strains or 2) attenuated, or precocious Eimeria strains. A third vaccine type based on Eimeria proteins has achieved some commercial success in limited markets. The precocious strains have a shortened life cycle that reduces the severity of infection, whilst still stimulating immunity. However, attenuated or non-attenuated vaccines still cause intestinal damage and take a minimum of 2 weeks to stimulate the beginnings of a protective immune response.


With the withdrawal of some existing chemotherapeutic products, the absence of new chemicals coming to market and the development of anticoccidial drug resistance, the tools to help manage protozoal poultry infections are becoming limited. Feed additives, such as those based on organic acids or phytogenics, are increasingly used in poultry production as alternatives for antibiotics and to help manage gut microbiota. A search of the scientific literature produces in excess of 200 manuscripts investigating phytogenics for the management of intestinal protozoa in poultry, indicating that this is an active area of research and potential commercial application.



The term phytogenics (often named phytobiotics, essential oils (EO), botanicals) broadly encompasses most products derived from plant origin and comprises a wide variety of herbs and spices. They are volatile, aromatic mixtures, primarily comprising terpenes and phenlypropanoids and are present in many plant tissues, where their function is to defend the plant from parasites. The composition of the oil can vary greatly, even within the same species, due to influences of soil type, season or climate, for example. An analysis of Oreganum vulgare from different altitudes in the Himalayas, indicated large differences in two phenols, carvacrol and thymol, with the content ranging from approximately 0.1-81.0 and 0.4-85.8%, respectively. Consequently, whenever EO's are considered for use in livestock production, an understanding of the EO production process and the implementation of specifications for oil composition, is absolutely essential to ensure consistency of product use and performance.


EOs are a relatively new class of feed additives but have displayed both in vitro and in vivo efficacy. EOs have been used for centuries in alternative human medicine due to their high content of pharmacologically active compounds and, like organic acid feed additives, are classed with GRAS status in the USA. Furthermore, EO use is versatile as they can be used in water or added to the diet easily without residual effects.


Phytogenics and Eimeria

A recent study compared the anticoccidial effects of lasalocid, Artemisia annua (leaf powder) and a mixture of oils of A. annua and Foeniculum vulgare (Fennel) added to diets fed to chicks. Birds were later challenged with E. tenella in a floor-pen trial. The researchers found that birds treated with A. annua powdered leaves had comparable lesions scores to the lasalocid group and significantly lower lesion scores than birds in the positive control group, supporting the use of phytogenics for this application. Work with extracts from Plantago asiatica (a plant used in traditional herbal medicine) fed to birds challenged with E. tenella, demonstrated an average 67% reduction in oocyst shedding. A mixture of peppermint and eucalyptus oil has been shown to improve weight gain percentage by 36% in addition to improving FCR and reducing intestinal lesions and oocyst counts, following a mixed Eimeria challenge.


An interesting piece of work in 2010 evaluated the effects of phytogenics (carvacrol, cinnamaldehyde and capsicum oleoresin) on gene profiles and coccidiosis resistance in broilers. Day old broilers were orally challenged with E. acervulina one day following hatch. Results from this study suggested that birds supplemented with capsicum oleoresin had induced gene changes that were associated with immunity, suggesting that these plant compounds possess immune-enhancing properties. In short, resistance to coccidial infection was shown to be greater in those birds receiving plant extracts, as well as further performance benefits in terms of body weight gain observed.


The earlier examples give a brief demonstration of the breadth of choice of phytogenics and their presentation. One such phytogenic is oregano EO.



Oregano oil is obtained by steam distillation and contains many compounds, mainly monoterpene hydrocarbons and phenolic compounds. Its active ingredients for use in animals includes carvacrol, thymol, γ-terpinene and p-cymene. Research has shown that carvacrol has antioxidant properties as well as antimicrobial properties and a role in modulating gut microflora. Carvacrol appears to have a differential influence on Gram negative and Gram positive bacteria, demonstrating greater activity against the Gram negative bacteria. Various published papers have shown that oregano extract has an impact on digestion and performance in broilers, as well as some immunity and hind gut microflora benefits. A recent trial using various levels of oregano in broiler diets showed that 600 g/t feed, improved weight gain and FCR at 42 days of age. Populations of Gram negative E. coli were significantly reduced in birds fed 300 g/t or more oregano in the diet, and antioxidant serum markers were numerically increased. Oregano has been shown to lower the production of anti-inflammatory cytokines in human cell lines, as well as stimulate the activity of macrophages and positively influence gut morphology.


Oregano and Eimeria

The earlier mentioned properties of oregano are important when the essential oil is used to influence the effect of Eimeria in challenged birds. In birds challenged with Coccivac B-52, oregano was shown to lower the production of inflammatory cytokines. Indeed, in this particular study, the cytokine reduction was greater than other compounds such as purified and primary yeast cell wall extracts, Salinomycin and a probiotic. In a further challenge study using E. acervulina and E. maxima (at 14 days of age), broilers receiving diets supplemented with oregano (Orego-Stim) at 0.03 or 0.06% had similar performance to both the non-challenged control and a group receiving Salinomycin. The performance of all these groups was better than the challenged control. Similar effects have been seen in other studies.


In work published in 2013, the direct effect of carvacrol and thymol on Eimeria oocysts was clearly shown. Measuring a wavelength of light (273nm) specifically absorbed by the contents of oocysts, the authors demonstrated that over a few hours, carvacrol (and thymol) broke down the oocysts, as seen by a decrease in oocyst number and a corresponding increase in light absorbance (Figure 1).



Figure 1. Effect of carvacrol in vitro on Eimeria oocysts (adapted from Remmal et al. 2013)



An interesting observation when reviewing much of the literature investigating Eimeria challenge models and phytogenics, including oregano, is the use of mild challenge models. The Johnson and Reid system used to score intestinal coccidial lesion ranges from 1 to 4 for each Eimeria species; 1 refers to mild lesions increasing in severity to a score of 4. Many of the coccidial challenge models in the literature report scores in positive control birds (i.e. naïve birds that have been kept coccidia free and received no medication etc.) in the region of 1, indicating a mild challenge. This raises a question when these data are translated to the field situation: 'Do oregano-based products perform the same as in the laboratory when the Eimeria challenge is more severe?' After all, practical application in the commercial setting should be the end-point of such work to offer truly viable alternatives to current anticoccidial control programmes.


A recent study was conducted to investigate the performance of an oregano essential oil product (Orego-Stim) in broilers under simulated field conditions (reared on reused litter for 42 days) and a severe coccidial challenge. Birds received either Salinomycin (60 ppm), Orego-Stim (450 ppm), Anticoccidial vaccine (Coccivac B-52, Merck, USA) or a combination of Orego-Stim (150 ppm) and anticoccidial vaccine. A proportion of birds from each pen were transferred to cages at 21 days, challenged orally with mixed Eimeria species, killed and lesion scored 6 days later. Naïve, coccidia-free birds were also infected at 21 days to act as a positive control. Positive control birds recorded a mean lesion score of 3, indicating the birds had successfully received a severe coccidial challenge (Figure 2). Coccidial lesion scores were similar between Orego-Stim and Salinomycin, and significantly lower than challenged, untreated birds. Interestingly, concurrent use of Orego-Stim and anticoccidial vaccine did not interfere with coccidial protection afforded by the vaccine.


Figure 2. a) Coccidial lesion score reduction in birds challenged with mixed Eimeria species at 21 days




Figure 2. b) Litter oocyst counts in broilers given Salinomycin, Orego-Stim, Anticoccidial vaccine or Orego-Stim with anticoccidial vaccine. Columns with different letters are statistically significantly different (P < 0.05).



The study also demonstrated equivalent performance between birds given Salinomycin or Orego-Stim. Furthermore, performance of both Orego-Stim and Salinomycin was significantly improved, compared to coccidiosis-vaccinated birds. Moreover, concurrent use of Orego-Stim (150 ppm) and an anticoccidial vaccine conferred improved bird performance (Figure 3) compared to vaccine alone, without affecting immunity as demonstrated earlier (Figure 2).


Figure 3. Effect of Salinomycin, Orego-Stim, Anticoccidial vaccine or Orego-Stim with anticoccidial vaccine on weight gain in broilers. Columns with different letters are statistically significantly different    (P < 0.05).



Eimeria are ubiquitous in poultry production systems and consequently for the foreseeable future, coccidiosis management will be an integral part of poultry production. There are limited management tools available for the poultry farmer and while they are effective, they come with risks such as resistance development or potential performance losses. Phytogenics based on essential oils potentially offer another tool for coccidiosis management due to their broad range of beneficial properties. The interaction of oregano oil and Eimeria has been extensively studied and shows much promise for commercial application, yet a robust evaluation of their efficacy under field or simulated field conditions, is often lacking.


Recently, a commercial oregano oil product (Orego-Stim) was tested under commercial conditions. The results demonstrated that Orego-Stim positively influenced performance and lowered Eimeria lesion scores at similar levels to an ionophore, despite a severe coccidial challenge. This trial, as well as previously documented tests regarding the influence of oregano on gut health and immunity, suggest oregano essential oil products such as Orego-Stim could support coccidiosis management programmes, to help birds during periods of intestinal stress.


References available on request