For poultry producers to make a profit they must have healthy, uniform sized birds, make sure there are no real or assumed human health concerns that are associated with limiting antibiotic resistance, all while formulating diets on a least cost basis. Traditionally, antibiotics such as Ionophores (anticoccidial), bacitracin methylene disalicylate, tylosin phosphate and virginiamycin maintain healthy birds resulting in growth promotion and thus increased profit.
Even though Ionophorus antibiotics are not used in human medicine they are also grouped with all antibiotics. The ban of feeding antibiotics to broilers in EU, and the general increased awareness of consumers has increased the demand for “antibiotic free” poultry products. Thus, there is a need for optional products to antibiotics both in coccidiosis control and bacterial related to intestinal health. Some of these products are direct fed microbials, prebiotics (MOS), essential oils, saponin or sapogenines (yucca and/or quillaja), acidifers, and physically activated vitamin C combined with organic acids. Principally, the essential oils and saponins have demonstrated the most significant anticoccidial activity. As with the antibiotics, these products must work in today’s poultry production environment where feed prices are often high, alternative feed ingredients are routine, marginal coccidiosis control is common (drug resistance and or vaccination issues), heavily built-up litter is used, and the house environment highly variable. All of the afore-mentioned can lead to intestinal health issues, which must be managed by these products.
The goal of any anticoccidial program is to control severity of coccidiosis and also attempt to regulate when the primary damage will occur. The amount of damage is related to the species, amount, frequency and timing of exposure. Coccidiosis, even mild cases, has a negative impact on production with losses in feed conversion, weight gain, uniformity, pigmentation, and increased mortality. Coccidiosis continues to be the most frequently diagnosed disease in poultry. Almost all commercial poultry will become infected with coccidian; that’s some ~9 billon coccidia infected chickens each year in the USA. Coccidia are protozoan (Eimeria spp.) parasites that infect the intestine or ceca of poultry. The level and species of coccidia will vary with anticoccidial programs, management, and bird age.
Poultry coccidiosis is controlled by the use of prophylactic feeding of anticoccidial drugs (no Ionophorus antibiotics in antibiotic free production) or vaccinating with live coccidial vaccines. Drugs work directly on the coccidia. Degree of anticoccidial activity depends on efficacy and sensitivity, which vary greatly. Anticoccidials are broadly divided into synthetic (chemical) and ionophores.
In the US, currently the only approved non antibiotic anticoccidial drugs are: diclazuril, clopidol, amprolium, robenidine, zoalene, decoquinate, and nicarbazin. Both drug and vaccination programs also rely on immunity development. In order to predict coccidiosis control and immunity development, performance and related oocysts litter/fecal numbers are valuable tools. Eimeria are very immunogenic. With each cycle of coccidia in the host, immunological protection increases.
The development of self-limiting immunity, which eventually protects a flock, is a very critical objective for a coccidiosis control program, whether vaccination or an anticoccidial drug program. Fully sensitive chemical drugs limit oocysts shedding and related immunity development. The lack of full immunity once the chemical is removed influences subsequent degree and timing of coccidia development. Ionophores and partially resistant chemicals work similarly with partial direct control and regulated immunity development. Both of these traits allow some oocysts to be shed over the course of the growout with accompanying immunity development. Generally, oocysts shedding with this type program increases with a peak approximately d 28-35. However Chapman demonstrated that full immunity to most anticoccidial drugs take at least 6 to 7 wk.
The major concern with anticoccidial drugs is development of resistance. Resistance to some degree has developed to all drugs. Rotation and resting (not using for extended periods of time) slows resistance development. However with many of these drugs once resistance has developed it is very persistent/stable and years of non-use are needed to see a significant change. Anticoccidial sensitivity of coccidia isolated from poultry houses can be determined by anticoccidial sensitivity tests. ASTs are very useful in attempting to predict the control program that will have the most useful/sensitive drugs. Due to the increasing demand for antibiotic free birds and concerns of resistance issues with anticoccidial drugs, the use of coccidiosis vaccination has grown tremendously in the last few years.
The only method to produce a truly drug-free bird is through the use of coccidia vaccination. Vaccination programs use live oocysts, which are administered using a hatchery spray or gel, a gel puck placed into hatchery box, or in-ovo dosing. These methods provide a prescribed amount of oocysts at an early age enabling immunity development to progress rapidly but still at a desired rate. A significant amount of immunological protection develops by 14 d of age, allowing birds to withstand a substantial challenge by 21 to 28 d of age. Coccidial vaccines are of two types; non-attenuated (not altered) and attenuated.
All vaccines contain at least E. acervulina, E. maxima, and E. tenella. Non-attenuated vaccinated broilers’ oocysts shedding starts with an early d 7 peak, a major peak at d 18-28, and then a decline. Attenuation of the coccidia causes the attenuated vaccinated broilers to generally start oocysts shedding approximately a day earlier, with a lower oocysts shedding peak, and extends longer than non-attenuated vaccinated broilers. Many other factors influence oocysts shedding including management, duration of drug program, breed, vaccine condition and application. To sustain good coccidiosis management all programs and influences need to be considered. McDougald stated that for an anticoccidial to be effective for the broiler industry, it must have a broad spectrum of activity with a significant improvement in broiler performance. At the XIX World Poultry Congress, the author stated that the criteria for selection of an anticoccidial to use in a broiler complex should be based in the following: cost, efficacy/sensitivity, effect on acquired immunity, and toxicity.
Concentrating only on antibiotic free products, other than FDA approved anticoccidial drugs there are very few products that meet these criteria. Several have demonstrated ability to reduce oocysts production; generally this has not translated into reduction in coccidial lesions or improved performance. From research that I have conducted none of these products have demonstrated the anticoccidial activity of the fully sensitive FDA approved drugs. However due to demand for antibiotic free birds, drug resistance, toxicity, or tissue residue issues these products are an option. The two classes of products that have been tested showed the most promise as an anticoccidial are the saponin or sapogenines (isolated from yucca or quillaja) and the essential oils (single EOS or blends). In a series of coccidia challenge studies, a yucca sponnin product reduced E. acervulina, E. maxima, E. tenella, E. brunetti, and E. mitis compared to non-medicated infected controls. The strongest activity was against E. tenella.
One of the issues with coccidia vaccination is that it is a live product, which relies on immunity development thus birds are infected. Non-antibiotic products are often added to vaccination programs. Product, dose level, and timing of the addition are critical. In a coccidia challenge study with pure EO oregano with a low coccidia mixed species challenge demonstrated reduction in lesion scores. One of the criteria for a non-antibiotic product was to not interfere with coccidial immunity. A coccidia immunity study was conducted with this oregano product and coccidial vaccination. Oregano significantly reduced oocysts cycling and related coccidia immunity development. This information suggested that it was not appropriate to use this product in the starter feeds with a vaccine. Oregano product has been shown to work in the grower feed with vaccination after immunity has had a chance to develop. A proprietary mixture of organic minerals, yeast cell wall oligosaccharides and plant extracts has also been investigated. This product showed significant anticoccidial activity however not at a level to disrupt coccidial immunity development. Thus this product demonstrated advantageous benefits using continuously or only in the grower phase of a growout.
In discussing antibiotic free coccidiosis control we must also discuss enteric bacterial diseases. Coccidiosis coupled with associated enteric bacterial issues makes it the most costly disease facing the poultry industry. A survey of south-eastern USA poultry veterinarians ranked disease issues with coccidiosis as number one and necrotic enteritis as number two. Intestinal damage by coccidiosis or other stressors (nutritional, environmental, etc.) enables Clostridium perfringens to proliferate and potentially cause necrotic enteritis. The most direct necrotic enteritis link is between Clostridium perfringens and coccidiosis with E. maxima being the leading cause. In certain circumstances with vaccination or drug failure, the infection will cause significant damage to the intestine, which can lead to Clostridium perfringens proliferation and sub or clinical necrotic enteritis. The use of antibiotic placements now has a dual role reducing coccidiosis and necrotic enteritis.
References are available on request
Paper from 64th Western Poultry Disease Conference