Behavior in the Field of Coccidia Vaccine (ADVENT) in Broiler Chickens during 2010 in USA

Avian coccidiosis is a common parasitic disease of broiler chickens caused by single protozoan parasite of the genus Eimeria that infect the intestinal tract and is transmitted among the birds via ingestion of infective oocysts during feeding. Coccidiosis cause a substantial economic cost to the poultry industry that is calculated on more that $800 million in annual losses (9). Losses are attributed to feed medication for prevention and treatment, mortality, malabsorption, inefficient feed utilization, and impaired growth rate. There are two types of coccidiosis, a clinical coccidiosis in which the birds affected show typical symptoms of the disease and a subclinical coccidiosis in which the affected birds do not show any visible symptoms of the disease. In the Annual Report of the United States Animal Health Report for 2010 Coccidiosis was ranking number four out of nine of the diseases that are concern for the poultry industry. In the report, the Association of Veterinarians in Broiler Production comment: "Coccidiosis always remains a concern for the broiler industry. The clinical and subclinical disease costs the industry a tremendous amount of money. Over the past several years, the industry's use of coccidia vaccines has increased due mostly to side effects associated with ionophores". Coccidiosis oocysts are extremely resistant to environmental conditions and disinfectant agents. In broiler chickens, coccidiosis prevention and control has been achieved since the 1950's by the use of two main tools, anticoccidial agents through the feed (2) and live vaccines either attenuated or non-attenuated live oocysts (5). Both methods of prevention and control rely on immunity development. The use of anticoccidial drugs chemical and ionophore in shuttle or rotation programs with each production cycle have extended the life of many of these drugs. However, numerous reports have showed a reduced of sensitivity and resistant to all-in feed anticoccidial drugs used in the poultry industry. Through a very extensive usage, increased demand for natural and organic chicken products, lack of new anticoccidial drugs and increased in the incidence of gangrenous dermatitis, the use of coccidiosis vaccines for control is now common in the USA.

In the United States there are today four commercially coccidiosis vaccines available for the prevention and control of coccidiosis in broiler flocks. ADVENT® is a coccidiosis vaccine that contains sporulated viable oocyst from three commercially relevant species in broilers, E. acervulina (strain VND-A10), E. maxima (strain VNDM27), and E. tenella (strain LPRL-49) suspended on a Phosphate Buffer Solution. The strains have been selected to have the robust protection necessary, broad immunogenicity and undiminished oocyst yield for today's broiler production. An in vitro potency method (VIACYST® Assay) is used to determine the viability of sporocysts of each of the three Eimeria strains that allow accurate and consistent vaccine formulation.

As long as broiler chickens are continued to be raised in confinement under current production systems the prevention and control methods available today must be optimized in order to minimize the negative impact of coccidiosis either clinical or subclinical on broiler performance. Coccidiosis vaccines are an effective tool to prevent and control the disease whether is used year round or either in a rotation program with in-feed anticoccidial drugs in the modern poultry industry. 

Coccidiosis prevention and control have been relied on the use of synthetic anticoccidial (chemicals) since the 1950's, but very frequently significant resistance would develop relatively quickly, except in the case of a chemical anticoccidial compound (Nicarbazin) that was introduced in 1955 and it remains a regularly used and effective medication for the prevention and control of coccidiosis. In 1972, the first polyether ionophore anticoccidial was introduced in the prevention and control through feed medication. Since them the used of ionophores have become the most widely used anticoccidial drugs for coccidiosis control in broiler chickens. However, recent reports have showed the increased of the prevalence of resistant strains of Eimeria to anticoccidial drugs. Mathis showed that the level of sensitivity to two ionophores (Monensin, Salinomycin) of an isolate that has never been exposed to any drugs compared to a 2009 commercial field isolates result in decreased of the effectiveness in the control of coccidiosis. Other studies that examined the sensitivity of isolates of E. acervulina, E. maxima and E. tenella to Narasin and Lasolacid found that the drugs were only marginally or poorly effective (1, 6).

The use of coccidiosis vaccine as part of a rotational coccidiosis control program decreased the resistance to the ionophore and chemical drugs in the program and extends their usefulness (2, 7). Coccidiosis vaccines also populate the litter with drug sensitive oocysts and a positive effect in broiler performance boost can be observed when flocks received anticoccidial agents after coccidiosis vaccine is used in the flocks (10). In a study at the Stephen F. Austin State University, ADVENT® coccidiosis vaccine was used in five consecutive flocks on a commercial broiler farm and was compared to a chemical/ionophore coccidiostat program. The results showed an improvement in performance in the subsequent two flocks were the ADVENT® coccidiosis vaccine was used (3). The use of coccidiosis vaccine also reduces the incidence of gangrenous dermatitis when is used to replace ionophores during certain period of the year (8).

One way to monitor a subclinical coccidiosis which is more difficult to diagnose and treat because the affected flock appears normal is by holding a regular basis "posting sessions" every 5-8 weeks, in which a representative sample of birds (5-6 birds/house or farm) from a variety of poultry farms and ages are examined for the presence of subclinical diseases. One of the main objectives of the posting sessions is to evaluated coccidiosis or the mortality for typical lesions cause by coccidiosis. In 1970, a method for scoring coccidial lesions was developed to intend achieve uniformity of lesion scoring among coccidiosis researchers (4). Since them the system has been widely adopted by veterinarians, parasitologists, and poultry health professional to examining coccidiosis lesions in broiler chickens. The method consists in recording macroscopic lesions and scrapings taking from the gut from all the birds for microscopic evaluation. Severity of the lesions is scored on scale ranging from 0 (no visible lesions to +4 (very severe lesions). Based on Johnson ad Reid method ADVENT® coccidiosis vaccine was evaluated during 2010. A total of 2000 broiler chickens were evaluated among the ADVENT® customer users. Broiler chickens that were evaluated included flocks from the three bird sizes (small = 3.6-4.4 lbs, middle = 5.2-6.0 lbs, large = >7.5 lbs) common raised in the USA, antibiotic drug free birds and organic birds. Results from the coccidiosis broiler evaluation will be presented.

Coccidial vaccines will not eliminate coccidiosis forever but they are an effective tool to prevent and control the disease in combination with anticoccidial drugs as an integrated program designed to achieve success and sustainable coccidiosis control in the modern poultry industry. 

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