The severity of infection will depend mainly upon the number of infective oocysts ingested i.e. on the infection pressure in the poultry house.
Birds suffering from clinical coccidiosis will show typical signs like diarrhea, bloody droppings, increased mortality, decreased feed intake and impaired performance. Insufficient control of coccidiosis also leads to impaired growth and feed conversion ratio, without the presence of evident clinical signs, so called subclinical coccidiosis or coccidiasis.
Intensive methods of production of poultry greatly favor the reproduction of Eimeria. As a consequence, coccidiosis is a continuing problem requiring constant attention and, in the case of broilers, a need for continuous supplementation with anticoccidial drugs or coccidiosis vaccines. The latter is becoming more important in recent years as it can be an alternative to manage coccidiosis and it can restore sensitivity of the Eimeria species in case of decreased efficacy of the current registerd anticoccidials.
The prevalence of clinical coccidiosis is estimated at 5% and of subclinical coccidiosis at 20% of global poultry production. This demonstrates that under current production systems, coccidiosis is still a major issue.
Coccidiosis control by means of vaccination is standard practice in breeder and layer flocks housed in alternative systems. For vaccination live vaccines are being used, resulting in controlled contact, with minimal intestinal damage, with the different Eimeria species at an early age of life; the contact being necessary to establish immunity against the pathogenic field strains.
The reasons to consider coccidiosis vaccination in broilers (at least those slaughtered at younger ages, 6 weeks of age) are different. The main reasons for vaccination in these broilers is not for immunity build-up, but for improvement of the sensitivity of the Eimeria field strains to anticoccidial compounds, the so called 'restoration of sensitivity' concept.
Furthermore, changing demands of retailers for specific labels, like antibiotic free (ABF) and no antibiotics ever (NAE) policies are, especially in the US, drivers for the increased use of coccidiosis vaccines in broiler flocks.
The success of coccidiosis vaccination is influenced by two important parameters:
- the intake of the vaccine immediately after vaccination
- the consecutive cycling of the vaccine
Firstly, special attention must be paid to vaccine application. In most cases, coccidiosis vaccine administrations are mass applications by spraying the vaccine on the birds (in the hatchery or at arrival in the poultry house), spraying on the feed or by adding it to the drinking water. Although individual application of coccidiosis vaccines (for instance by eye drop) is the golden standard for guaranteeing the correct dosing for each individual bird, it is rarely performed because it is very labor intensive.
Mass application, if not applied properly, might result in incomplete vaccination of a part of the population as not every bird will swallow equal amounts of the vaccine. Coccidiosis vaccination in the hatchery using the spray method has long been judged as a convenient and successful method to vaccinate chicks, with coccidiosis vaccines applied to day-old chicks using standard cabinets which have been set up to maximize droplet size.
In order to optimize the chances of good coccidiosis control, it is important to take notice of some specific guidelines during the application and in the management of the farm.
Seven critical steps of good coccidiosis vaccination
Correct application in the hatchery:
A coccidiosis vaccine contains live parasites and transport and storage of the vaccine should be temperature controlled. A coccidiosis vaccine is sensitive to temperature variation. The optimal temperature for transporting and storage of the vaccines is between 2o and 8o Celsius. It is advisable to monitor temperatures during transport and storage and any abnormalities should be reported. Extra care should be taken to ensure the vaccine is never frozen in transport or storage as freezing oocysts will kill them. Check for cold spots in the refrigerator.
2. Vaccine preparation
The dilution should always be made according to the specifications of the manufacturer for a specific vaccine. Preferably distilled water should be used as chlorinated water might have a negative effect on the viability of the parasite. In order to remove all the oocysts from the vial, the vial should be rinsed at least 2-3 times. Next to diluting the vaccine with water, a dye is added to the solution. The reason for adding a dye is to make the droplets more visible to the chicks and promote preening and in this way the intake of the vaccine. The dye should be diluted according to the manufacturer specifications.
Use a clean spraying vaccine device which provides a droplet size of ≥100μm/ In spraying devices containing a filter it is advised to remove the filter during vaccination. Once the vaccine solution is prepared it must be constantly mixed. Oocysts are heavier than water so they would sink to the bottom if not constantly kept moving (stirring can be done by means of air or a magnetic rod). It is very important that the oocysts are evenly distributed in the solution to ensure that each bird is vaccinated with the same dosage. When the chick crates pass the nozzles of the spray cabinet, the distribution of the spray should be carefully adjusted so that it covers the entire box (not too much or too little). This should be tested and adjusted before the first batch of birds pass through the spraying machine.
The volume for spraying one box of 100 chicks is usually around 25 ml. The dilution of the vaccine is calculated based on the number of chicks inside one box, the flow rate and the package of the vaccine. For example for boxes containing 100 chicks, a vaccine vial of 10,000 doses should be diluted in 2.5 liters of water, if the spray cabinet is spraying 25 ml per box. This should be checked before and during application and adjusted when needed.
The spray should be coarse meaning that the chicks need to see the droplets. When a mist is created, the droplet size is set too small and the birds will be less stimulated to start preening. A coccidiosis vaccine is intended to be ingested and not inhaled. Important to note is that an unsprayed chick does not necessarily mean that it is not vaccinated. As described below, preening is essential for vaccine uptake.
This is essentially the most important part of the vaccination as the chicks will actually be vaccinated by ingestion of droplets (= preening). When the box passes under the nozzles the birds get wet and colored (in the case of using a dye). It is not because a chick has droplets on its head that it is vaccinated. The real vaccination is obtained when they ingest the droplets from another chick in the crate. It is important to have sufficient light after the vaccination to encourage preening. Ideally, this light should not only come from the ceiling but also from sideways.
If crates are stacked too high, the lower boxes might not get enough light and the birds will not be stimulated enough to preen. Correct temperature between 24o and 27o Celsius without draft in the waiting room is also important to have sufficient activity for preening. Attention should be paid that the birds are completely dry before they get transported so it is recommended to have at least a time span of 15-20 minutes before loading the crates.
Coccidiosis vaccines are live vaccines and, in order to obtain a solid immunity, each of the different Eimeria species in the vaccine need to replicate. Eimeria replication takes place in specific regions in the intestine for each species. At the end of the replication, new vaccine parasites are excreted and when these are again picked up by the chickens, a second wave of vaccine replication will start.
It has been demonstrated that a second and even a third contact with replicating parasites is necessary to obtain a solid immunity. This indicates the importance of the Eimeria species in the vaccine to be capable of multiplying themselves.
In order to allow this cycling of the vaccine, certain measures on the farm are advisable:
5. Preparation of the poultry house
Before entering new birds in the house is should be thoroughly prepared. Special attention should be given to the feeding and drinking lines. It should be carefully checked that no feed is left in the feeders and the silos from the previous flock as this might contain medication and/or anticoccidials that might interfere with the vaccine.
It is paramount for the success of a coccidiosis vaccination not to have any kind of drugs in the feed that could kill the vaccine. The same applies for the drinking water. This is especially important in the first weeks after vaccination until solid immunity has been developed. Next to this, if vaccination is done alternately with anticoccidials between flocks, one can optimize vaccination by doing a cleanup (with chemical anticoccidial) the flock before as this will lower the coccidiosis infection pressure considerably, giving an advantage to the vaccine strains to dominate the poultry house.
Both temperature and humidity are very important parameters for the cycling of the vaccine. Next to the general advise for good brooding management (CO2: <2,000ppm, maximum 3,000ppm; NH3: <10ppm, minimum 32oC at chicken height; ideal floor temperature of 30oC; warm the house before placing the litter) there are specific requirements when coccidiosis vaccination is applied.
For optimal sporulation of oocysts a relative humidity in the house of 60%, a dry matter content in the litter of maximum 80% and a litter temperature of at least 25% is advisable. For cycling of oocysts contact between excreted vaccine and the birds if necessary. This is guaranteed if broilers are floor reared and under normal commercial density.
It is advisable to monitor the flock after vaccination. This can be done by performing necropsies or by doing OPG counts. It is expected to have high OPG counts after vaccination as this is crucial to allow the vaccines to cycle. As for necropsies, the ideal age of the birds to check for coccidiosis lesion would be between 15 days of age until slaughter age.
It can be expected to see some cocciodiosis lesions as the birds received the parasite but the scores should not be too high and they should disappear early (earlier than normal) as the vaccine strains have a shorter life cycle and will induce lower lesions. Monitoring should be done regularly and any deviation reported to the manufacturer.
Coccidiosis vaccination in broilers is becoming increasinly popular. Crucial for successful vaccination is a correct application and management afterwards to allow cycling of the vaccine.
This article originally appeared in International Hatchery Practice, Volume 32 Number 6.