Coccidiosis is thought to cost the poultry industry US$3 billion worldwide each year, making it the most costly disease to affect poultry producers around the world. Consequently, achieving thorough and consistent protection against the disease should not be underestimated.
Coccidiosis vaccination in the hatchery using the spray method has long been judged as a a convenient and successful method to vaccinate chicks, with coccidiosis vaccines applied to day-old chicks (DOCs) using standard cabinets which have been set up to maximize droplet size.
Hitting the target?
Once the vaccine is sprayed over the chicks, they become quite wet and start pipping and rubbing against each other. This brings the vaccine into contact with the upper digestive and mucosal tissue including the eyes, nostril and mouth.
Yet, despite its widespread adoption, this method of vaccination has several limitations and drawbacks.
For example, there can be a lot of waste as the vaccine quickly dries on application, and a high proportion of the vaccine often is administered in small droplets that are not big enough to be pipped by the chicks.
Additionally, a large amount of vaccine is wasted on the chicks’ feathers and the crate floor. Should the vaccine be unevenly distributed, then take will be similarly uneven. Wet chicks also can experience a significant drop in body temperature after spraying.
So despite the widespread use of vaccination, it has its limitations. Gel vaccination, however, can eliminate many of the problems traditionally associated with spray approach.
Dangers of poor coverage
The objective of any coccidiosis vaccination method should be to allocate the correct dose of vaccine strains of one or more Eimeria species into the digestive tract of the chick. The target should be the gut – and not the feathers, nostrils or eyes – and only by targeting the gut can vaccination be optimal. Applying vaccine by gel can raise the number of effective vaccine droplets pipped and ingested by chicks by 30 percent compared with spray droplets.
As infection and immunity are cyclical, so is the immunity triggered by coccidiosis vaccines. Infection, by wild or vaccine strains, is followed by replication inside the bird and immunity builds up. Seeding of new oocysts occurs in the litter via the feces, and re-infection occurs in a continuous cycle.
Depending on the type or combination of Eimeria sp included in a vaccine – E acervulina, E brunette, E maxima, E tenella, E necatrix – it can be concluded that first shedding of the vaccine oocysts will occur between Day 6 and Day 9 following vaccination - or first cycle. Consequently, any birds that were missed during vaccination will be infected as part of the first cycle around a week later.
However, the amount of excreted oocysts in the feces in the first cycle is much higher than in the vaccine dose, approximately 140 times higher, and so the impact of the infection on non-vaccinated birds will be much higher.
The number of excreted oocysts will increase with each cycle; for example during the second and third cycles, the number will be around 2,100, and 4,300 times higher.
It is this repeating cycle that infects any birds missed during hatchery vaccination. In other words, a large percentage of DOCs not correctly vaccinated at the hatchery due to inefficient spray application will more than likely be later infected by a larger amount of excreted oocysts once on the farm, and be exposed to a high risk of severe reaction and intestinal necrosis.
Because of this, achieving 100 percent vaccine coverage in the hatchery at Day 1 is key to achieving homogeneous and consistent immunity throughout the life of the birds, and gel application has been shown to achieve greater DOC coverage when compared to spray vaccination.
Spray vs. gel droplet
Another important aspect to consider is the volume of vaccine ingested, and it is essential to differentiate the number of chicks receiving the correct, full dose of vaccine delivered to the intestinal tract from those receiving an insufficient amount, or no vaccine at all.
A critical amount of vaccine oocysts is needed to ensure correct replication in the gut and so achieve the first successful cycle of development in the bird. It is also important to remember that spray vaccination does not normally guarantee a constant and sufficient amount of vaccine intake on application, because of waste, droplet size limitations, and poor homogeneity in the spray pattern.
The droplet size with gel vaccination, however, is constant, and due to the viscosity and homogeneity of the gel, droplets remain adhered to the birds’ feathers and do not fall to the crate floor. The quantity wasted is almost negligible.
Birds can easily preen the droplets, and this results in a full dose of vaccine being delivered to the target – the gut. In this way, the number of birds receiving an insufficient dose in minimized. The standard volume of each droplet helps to ensure good vaccine distribution throughout the crate, contributing to a more effective rate of vaccine take by all the chicks.
Of course, there are several alternatives to spray and gel when considering vaccination, for example, administration via drinking.
However, this approach tends to be less than optimal in achieving protection against coccidiosis, due to factors such as water quality, chick management, early exposure to the litter/field oocysts in addition to the vaccine oocysts, uneven distribution of the vaccine in the waterpipes, and stress.
Another method of coccidiosis vaccine is the gel puck. While this delivers vaccine directly to the gut, achieving homogeneity can be poor. It can also be the case that some crated chicks will not be able to reach the puck and so get no vaccine at all.
In ovo vaccination can also be used for coccidiosis control, however, there is some controversy around this method. In theory, delivering a large amount of oocysts into the amniontic fluid via injection will ensure that a critical number reach the gut by the time the embryo swallows the amniotic fluid, which occurs immediately before internal pipping at 19.2 days of development.
However, this technique can be problematic if, for example, in ovo vaccination occurs intra-muscularly, subcutaneously or in the allantois. Depending on the age of the flock, egg size, type of equipment, incubation tray and injection timing, these types of incorrect vaccine application can be as high as 85 percent of the total.
Gel application for coccidiosis vaccination offers even, homogeneous dosing and take per bird is higher than other methods. It also significantly reduces the number of chicks missing Day 1 vaccination and experiencing vaccine infection after the first cycle on the farm. In addition, the amount of vaccine wasted is practically nil, and it has the further benefit of not wetting DOCs post hatch.