Coccidiosis has long been a major disease facing poultry producers, with outbreaks significantly impacting bird health and performance. It remains one of the most economically significant diseases in poultry production, estimated to cost the UK industry in excess of £99 million per year (Blake et al., 2020).
Being a disease that is likely endemic on most poultry farms – whether that’s breeders, layers or broilers – it is important to recognise why the disease can have such an impact on flocks and how vets can support producers to proactively prevent the disease taking hold.
Coccidiosis – how big a problem is it?
Coccidiosis is a disease affecting the intestinal tract caused by a protozoan belonging to the genus Eimeria. Eimeria begin their lifecycle as unsporulated oocysts which are excreted in the litter. Once heat and moisture from the litter and air reaches these oocysts, they become sporulated and infective. At this stage, they are ingested by the bird. By the action of the gizzard and enzymes during digestion, sporozoites are released which then infect the intestinal cells.
Once sporozoites are inside the intestinal cells they start to multiply and, subsequently, burst. When this happens, they release merozoites to infect new cells. This happens by the merozoite entering the cell and differentiating into a macrogamont or microgamont which become a zygote when fused. The zygotes that are formed become the oocysts, which are then excreted back into the litter and go on to infect more birds. Infected birds excrete fresh oocysts into the environment days before any symptoms become apparent, enabling the disease to spread quickly throughout a flock.
Clinical signs of coccidiosis are mainly defined by the causative Eimeria
species. These can include blood in the faeces, weight loss and visibly sick birds. Damage to the cells of a chicken’s intestinal tract caused by coccidiosis results in increased mortality, poor utilisation of feed, impaired growth and poor flock uniformity. A damaged gut also opens the gateway for other poultry diseases.
Favourable conditions for coccidial infections
For oocysts to become infective, sporulation is necessary and this requires moisture, at around 60 percent relative humidity, and temperatures of around 22°C to 28°C. If an oocyst hasn’t sporulated within a week, it will die.
Unfortunately, typical UK poultry sites are perfect conditions for coccidial infections, with high stocking densities providing the ideal opportunity for coccidia to multiply. High humidity levels and litter moisture also help oocysts sporulate and become infective.
Poultry houses are naturally warm with moisture provided by birds themselves when they excrete and during respiration. The highest moisture will be at the feed and water lines, and possibly along the side walls of the sheds where there may be condensation and ground moisture.
Vaccination as a method of control
In the layer and breeder sectors, vaccination is the most common method of control. Vaccines are designed to induce immunity safely and as quickly as possible when administered properly. For this method to be effective, live sporulated oocysts must be ingested to establish low-level infection and induce immunity. These are shed from around four days post-vaccine.
One of the benefits of coccidiosis vaccines is that they are “self-boosting”, meaning they recycle under the correct field conditions.
It’s important to note that the strains of coccidia which the vaccines contain have shortened life cycles. This means that fewer asexual reproductive stages occur before they are excreted by the bird and they therefore do not damage the bird’s intestinal tissue.
Once birds are vaccinated with a coccidial vaccine, it is vital that they continue to have access to their droppings as this is where, under favourable temperature and humidity conditions, the oocyst sporulates to become infective.
Vets should also advise producers that if relative humidity doesn’t rise above 60 percent under normal brooding conditions, consideration should be given to spraying the internal walls of the building or the litter with water to achieve this relative humidity.
Application techniques for vaccination
When applying a coccidial vaccine, the main challenge is ensuring all birds receive a full dose. If this is not achieved, the flock will eventually develop immunity, but it will take longer for every bird to complete the cycles required. This will mean that the less protected birds in the flock will be more susceptible to challenge, and flock weight and uniformity can suffer.
When advising producers on vaccination application, there are two options to consider: vaccination in the hatchery or on-farm.
The main benefit of hatchery application is that chicks will receive the vaccine as early in life as possible, encouraging early immunity. It can also be an easy option for producers saving on time and labour. Vaccinations in the hatchery are usually applied as a course spray, combined with either water or a specific solvent, and the chicks ingest the vaccine through preening.
If producers are applying the vaccine on-farm, spray tends to be the most popular choice. If possible, encourage producers to keep the chicks in the chick boxes on arrival, as this means it is easier to ensure they all receive an adequate vaccination dose via the knapsack sprayer. Again, this can be used with either water or solvent.
Alternatively, producers can choose to vaccinate chicks via drinking water. In this instance, it’s recommended to start the process from three days of age, adding supplementary drinkers so that all chicks have access, and using a dye in the water to help monitor uptake.
The vaccine can also be applied via spray straight onto the feed on the day the birds arrive on-farm.
Top tips when using coccidiosis vaccines on-farm
Ensuring vaccines are stored and administered correctly can greatly affect their efficacy, so there are a few important things to remind producers of:
- Prepare in advance – once they’ve selected the vaccine they wish to use, make sure it is ordered in plenty of time before the chicks arrive. This means that the vaccine can be administered as soon as they arrive on-farm
- Storage – making sure vaccinations are stored at the correct fridge temperature is absolutely vital. Otherwise, you run the risk of the vaccine becoming ineffective. Remind producers to place a thermometer inside the fridge to keep an accurate record of temperatures and look at the product data sheet to verify temperature requirements
- Shake the vaccine bag well before use – this will ensure the oocysts do not settle out of suspension
- Sprayer calibration – if producers are using a sprayer, ensure this is calibrated and producers have calculated how many seconds they will need to spray each basket to achieve even coverage
- Using a dye or coloured solvent – the addition of the colour means it is easy to see where vaccine has been sprayed to ensure even coverage
- Lighting – when vaccines are applied by spray, chicks must preen one another to ingest the vaccine. Therefore, keeping lighting bright up to 15 minutes after the application will mean they are more active and more likely to ingest the vaccine at this time
- Oocyst per gram (OPG) counts and specification – these are a good tool for vets to offer producers to monitor how well the vaccine is cycling within a flock
Vaccination efficacy can be measured through OPG counts together with oocyst specification. Using this method enables you to help producers identify how many oocysts they’ve got in droppings as well as what type of oocysts are present.
Sampling is generally recommended no earlier than 10 days post-vaccination, though oocyst shedding begins five days after vaccination.
Producers will often routinely vaccinate for coccidiosis, so it is worth recommending that they carry out occasional monitoring to check the process is still being carried out correctly. By giving them simple tips on correct application, overall vaccine uptake and flock immunity can be greatly improved.