In Ovo Chicken Vaccination: How Does It Work?
Vaccination is an extremely important part of healthcare for animals and humans alike. Across the world, many dangerous diseases are managed, prevented, controlled, or even eradicated by vaccines. In chickens, vaccines are available for a number of different viruses, bacteria, and fungal infections. While chicks can have them after hatching, another method is through in ovo, or in-egg, vaccination.
Poultry Diseases and Vaccines
Generally speaking, all large-scale commercial chickens receive vaccines. Which vaccines they get usually depends on their location. This is because some diseases are much more prevalent in different parts of the world. For example, fowlpox is a disease which causes warts to form on the combs and wattles of chickens. As it is common in Asia, chickens there usually receive vaccinations. In Europe, it is much less of a problem, so not all birds get the vaccine. Some diseases, like Newcastle disease, are so virulent and potentially devastating, that the majority of chickens receive the vaccine.
Vaccines can be live, where the pathogen is still intact, or killed, where the pathogen has been inactivated. In a live vaccine the chicken receives a small amount of antigen. This is often in the form of an intact, but attenuated, pathogen – one with artificially decreased virulence – or a much less pathogenic strain. A very famous example that illustrates this principle is the very first vaccine. In 1796, Edward Jenner found that infection with the relatively mild cowpox prevented people from catching the deadly smallpox. Intentional infection with cowpox became a popular natural vaccine until the 20th century when the modern smallpox vaccine emerged.
Vaccination programmes give animals as much protection as possible and prevent and or reduce losses from disease. While there are lots of different methods of vaccine administration in chickens – from sprays, to injections, to eye drops – in ovo vaccination is both fascinating and highly efficient.
In Ovo Vaccination
The idea of in ovo vaccination is that a developing chick receives a vaccine before hatching. This removes a lot of the stress from handling that day-old chicks go through when getting vaccines through other routes. At the same time, it provides an early start to immunity and promotes healthy growth. The machine punctures the eggshell with a fine needle and carefully injects the vaccine. Needle placement is usually automatic, as this prevents the damage to the embryo. While not all important chicken vaccines are available in this form, there are some that are now routine across large areas of the world.
The technology was initially developed in the 1990s and was only really applicable on a large scale. In ovo setups were big, expensive, and capable of processing 35,000 – 70,000 eggs per hour. More recently, smaller setups have been developed which are more economical for small hatcheries. As a result, in ovo vaccination is becoming more widespread and is now used regularly in large and small hatcheries.
How In Ovo Vaccination Works
The vaccination equipment pierces a small hole in the egg. The needle goes through this hole and into either the amniotic fluid around the developing embryo, or into the embryo itself. If the vaccine is injected anywhere else, it is less likely to provide full protection. One the vaccine is in the egg, the chick’s immune system will respond.
While there are some risks that come from in ovo vaccination, hatchability of eggs does not tend to decrease after vaccination. Usually, chicks will only be less likely to hatch if the injection is in the wrong place. This can be an issue if the vaccination badly timed. Many in ovo machines, however are able to identify where the embryo is in the egg to ensure correct needle placement.
The other risk from this kind of vaccination is the transfer of bacteria between eggs. As the machine tend to treat thousands of eggs in short periods of time, ensuring there is no contamination of the needles is paramount. If a needle enters an unviable or even a rotten egg, this can then transfer disease and infection to other eggs. As such, many hatcheries candle eggs before vaccination to make sure that there is a viable embryo inside.
The Ups and Downs
In ovo vaccination has many benefits:
- Reduces stress on young chicks
- Allows early development of immunity
- Removes user error in vaccination
- Saves time and is less labour intensive than other vaccination methods
- Is easy to integrate with other automation e.g. candling
However, there are some barriers to its widespread use:
- Technology is initially expensive
- Requires skilled operators and strict biosecurity measures
- Not all important chicken diseases have an in ovo vaccine
- Might not be economically viable if hatcheries are small
- Incorrect timing or needle placement can damage embryos
Which Vaccines Are Available?
Initially, the vaccine for Marek’s disease was the primary in ovo vaccine candidate. This disease is extremely infectious and can cause mortality up to 50% in an unvaccinated flock. As this disease was rare in the UK, this was one of the reasons that in ovo technology did not take off there. In recent years, Marek’s disease has become more widespread and now vaccination is common across Europe.
Vaccines for Infectious bursal disease, infectious laryngotracheitis, poxvirus, Newcastle disease, Avian influenza and coccidiosis are now common in in ovo vaccination programmes. There are also other vaccines which show promise in a lab setting, such as those for haemorrhagic enteritis and against Campylobacter bacteria. However, these need validation before they can be commercially available.
- Ricks, et al. (1999) Advances in Veterinary Medicine, 41, 495-515.
- Schijns (2014) Avian Immunology | Practical Aspects of Poultry Vaccination. 345–362.
- Stone, Mitchell & Brugh (1997) Avian Dis., 4 856-63.