Potential exposure to a wider range of avian diseases means that free-range chickens need to have more vaccinations than colony birds to protect them during the lay period.

“Traditionally, laying hens were always kept as free range in backyards,” says Helen Houghton, avian manager for Merial Animal Health. “But then, as flock sizes grew in the 1950s, hens started to be kept in cages for ease of management, and benefits to bird health were seen as they were exposed to less disease.

“No one can disagree that the sight of free-range chickens enjoying being outside on grass is a great advert for our industry,” she adds. “However, these birds need to be carefully managed and protected from the disease risks that they can face.”

Free-range hens are vaccinated “in rear” to help protect them against disease challenges that they may come across, and also to protect against diseases of human health significance such as salmonella.

Most vaccinations that pullets receive are live vaccines, administered by spray or drinking water. But there are some vaccinations that have to be given by injection.

Depending on the disease challenge on the laying site, birds can be vaccinated against erysipelas, Pasteurella multocida and E coli. Pullets will need two vaccinations four weeks apart to protect them, starting at 12 weeks of age.

Virtually all pullets will also receive a combination vaccine to protect against infectious bronchitis and Egg Drop Syndrome, Newcastle disease and avian rhinotracheitis at 16 weeks, to help maintain health, good egg quality and production.

Muscle mass

“The problem you have with 12-week-old pullets is they’re small birds with very little muscle mass,” says Mrs Houghton. “They all have to be handled for inactivated vaccines as they must be injected.

“The pullets will also receive vaccinations at 16 weeks as they are being moved to their laying sites. The additional vaccines that pullets destined for some free-range sites require can mean more stress on the birds and can be a challenge for the pullet rearer to administer.”

Traditionally in the UK, pullets always used to be injected in the leg muscles. But this carries the risk of hitting nerves and joints, causing physical damage leading to lameness.

The pullets can also react to the oil-based vaccines themselves and this can cause lameness, if the vaccine is not injected properly into the muscle. As a result, instead of looking for food and water, they sit in one place and lose weight – leading to unevenness in the flock.

Even if there is a reaction to the vaccine following a breast injection, the chicken often still manages to eat and drink.

Liver puncture

Accurate placing of the needle into the breast muscle is critical, Mrs Houghton adds, as incorrect placement can lead to liver puncture. She says a ¼in, 19-gauge needle is best-suited and should be changed at least every bottle of vaccine in order to avoid spread of contaminants.

Merial provides stereo equipment in the form of Socorex guns, which help to speed up the process as two vaccinations can be given at the same time into two injection sites.

“Catchers should present the birds to the vaccinators with a maximum of three birds in each hand. The birds should be placed flat on a trestle table, breast side up, with the chicken’s head pointing towards the vaccinator. Catchers should hold both the bird’s legs at all times.

“To find the ideal injection site, the vaccinator’s thumb can be lightly placed in the throat area of the bird next to the crop. Vaccine should be injected into the deepest part of the breast muscle, parallel with either side of the vaccinator’s thumb on the triangle between the cranial point of the keel and the shoulder joint.”

The needle needs to go in parallel to the muscle as opposed to injecting perpendicularly, as this can result in penetration through the keel into the chest. If you go in too low, it can pierce the liver.