Vaccination plays an important part in the health management of the poultry flock. There are numerous diseases that are prevented by vaccinating the birds against them. A vaccine helps to prevent a particular disease by triggering or boosting the bird’s immune system to produce antibodies that in turn fight the invading causal organisms.
A natural invasion that actually causes the disease will have the same result as the bird will produce antibodies that fight the current invasion as well as to prevent future invasions by the same causal organisms. Unfortunately, birds that become diseased usually become unthrifty, non-productive or even die. An infection caused by natural invasion will be uncontrolled and therefore has the possibility of causing severe damage, however, vaccination provides a way of controlling the result with minimal harm to the birds.
Vaccines are generally fragile products, some of which are live but in a state of suspended animation. Others are dead. All have a finite life that is governed by the way they are handled and used. Handling and administration procedures also influence the potency of many vaccines and consequently the level of immunity the bird develops.
Live vaccine – the active part of the vaccine is the live organism that causes the disease. As such, it is capable of inducing the disease in birds that have not had previous contact that organism. Vaccinated birds, in many cases, are able to infect non-vaccinated birds if housed together.
Attenuated vaccine – with this type of vaccine the organism has been weakened by special procedures during manufacture so that it has lost its ability to cause the serious form of the disease. At worst, the birds may contract a very mild form of the disease, however, the vaccine still has the ability to trigger the immune system to produce antibodies.
Killed vaccine – with this type of vaccine the organism has been killed and is unable to cause the disease, although the ability to trigger the immune system remains. In many cases, the level of immunity produced by this form of vaccine is weaker than that produced by live and attenuated vaccines.
Vaccines are produced mainly in three forms:
Vaccines are sold in dose lots, the number of doses being the number of fowls that may be vaccinated with that amount of vaccine when using the recommended technique. In the case of many vaccines, there are differences in the disease organism strains that they are effective against. It is important that the correct vaccine strain be used and this can only be determined by veterinary advice.
Vaccines are fragile in many respects and require very careful handling to ensure they retain their potency. Poor handling procedures will, in most cases, result in a rapid decline of potency.
The important handling requirements on the farm are:
On receipt of the vaccine on the farm, check and record:
There are a number of ways that vaccines may be administered to poultry and it is very important that the correct method is used for each vaccine. To use the wrong method will often result in failure of the vaccine to produce the desired immunity. Some of the methods require the operator to handle every bird and, consequently are time consuming and stressful to the birds and operator. Other methods involve administration by methods much less stressful and time consuming. These methods include administration via the drinking water or as an aerosol spray. The different ways that the vaccines may be administered to poultry are below.
Using the method of in-ovo vaccination, the vaccine is administered into the embryo before hatch.
In general, vaccines can be applied to five different areas of the egg: the air cell, the allantoic sac, the amniotic fluid, the body of the embryo and the yolk sac. Vaccine uptake and therefore the immune response of the chicken depends largely on the area of injection. While injection in the air cell has been shown to be minor/not effective, injection in the body of the embryo or the allantoic sac is effective. Therefore, the optimum period to inject the embryo is in the late stage of development, i.e. the time between the ascendance of the stalk of the yolk sac into the abdomen (about the time when the chicken tucks its head under its wings) and external pipping.
During that late stage of development, the embryo is mature enough to cope with the viral stimulus and the trauma induced by the penetrating needle is unlikely to cause severe tissue damage. Signs of too early vaccination include reduced hatchability, late death and increased number of culled birds. However, if vaccination is done too late in embryonation, the risk of eggshell breakage is significantly higher. Therefore, in ovo vaccination is commonly performed between days 18-19 of incubation.
The system of a larger outer needle (penetrating the eggshell) that contains an inner needle (penetrating the embryo) enables for strong but careful penetration of the egg and minimizes trauma to the embryo. In addition, the use of two needles reduces the likelihood of transferring contaminants on the outer eggshell into the sterile embryo. The needle for punching the eggshell should not penetrate the embryonic cavity (the inner shell membrane, the chorioallantoic membrane or air cell membrane). While the penetration of the outer eggshell increased the relative pore volume about 30%, the risk for increased gas exchange of the embryo occurs.
Hygiene management including reduced air circulation, well maintained air filters, adjustment to weather conditions and well maintained hatchery insulation has to be taken into account when performing in ovo inoculation. Only strict management of these environmental factors can reduce the likelihood of infections of the egg, especially with aspergillosis or other air-borne pathogens. Continuous training of reliable staff is of the highest priority to prevent reduced hatchability and to maintain high hygienic standards. A sterile environment and the usage of chlorine based sanitizers are crucial. The storage and preparation of the vaccine in a separate biosecure area as well as strict precautions in using sterile devices such as containers and water should be implemented. While the cost of machine acquisition is high, the investment can pay back by its advantages.
The advantage of commencing immunity development before hatch can prevent young chicks from early infection after hatch. Since high tech machines are used for in ovo injection, the volume and concentration of the vaccine to be administered are highly standardised, reducing human error and labour cost when compared to vaccination of chickens later in life. Furthermore, vaccination of every single chicken can be ensured resulting in better uniformity of the flock. Coming with this is improved animal welfare due to less handling of birds later in life.
Currently, Marek’s disease, Newcastle disease, infectious laryngotracheitis and infectious bursal disease vaccines are routinely administered using in ovo vaccination in various countries. In ovo vaccination does not interfere with maternal antibodies that may still present in the embryo. In fact, it increases the level of immunity and as a consequence one injection is sufficient to offer life-long protection against the target disease.
This method involves the use of a hypodermic needle or similar equipment to introduce the vaccine into the muscle (usually the breast muscle) of the bird. The task is sped up greatly by the use of an automatic syringe which makes the technique relatively easy and doesn’t harm the bird. Care must be taken to ensure that the correct dose is administered to each chicken and the equipment should be checked regularly to ensure this.
Care must be taken to ensure that the needle does not pass through into a key organ and that other unwanted organisms are not administered to the bird at the same time by contaminated vaccine or equipment. Contamination can be prevented by good hygiene and vaccine handling procedures.
This method involves the use of similar equipment to that used for the intramuscular technique. The main difference between the two techniques is that, in this case, the vaccine is injected under the skin, usually at the back of the neck, and not into the muscle. Care must be taken to ensure that the vaccine is injected into the bird and not just into the feathers or fluff in the case of very young chickens. The dose being administered should be checked for accuracy frequently. Maintain good hygiene practices to limit introducing contaminating organisms during the procedure.
This method involves the vaccine being put into one of the bird’s eyes. From here the vaccine makes its way into the respiratory tract via the lacrimal duct. The vaccine is delivered through an eyedropper and care must be taken to ensure that the dropper delivers the recommended dose. If it is too little, the level of immunity may be inadequate, while if too much, the vaccine may not treat the total flock but will run out beforehand.
This method involves introducing the vaccine into the birds’ nostrils either as a dust or as a drop. Always ensure that the applicator delivers the correct dose for the vaccine being used.
With this method, the vaccine dose is given in the mouth. From here it may make its way to the respiratory system or it may continue in the digestive tract before entering the body.
With this method the vaccine is added to the drinking water and, as a consequence, is less time consuming and is significantly less stressful on the birds and operator. Take care to ensure the vaccine is administered correctly as there is much scope for error. The recommended technique observes the following:
This method involves the introduction of the vaccine to the mucus membranes of the cloaca with an abrasive applicator. The applicator is firstly inserted into the vaccine and then into the bird’s cloaca and turned or twisted vigorously to cause an abrasion in the organ. The vaccine enters the body through the abrasion. The technique is time consuming and stressful to the birds and care must be taken to ensure no contamination is introduced with the vaccine particularly from bird to bird. As a rule, the technique is not used on commercial farms.
With this method, the vaccine is introduced into the feather follicles (the holes in the skin from where the feathers grow). The technique involves the removal of a group of adjacent feathers or fluff in young chickens, and the brushing of the vaccine into the empty follicles with a short, stiff-bristled brush. Good hygiene is necessary to prevent the introduction of contaminant organisms with the vaccine.
With this method, the vaccine is introduced into the wing by a special needle(s). These needles have a groove along their length from just behind the point. When dipped into the vaccine some of the vaccine remains on the needle to fill the groove. The needle(s) are then pushed through the web just behind the leading edge of the wing and just out from its attachment to the body of the bird. Care must be taken to select a site free of muscle and bone to prevent undue injury to the bird. Ensure that the needles penetrate the layers of skin at the ideal site. A common problem is for the vaccine to be brushed from the needles by fluff or feathers before it is brushed into the follicles.
With this method, the vaccine is sprayed onto the chickens (or into the air above the chickens) using a suitable atomiser spray. The vaccine then falls onto the chickens and enters the body of other chickens as they pick at the shiny droplets of vaccine. A small quantity may be inhaled as well.
In the case of some vaccines, an important part of the procedure is to ascertain whether the vaccine has worked, or “taken”. A good example of this is fowl pox vaccine, which is administered by wing stab. Within 7 to 10 days after vaccination, a “take” should appear at the vaccination site. This is in the form of a small pimple one half to one centimetre in diameter. If the take is larger and has a cheesy core, it indicates that contaminants have been introduced either with the vaccine or with dirty vaccinating equipment. A check for takes would involve inspecting approximately 100 birds for every 10,000 vaccinated.
Another example of whether the birds are reacting satisfactorily to the vaccination is the systemic reaction found in chickens vaccinated against infectious bronchitis disease. In many cases, the birds react approximately 5 to 7 days after vaccination by showing signs of ill health such as slight cough, a higher temperature and lethargy. In cases where there are no obvious signs of success, blood samples may be taken and sent to the laboratory for examination. The usual test is for the presence of an adequate number of the appropriate antibodies (called the titre) in the blood. If the vaccination has been unsuccessful, it may be necessary to re-vaccinate to obtain the desired protection.
Failure to find evidence of success could be because of:
Faulty technique resulting in the vaccine not being introduced into the vaccination site.
Faulty vaccine – too old or not stored or mixed correctly. It would be unusual but not impossible for the vaccine to be faulty from manufacture.
The birds are already immune i.e. the immune system has already been triggered as a result of parental (passive) immunity, previous vaccination or other exposure to the causal organism.