By P W Cargill, Merial Avian Business Unit UK and Joey Johnston, Merial Avian Business Unit, USA. 

Planning and attention to detail resulting in better administration will improve disease control and therefore economic performance of poultry. The following is an overview of the principles of poultry vaccination.

Mass Vaccination Techniques

Flock sizes of commercial poultry operations can be as high as 45,000 birds in a single air space. For this reason it has become necessary to evolve effective methods of mass vaccination. The aim is to vaccinate a high enough proportion of the birds in the flock, to prevent or minimize the effect of a particular disease.

The proportion of the birds that need to be effectively vaccinated will vary according to the infectious agent involved and the current epidemiological situation with respect to that agent.
In many situations, vaccination may only be employed as a means of minimizing the economic impact of a disease rather than total prevention in 100% of the flock.

Commercially produced vaccines are available in presentations tailored to large flock sizes. While the principles of administration remain the same, the techniques used for the mass application of vaccines need to be adapted to small flocks of birds.

Vaccine Types Available

There are two main types of vaccines available for poultry:

1. Live attenuated vaccines

Again, due to flock size, the most widely used vaccines are live attenuated virus vaccines which can be administered to birds by techniques which are practical within the limitations of the production environment. This is usually by means of the drinking water or by spray application, though some live vaccines require individual application by eye drop or administration by injection.

2. Inactivated vaccines

Inactivated vaccines are usually employed in breeding or laying stock and require individual administration by injection. All contain some type of adjuvant in order to optimize the immune response to the antigen. Commonly used adjuvants include mineral oils and aluminium hydroxide.

Administration Techniques

• - Drinking water
• Spray/nebulisation - at day of age. Birds in the housed environment
• Eye drop
• Transfixion and scarification (cutaneous route in the wing web or foot)
• Injection - intramuscular or subcutaneous
• In-ovo administration

Drinking Water Administration

Drinking water administration is an appropriate method of administration for most live vaccines, particularly for diseases such as infectious bursal disease and avian encephalomyelitis where the target organ is the gut. The presence of a choanal cleft in poultry also allows this route to be employed for most respiratory virus vaccines, vaccine virus gaining entry to the nasal cavity from the mouth via the cleft.

Live vaccines by their nature have a limited lifespan that must be taken into account during administration. As a rough guide 1.5 to 2.0 hours is a typical period of time over which live vaccines should be administered. The aim should be to present the vaccine in the water to all the birds in the colony over this 1.5 to 2.0 hour period.

One of the limitations of this method is that we must be sure that all the birds in the flock will drink over the period of time over which the vaccine is presented to them. Various means are available to encourage this situation such as controlled lighting, controlled feeding or water deprivation.

Feed and water intake are closely linked in poultry, therefore presenting food will stimulate water consumption. Water deprivation can also be useful, however this must be used with caution as excessive deprivation can stress the birds to a level, which can predispose disease and adversely influence vaccine efficacy and feed efficiency. Controlled lighting will affect water consumption by influencing activity and feeding patterns.

Live vaccines are as susceptible to antiviral agents as field viruses, and it is important to ensure that the vaccine does not come into contact with disinfectant, chlorinated water or water sanitizing materials commonly used on farms.

Basic steps can be taken to minimize the risk of exposure of the vaccine to these chemicals. These include washing hands thoroughly (rinsing soap off thoroughly), only mixing vaccine in a clean area on a clean surface and ensuring that vaccine vials are not placed on surfaces that may carry traces of disinfectants and consequently contaminate the water during mixing.

The volume of the water necessary for the vaccination period should be calculated and the influx of mains water into the tank interrupted until the completion of vaccination. Chlorinated water is hazardous to vaccines and can severely reduce the amount of vaccine virus presented to the birds.

The addition of skimmed milk powder to all water, which will come into contact with vaccine, is a simple and effective way to overcome the detrimental effects of the chlorine. The milk powder must be mixed at the correct rate of 2-2.5g/litre or 10g/gallon and the powder should be mixed with the water at least 20 minutes prior to the vaccine being added.

With a clean plastic bucket, some of the milk treated water should be removed from the tank. Remove the metal caps from the vaccine vials and submerge each bottle in the water before removing the rubber stopper, rinsing the entire contents of each vaccine bottle. Once the vaccine has been added to the water reservoir of the delivery device, the water should be mixed thoroughly ensuring even distribution of the vaccine.

It is very important to prime the drinker system, as the pipework will contain water with no vaccine. Due to their design, nipple drinker lines will contain large amounts of water even if they have been drunk dry by the birds. An additional advantage of using milk powder is that it acts as a useful visual marker for the vaccine and the drinker lines should be drained until the milk is visible. Approved dyes may be added as an indicator.

Once vaccine is presented to the birds, stimulating activity by increasing light intensity, operating feeders and walking through the birds are all effective at encouraging drinking.

Bell drinker systems present more difficulties in terms of priming the drinkers with vaccinated water. The only practical solution to eliminate unvaccinated water is to walk through the shed, tipping each drinker until they fill with water containing milk powder.

An alternative approach is to deliver a measured dose, manually to each drinker in the shed, however the water supply must be treated with milk powder and it is important to ensure adequate mixing of the vaccine in each drinker.

Due to the diversity of drinker system design and plumbing routes in houses, it is important to tailor the method of vaccination to the particular equipment in use. Mock vaccination using special dyes capable of temporarily staining the bird’s mouth are a useful means of proofing vaccination technique.

Spray Administration

Administration of respiratory virus vaccine by spray is another very effective method of vaccination. Spray administration is employed in two situations that are distinctive for both
practical and technical reasons. These are:

• Spray administration to day old birds in delivery boxes
• Spray administration to birds in poultry houses

Spray Administration at One Day of Age

The day old birds contained in delivery boxes represents the situation where we have most control of the birds in terms of our ability to administer vaccines. Birds are in groups of 80-150 and their close proximity facilitates physical lateral transfer of vaccine.

The physical size of birds does not facilitate the delivery of vaccine directly to the respiratory system, as no currently available equipment is capable of producing a consistent particle size capable of inhalation.

The aim should be to apply vaccine onto the birds, some of which will enter the eye but most will be taken in orally. Day old birds will readily take very small drops of water off each other and the flat surfaces of the box.

The spray employed should be capable of distributing the vaccine evenly over the birds. The volume applied must be accurately determined and repeatable for every box and can range from 7ml to 40ml per 100 birds depending upon the vaccine and particular spray equipment in use.

For practical reasons droplets of 100-300µ diameter are ideal as they facilitate even coverage of birds. Smaller droplets have a tendency to drift with air movement and may not reach the box. Due to the small volumes of water used during spray administration, all water used for vaccine reconstitution should be fresh, cool distilled water as water temperature also has an impact on vaccine life.

Excessively hot water will seriously reduce the titre of the vaccine. The possible effect of the water chilling the birds must be taken into consideration when deciding on volumes to be employed. From a practical point of view a spray pattern that easily facilitates coverage of all the birds in the box is ideal.

Equipment designed to administer vaccine by means of a ‘flat fan’ nozzle onto a box on a moving conveyor are usually more effective in terms of the extent of coverage of the chicks achieved. The nozzle should remain vertical above the box during the procedure and care taken that the entire inside area of the box is covered.

Some types of spray equipment will measure a pre-determined volume each time it is operated, others must be calibrated on the basis of the volume delivered in a unit time and the dose applied to each box determined by the time that the spray is applied to each box.

Pressurized spray equipment must have the operating pressure maintained and time which the spray is applied should be measured and not guessed if effective application of the vaccine is to be achieved. Compressed air quality must be monitored in order to ensure freedom from bacterial and oil contamination generated in the compressor.

Spray Administration to Housed Birds

The rapid growth rate of modern poultry breeds means that at the age where respiratory virus vaccines are required the physical size of the birds is considerably greater than at day old. For this reason it now becomes possible to administer vaccine directly to the respiratory system if so desired. In practice, vaccine is usually administered by two main means of producing a spray.

The pressurised spray apparatus

This consists of a pressure chamber, lance and nozzle. The nozzle and the operating pressure vary the size of the particle produced, but this type of equipment will produce a large range of particle sizes from 50-1000µ in diameter. One of the practical difficulties with this method is that spray particles produced this way will only travel approximately 50cm from the nozzle.

Therefore in order to vaccinate all the birds the nozzle must come within 50cm of every bird in the group. Due to the range of particles produced only a small proportion of vaccine is capable of being inhaled by birds, the remainder is either taken up by the ocular oral route or falls on the ground. A consequence of this is the need to employ relatively large volumes of water to cover the birds, which can be in the order of 15-30 litres per shed of birds.

Controlled droplet application devices

Spray technology developed for horticultural and insect control use is directly applicable to poultry vaccination. These devices are capable of producing a narrow band of particle sizes in a predetermined range.

The spray is generated by centrifugal force and water is delivered to a spinning disc on the circumference of which the spray is formed. The nebulized vaccine can then be blown by means of a fan, in order to facilitate delivery to the birds. One of the advantages of this type of equipment is that they are able to produce a particle size between 80µ and 100µ resulting in inhalation of the particles and their deposition in the upper respiratory tract.

This type of equipment also delivers vaccine in a band approximately 1m in width and 3m in front of the machine that enables the operator to easily administer vaccine to all the birds. The volumes of water required are also relatively small, because only particles in the desired range are produced by the machine, this means up to 30,000 birds can be vaccinated with as little as 900ml of water. Again, as water volumes employed are relatively small, all vaccines should be reconstituted in cool, fresh, distilled water.

It is advisable to contact the relevant manufacturer for information regarding the most appropriate spray equipment for each vaccine. Again, from a practical point of view it is important to ensure that all the birds are administered with the spray at the same time. Shutting down the ventilation system will minimize air movement in the shed and prevent 'drift' of vaccine.

Reducing the light level until bird movement is minimized is also essential. Once these two measures are taken the spray should be applied to the birds as evenly as possible by following a logical and systematic route through the birds whilst spraying. It is often useful to approach the process by aiming to apply the spray to the entire floor area of the shed, the birds being incidental to the process and the route being determined by the technical attributes of the equipment being employed.

Eye Drop Administration

Eye drop administration is probably the most effective (but labor intensive) means of administering live respiratory virus vaccines to birds. Each bird is individually handled and receives a full dose of vaccine. The process facilitates both local and humoral immunity due to the presence of the Harderian gland behind the third eyelid. Eye drop diluent is available from vaccine manufacturers for use with certain vaccines and is presented in an easy to use bottle, which usually contains a dye in order to assess the efficiency of administration. Birds dosed effectively will show staining at the nares shortly after vaccination.

Care must be taken over the process to ensure that the fluid does not 'roll off' the eye due to the surface tension of the droplets. Each bird should be held until it blinks after the droplet is applied and the whole process must not be rushed or birds will be missed.

Transfixation and Scarification (Cutaneous Route)

This method delivers the vaccine into the skin thickness and is the method used exclusively for fowl pox vaccination, though avian encephalomyelitis is often combined with the fowl pox vaccine. The site most widely used for application is usually the skin of the wing web (using a special two pronged, grooved applicator) though scarification of the skin of the thigh and the foot can also be used. It is very important to ensure that fowl pox vaccine does not come into contact with the eyes or mouth of the birds. This can lead to lesions appearing in these organs.

In practice the most common complication can occur if the vaccine is applied to the skin under the wing where birds occasionally place their head when sleeping. Birds can subsequently develop lesions on the head that may be severe enough to affect the mouth and eyes with subsequent adverse effects on food and water consumption.

Care must also be taken to remove all used vaccine vials and scarifying equipment from the shed after vaccination as birds will peck at these items which can also lead to oral lesions.

Injection

Intramuscular or subcutaneous injection is the most common route of administration employed for oil and aluminium hydroxide adjuvanted vaccines and some live vaccines. Vaccine is usually available in 500 or 1000 dose bottles, which feed an automatic syringe at a preset dosage that facilitates vaccination of large numbers of birds.

The site of administration is most commonly into the breast or leg though the lower neck can also be used. Accuracy of placement of the needle is critical as incorrect placement can lead to granuloma formation, lameness, head swelling or liver puncture depending on the injection site. The method and care of handling birds during this procedure is also important as this can contribute to lameness in birds.

A 12.5mm (1/2"), 19 gauge needle is suitable for use and should be changed at least every 200 birds in order to avoid spread of bacteria and viral contaminants. Attachments for automatic syringes are now available which decontaminate needles between each bird and are a useful aid in minimising the risk of cross contamination. A needleless injector system is also available for use with some vaccines, which significantly decreases the possibility of hygiene complications associated with needles as well as improving the consistency of the vaccine delivery into the bird.

In-ovo Administration

This is a process by which vaccine is administered into fertile eggs via the air cell at between 17.5 and 19 days of incubation using a special machine.

The system has proved to be effective for the administration of Marek's disease vaccine, certain types of infectious bursal disease vaccine and may be appropriate for a number of other types of live vaccine. This is a rapidly growing area of vaccine technology which will generate a number of other vaccines developed specifically for in-ovo administration.

December 2006