Today’s large poultry operations prefer to use mass application techniques for vaccination with live vaccines.
Even though these techniques involve application to thousands of birds at one time, the aim is the same as for individual bird vaccination: deliver a minimum of one dose of vaccine to the immune system of each bird. Not only does the dose of vaccine have to be adequate, but it must be alive when it reaches the birds in order to replicate and cause an immune response. Our aim is to vaccinate the highest possible proportion of birds in a flock. This prevents the proliferation of a field pathogen on a farm and thus minimises the effects of a particular disease.

The actual proportion of birds which need to be effectively vaccinated will vary according to the infectious agent involved, the current disease situation and the type of vaccine. Mass application through the water offers the advantages of lower labour costs, minimal bird stress and stimulation of good mucosal immunity.

Its main disadvantages are inconsistencies of vaccine dosage depending on water consumption, and the potential for some birds to receive no vaccine at all. Incomplete coverage of the flocks can result in post vaccinal reaction and/or ‘heating up’ of vaccine virus due to repeated bird to bird transmission. Although vaccination via drinking water would seem to be the least labour intensive it is certainly not the simplest and fastest method if we want to do it correctly.

All live virus vaccines must reproduce themselves within the host before they can stimulate a protective immunity. They do this primarily by attaching themselves to target cells within the host and then causing the cells to make identical virus particles.

This is the phase that results in the vaccination reaction or ’take’, which accompanies the use of live virus vaccines. The replication of the vaccine virus prompts the host to produce circulating and local protective antibodies against the particular virus. It follows therefore that three things are critical in this sequence of events:

1) The virus must still be alive when it reaches the host.
2) Sufficient live virus particles must reach target cells to stimulate a protective response on the part of the host.
3) Each member of the flock must receive sufficient live virus particles since further spread of virus within the flock     cannot generally be relied upon to stimulate uniform protection.

Live vaccine viruses are quite stable so long as they are in freeze dried form and stored in the fridge. Once they are in diluent they begin to die after a while. Normally the farm’s water is the diluent for the vaccine.How suitable a diluent this is depends on several factors. It follows that everything possible must be done to keep as much of the virus contained in the vaccine alive and to ensure that all birds have a chance to receive enough vaccine. Live virus vaccines are particularly susceptible to

1) Ultraviolet light: No exposure to sunlight,
2) Heat: No prolonged exposure to high temperatures. The drinking water should be cool i.e. 15-20 ̊C,
3) Heavy metals: don’t use utensils or drinking water containing these. Use plastic buckets or containers for     vaccine reconstitution. Check the water quality and use only trusted suppliers if any,
4) Chlorine: Do not administer vaccines in drinking water containing chlorine,
5) Disinfectants and detergents: make sure that all utensils are free from traces of these,
6) Organic matter (litter,feed etc): make sure that all tools and drinkers are clean to use,
7) Moisture: Do not use the contents of damaged vials. Also don’t break the seals on the vaccine vials until you     are ready to reconstitute the vaccine.

The major concerns in water vaccination are those of prevention of inactivation and proper distribution of the live vaccine. Inactivation of the vaccine virus can be prevented by 1. Rapid administration and by 2. Protection of the virus particles from inactivating agents which may be present in the water and water lines. You should also consider the safety of water lines for a possible deactivation agent for vaccine virus.

Emphasis is always placed on proper handling, storing and mixing of the vaccine but all these efforts can be quickly spoiled by an improperly maintained water system. Sanitising products in the water such as chlorine, ammonia compounds or acidifiers like citric acid; residual sediment in the water lines and in the filters will inactivate the vaccine virus. The sediment in the water system can bind with or destroy vaccine viruses. Failure to protect the vaccine may lead to partial protection only against the disease.

It is advisable to check the quality of the drinking water on a regular basis. Too high or too low pH can have a negative effect on the efficacy of the vaccine virus. In addition a chlorine level as low as one ppm or contamination with heavy metals for example may inactivate the vaccine virus.

As well as problems surrounding the quality of the drinking water there are various problems connected with the extensive range of drinking water installations available. For example there are some systems which are difficult to drain and retain substantial volumes of chlorinated water in their ‘dead spaces’. If drinker lines are not drained before vaccination the residual water in them cannot only neutralise vaccine virus but slow down its distribution as well. In such a case, birds at the top of the shed may consume enough vaccinated water whilst the ones at the bottom of the shed may receive no vaccine at all.

It is therefore essential to allow birds to drink only after the drinker lines have been drained and then primed with vaccinated water.

One of the difficulties associated with vaccination of caged pullet flocks is over-consumption of the vaccine solution by birds at the inlet end of the water line. Birds further down the water line may not receive vaccine solution, which results in uneven vaccination of the flock. This can be a particularly acute problem when the flock is excessively thirsty at the time of vaccination or when the vaccine volume is insufficient. It was observed using a dye in a caged pullet house that the vaccine solution did not even reach the end of the cage battery by the time all the vaccinated water had disappeared from the header tank. A remedy to this problem might be to close the water system for the night, let the birds drink out all the water from the lines and prime the lines with vaccinated water solution before lights come up in the morning.

This way all the birds have equal chance to take the vaccine as long as the header tank contains enough water for the duration of vaccination. Depending upon the water system design, water lines of different cage batteries may not fill at the same time. The result of this unequal filling rate is that exposure time to vaccine solution is not equal throughout the house, leading again to uneven vaccination.

Each house needs to be evaluated individually to determine the best approach towards vaccination.

Bluefarm has the ability to mark birds having consumed vaccine solution by temporarily staining their tongues. It has been observed that the intensity of tongue staining varies depending on the amount of vaccine solution consumed. The intensity of tongue staining is related to the protection offered by vaccination.

Newcastle Disease challenge of vaccinated birds having different degrees of tongue staining has demonstrated that birds with more intensely stained tongues were better protected than those with lightly stained tongues. Bluefarm also can be used in trialvaccinations to evaluate vaccination technique or to check the water system. If you want to monitor whether vaccinated solution has reached all the drinkers 1 sachet (15 g) to 100 litres of water is sufficient. To have a reasonably accurate picture about success or failure of vaccination, pick up 50 birds from each corner of the shed and look at their tongue and crop. If vaccination has been done correctly, at least 90% of the tongues and crops should be coloured blue.

Dont forget : The success or failure of vaccination depends on the administration of vaccines. You must keep in mind however, that you cannot achieve 100% protection by vaccination only. Massive numbers of infectious agents are sometimes capable of breaking through the immunity of a flock like floods break through dams. This is why it is so important to implement bio-security and hygiene measures to minimise entry and spread of pathogens to and within a farm so reducing infection pressure.