Vaccination - how much more can they take?
The merits of vaccination are plain to see – we see it in our pets and our own children, but as with the current MMR debate, the end user often questions the balance between possible risks and obvious benefits.
A natural response
Vaccination exploits the most natural of bodily reactions. When any animal meets an infection, the bodys defences (the immune system) reacts on two levels. Firstly, it mobilises cells and chemicals to kill the offending organism and prevent disease. Secondly, it triggers a memory system in the body to respond quickly should the animal meet that infection again some time in the future.
This can again be by primed cells to fight infection or the production of antibodies which are complex proteins circulating in the bloodstream. The antibodies will neutralise infections which have managed to reach the bloodstream. As an added bonus, these antibodies can be passed to the newly hatched chick via their yolk sac and protect the new chick for the first few weeks of life from the bugs the hen has been previously exposed to.
Specific protection
These protective measures are highly specific, ie they will only protect the bird against the specific organism they have been previously exposed to. Vaccination exploits this mechanism by priming the bird to the many diseases we expect they might meet later. Vaccines can be produced against a wide range of organisms and, for poultry, vaccines are available against viral, bacterial and parasitic diseases.
But just how much can the poor pullet take?
Much of our knowledge used to answer this question comes from the massive amount of work done by research workers and vaccine companies.
High quality vaccines
The first key is the production of high quality vaccines. All vaccines licenced for use in poultry in the UK have been approved by the authorities, the Veterinary Medicines Directorate (VMD), and have to satisfy three broad categories on quality (the vaccine in the bottle is what is says on the label), safety (the vaccine will not harm the environment, the user, you, other in-contact birds) and efficacy (it does what is says on the label, ie it works!).
Part of this process of licencing is designed to prove that the vaccine works in practice and is compatible with other vaccines given. This is very relevant for multi-component vaccines with the requirement to show that the bird can react efficiently to all the individual components. Specific details on all these aspects are given in the product literature and datasheets.
Technique
The next aspect, once you accept you have a good quality vaccine, is to administer it to the birds in the most effective way such that the birds respond in the most efficient manner. This has been covered in a number of previous articles. Broadly speaking, vaccines can be given by injection, via the drinking water or by spray. Injection is the usual route for killed vaccines as these won't spread from bird to bird and you need to be certain every bird gets its own dose. Examples are the triple Newcastle/EDS/IB vaccine, Salmonella or Pasteurella.
These vaccines can be given under the skin (subcutaneously) or into the leg or breast muscle (intramuscularly). Here you only get once chance so it is imperative that vaccination gangs are well trained and highly skilled. As this involves sticking a needle into the bird, it is also imperative that the highest standards of hygiene and cleanliness are observed.
Live vaccines are easy to use for mass administration to large flocks as they can be given via the drinking water or spray, or even by individual eye drop. Common examples are IB, ND, TRT, ILT and Epidemic Tremor, often to act as primers for later killed vaccines.
Spraying vaccines
Spraying live vaccines is especially good for protecting against bugs which attack the respiratory tract as you are putting the vaccine where it needs to produce its best protective effect, ie the lining of the nose and windpipe.
The key here is to supply the right droplet size to as many birds as possible. This requires good spraying technique and good equipment. Vaccine companies offer excellent assistance in on farm auditing of your vaccination technique and this can be arranged via your veterinary surgeon.
Drinking water vaccination
Drinking water administration is potentially the easiest option, requiring little in the way of expensive equipment and enabling a large number of birds to be vaccinated in a short space of time. However, familiarity breeds contempt and ease of administration should not be an excuse to take it for granted. There must be a sufficient number of well cleaned, well maintained drinkers, a clean system for delivering this, including the header tank, and knowledge of the drinking behaviour of your birds. It requires ample time for preparation of the drinkers and the vaccines. Again there is much useful technical advice on hand from your veterinary surgeon and the vaccine companies.
How does the bird respond?
Returning to the question originally posed, it has been shown by experiment, research and practical experience, that pullets are able to respond well to a wide range of vaccines as long as they are good quality and applied appropriately. After all, this is the most natural of responses to all sorts of challenges as occurs to birds in the wild as well as birds in commercial production.
To date, there has been no evidence that we have reached any sort of overloading of the system in the range of vaccines we administer to our birds.
Good nutrition is essential
As indicated earlier, the antibodies we hope the birds will produce in response to vaccination are proteins. To produce these, the birds need to be in good health at the time of vaccination and on a high plane of nutrition to provide the building blocks for these proteins.
Conclusions...
The modern pullet is at risk from an increasing number of infectious challenges. Some can be life threatening or capable of causing significant disease in affected birds (eg coccidiosis, Pasteurella, Newcastle disease, IB and Mycoplasma). Others can have an adverse effect on egg production or quality (eg IB, IB variants, EDS, TRT) whilst still others may have public health significance (eg Salmonella).
Vaccination programmes need a lot of careful planning to ensure that birds can respond in a most efficient way during their rearing. This can be 'topped up' by the strategic use of selective live vaccines through lay.
We expect, and are dependent on vaccine companies to supply us with up to date, efficient and cost effective vaccines. In return, it is up to producers to administer these vaccines to the birds in the most effective manner, through careful planning – birds which are in the best possible health and able to respond in the way we would expect.