Chick Clinic ملتقى لكل مُهتم وعامل ومُشارك فى العملية الإنتاجية للطيور
REASONS FOR VACCINATION FAILURE
J.J de wit, T.H.F. fabri and j.f.
Heijmans Animal Health
Service, p.o.BOX9
7400 AA Deventer, The Netherlands
Protecting young chickens against infectious bursal disease virus IBDV, especially against the very virulent stains (VVIBDV) depends heavily on the use of vaccines. Vaccinating chickens may sound rather simple to do, but people with field experience know it is not. They all know about outbreaks of VVIBDV in vaccinated flocks. Causes of “vaccination failures” and possibilities to minimize the risk of “vaccination failures are discussed in this paper”
The possible causes of vaccination failures can be divided in three main groups: High field pressure, timing of the vaccination, and application of the vaccine
High field pressure 1-
When you administer a live IBD vaccine to chickens with still to many maternally derived antibodies (MDA), the vaccine will be neutralized by the antibodies. As a result the vaccine will not induce protection. This means that you have to wait with the vaccination strain is the breakthrough titer. More attenuated vaccines have lower breakthrough titers, and therefore have to be used at older ages compared to less attenuated vaccines. Intermediate plus strains can be used about two half life times (so about 6 days in broilers and 11 days in layer pullets) earlier than intermediate vaccines. Mild vaccines can be used again about 2 half life times later and are generally considered useless in countries with vvIBDV strains.
The vvIBDV stain has the highest breakthrough titer of all strains. This means that it can infect a chicken with MDA earlier than any vaccine. So, if a significant amount of vvIBDV virus is present in the house before vaccines can be used, outbreaks can be expected. Hygiene is the keyword in the attempt to prevent that a significant amount of vvIBDV enters the house or survives in the house (between cyclec). Rigorous cleaning (including using detergents) and disinfecting is essential to lower the level of infectious virus particles as much as possible. It must be lowered at least that much that before the amount gets significant again by multiplication in the next flock, a successful vaccination can be performed. As IBDV is a very resistant virus (it can survive for months in chicken houses), the disinfecting using 20 % formalin (temperature 20-25 C, relative humidity at least 70%) after thorough cleaning is recommended when the presence of IBDV field virus is suspected or known. It needs no explaining that the way a house is build, its condition (floor, walls, materials etc) have a major effect on the efficacy of cleaning and disinfecting. Also it must be considered that IBDV can survive for a long time in the environment. So a successful cleaning and disinfecting can be ruined in minutes when somebody or something enters the house without the proper hygiene procedures.
2- Timing of the vaccination
When a live IBD vaccine is administered to chickens with still to many maternally derived antibodies (MDA) for that vaccine, the vaccine will be neutralized by the antibodies. As result the vaccine will not induce protection.
It is impossible to see from the outside of the chicken how much MDA it got from the hens. In theory, the MDA will be much higher in chickens from hens that have been boostered with a oil based killed Gumboro vaccine than in chickens that originate from hens that were only vaccinated with a live vaccine. However in practice a wide variation in titres can be seen within and between flocks. Hens that have been vaccinated only with a live vaccine, can show high levels of antibodies, probably caused by a boostering during a subclinical infection during rearing or lay. The progeny of these hens has to be vaccinated later than normally expected. Also the mixing of progeny of different breeder flocks enhances the variability of titres within broiler flocks.
When the risk of getting a vvIBDV outbreak is low, the ago of IBDV vaccinations is usually based on general information. When the Gumboro virus is in the neighbourhood, one wants to vaccinate as soon as possible (but not to soon). In those cases, it is better to vaccinate for IBDV based on knowledge of the (broiler) flock itself. For these cases a help for estimating the optimal time of vaccination is developed: the vaccination date estimation. The principle behind estimating the optimal age of vaccinating is simple: measure the level of MDA at a very young age and, as there is a regular decline (log 2scale) of the MDA in a chick, it can be predicted when the level of MDA will be low enough to allow vaccination. There are different formulas available, from which the Deventer formula is explained in this paper (see further).
3- Mistakes in the application of the vaccine
3.1. Dosage
The use of less than one dosage of vaccine per chicken is a risk factor for vaccine failure, as it enhances the risk that a (larger) part of the flock will be unsuccessfully vaccinated. If it would be possible to use e.g. half a dose of vaccine without extra risk of vaccination failure, the vaccine producer would lower the amount of virus per dose himself. Putting less virus in a dose, would increase the profit margins for the producer considerably.
3.2. Water quality
As the vaccine is administered by water, the water quality can have a negative effect on the survival of the vaccine virus. Remains of disinfectants (e.g. cleaning the water system prior to vaccination), metals, high amounts of bacteria, or high temperature can shorten the half life time of the vaccine. When drinkers are used, they must be cleaned with hot water before the vaccination.
3.3 Addition of milk products
Addition of skimmed milk powder (2 grams per liter water) or sterilized defatted milk (1 liter per 50 liters of cold water) is recommended to stabilise the vaccine. An advantage of the addition of these milk products is the visibility (see3.4.4.) of vaccine containing water. The skimmed milk power is dissolved in lukewarm water. When the vaccine is going to be dissolved in this “milk” (e.g. when using dosage equipment), do it after the cooling down.
3.3. Vaccination procedure
3.3.1. Thirsting
To stimulate all chickens to drink enough of the vaccine containing water, the birds are thirsted for 2 hours (or longer depending on the length of the dark period of the lighting scheme).
3.3.2. Amount of water
Use of a low amount of water enhances the risk that part of the birds will not brink (enough) of the vaccine containing water.
When no lighting scheme is used: use 1.2 litres of cold drinking water per 1000 birds per day (of age). So vaccinating 20.000 birds at 14 days of age requires 20 × 1.2× 14 = 336 14 = 336 litres. When a lighting scheme is used: calculate based on the water amount of the previous day how much water was used in each lighting period. Divide the vaccine over 2 lighting periods. This means that the vaccination procedure is repeated twice that day, each time with half a dosage of vaccine.
3.3.3. Dead space
When the chickens have emptied the pipe, there still is a lot of water in the dead space of the pipes. This water must be removed from the pipes before the vaccination starts. At the end of the vaccination period, a part of the vaccine will be in the dead space of the pipes. Therefore, when the last of the vaccine water has been added in the drinking system, some fresh water is added to remove the vaccine water from the dead space (see 3.3.4.).
3.3.4. Water distribution
It is important that all chickens in the house have the same chance of being able to drink enough of the vaccine water. Chickens at the end of the same amount of water as the chickens at the beginning of the pipes. Therefore the vaccine water has already to be in the total length of the total length of the pipes before the chickens start drinking (start of the lighting period or after lowering of the pipes). This can be achieved by removing water (including that of the dead space) from the end of the pipe until milky (vaccine containing)
When a relatively low number of drinkers, nipples, cups or a pipe is used, the risk is enhanced that not all chickens can drink enough of the vaccine water.
CONCLUSION
It must be realized that the vaccination against IBDV will happen on an age that is a compromise between to soon (too many birds will neutralize the vaccine) and to late (enhanced period of unprotected birds). Each factor that adds an extra risk of having a less optimal vaccination enhances the chance that the compromise is getting off balance. Therefore, the vaccination must be performed with great care.
Also it is good to realize that it is more efficient to check for the quality of the vaccination in times of low field pressure (no or few clinical outbreaks), than starting to check it when there are complains a bout “vaccine failures”. Because then you are already to late.
