[Gumboro disease: assessment of the optimum time for vaccination by Deventer formula]
2007
The application of the Deventer formula (DF) was shown to be effective in choosing the optimum time of broiler chickens, replacement young meat and egg crosses against Gumboro disease (GD). The DF is based on calculation of the half-life period of antibodies measured in a neutralization test (NT): X=(A-B)xC+E+O-4, where X – a vaccination day; A mean arithmetic of the fowl presenting a percentage of the heard; B – working titer (ELISA), with which the vaccine works; C – half-life of antibodies in chickens from collected blood samples; E – the age of fowls when collecting samples; O-4 – additional expectation days prior to vaccination during blood sample collection in the period between hatching and day 4 of fowl life. NT is an old standard for detection of antibodies to GD virus and is from 3 to 3.5 days – for broiler chickens; 4.5 days - for young meat breeders and about 5.5 days – for egg crosses. The DF principle acts until there is a good correlation for half-life periods of antibodies according to ELISA-test and NT. The working titers were determined in the test system IDEXXstandard. Some examples were given to calculate the best vaccination age with vaccines Nobilis Gumboro 228E and Nobilis Gumboro D78 with working titers - 1:500 and 1:128, respectively. The advantages of DF were shown: the applicability for every fowl group, flexible schedules of blood collection for test; calculation for herds both with homogenous titers and heterogeneous titers of antibodies, application of all the types of vaccines against Gumboro disease. Poor sanitary conditions in birdhouses, careless administration of vaccine, high field pressure, that is, when field GD virus has higher infectious activity than the working titer of any vaccine used result in an error in calculation of vaccination date.
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