Serological patterns in broilers in the U.K.

Broiler chickens are vaccinated much less intensively than parents.

The objectives of vaccination are :

1. To protect the broilers against mortality and morbidity/reduced productivity during rear.

2. To control the level of condemnations at slaughter

3. To reduce or eliminate the transmission of pathogens to successive crops on the same farm or to other farms.

Serological monitoring of the response to vaccination is practiced much less intensively than in the parents. Since most of the vaccines used are live they may be inducing a local or cell-mediated immune response even if there is not a detectable humoral antibody response. The great majority of broiler samples tested during the period 1993/1994 were collected at slaughter (usually at 38-44 days, some as old as 56 days). The most common reason for submission of these samples was excessively high carcase condemnation rates. No data have been excluded except for records for which the age of the birds was not informed or recorded.

Table 6 below summarizes the results of a series of over 53,000 tests. For Elisa assays the kit manufacturer is identified in brackets (Sv = Svanova, Gui = Guildhay, CVS = Cambridge Veterinary Sciences, Idx=Idexx).

In the case of the IB 793B variant tests a high proportion of samples are positive, however the Central Veterinary Laboratory has indicated that titres below Log2 6 (1:64) may be due to cross-reaction arising from infection with other serotypes.

All sera tested for M.g. and M.s. (serum-agglutination) were negative. The pattern of response for the other assays is presented in a series of figures on the following pages.

Detailed information on Specific Diseases: