Abstract
Newcastle disease outbreaks still occur sporadically in commercial vaccinated flocks and remains a constant threat to poultry producers despite advances in vaccination against the disease. Another aspect that can be a complementary control strategies or that is well recognized but is often neglected is the differences in immune response due to genetic or breed/type variation. This study investigated the immune responses to LaSota vaccination in light weight type or breeds of chickens (pullets) and heavy weight type or breeds of chickens (broilers) used in commercial poultry production. Fifty seven-week-old White Marshall broilers (Br) and 50 Isa Brown pullets (Pu) of the same age were randomly divided into 4 groups viz: vaccinated broilers chickens (VaBr), unvaccinated broiler chickens (UBr), vaccinated pullet chickens (VaPu) and unvaccinated pullet chickens (UPu). Chickens in groups VaBr and VaPu were vaccinated with LaSota vaccine while groups UBr and UPu were not vaccinated. The chickens were observed for clinical signs and lesions. Serum samples were collected from the chickens in all the groups on days 0, 7, 14, 21, 28 post vaccination (PV), and assayed for haemagglutination inhibition (HI) antibodies. The geometrical mean antibody titres (GMT) of the pullets were 2 to 3 times higher than those of the broilers on days 7 to 28 PV. Vaccination produced neither clinical signs nor lesions. The above observations show that naturally pullets produce higher antibodies than broilers, and suggest breed-based variation on immune responses to Newcastle disease vaccination. The knowledge from the present study may lead to genetic approach to vaccine development and development of more effective vaccination strategies to be used in commercial poultry production.
Key words: Broilers, Haemagglutination inhibition antibody, LaSota vaccination, Pullets
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