Stochastic Estimation of Optimal Age for Infectious Bursal Disease Vaccination in Broilers in Paraguay

Abstract

In Paraguay, vaccination programmes for infectious bursal disease (IBD) virus control planned by foreign vaccine manufacturers are commonly used, which are not always adapted to the particular conditions on the farm and to the status of maternally derived antibody (MDA) in chicks. The objectives of this study were to fit a generalised linear mixed model for MDA titre values for estimating optimal days of age for IBD vaccination in broiler flocks, and to assess how optimal vaccination timing estimates differ between flocks. The MDA titre values were measured by enzyme-linked immunosorbent assay (ELISA) with sera collected from 20 chicks per flock (n=14) at 1, 8, 15 and 30 days of age. Markov chain-Monte Carlo method was used to fit a generalised linear mixed model for the dependent variable “log-transformed MDA” at 1, 8 and 15 days of age. Optimal days of age for IBD vaccination for the reference flock, and differences in optimal days of age between flocks were estimated. The study chicks were vaccinated according to the estimated optimal days of age. Data collected at 30 days of age were only used for checking a rise in antibody titres after vaccination. The mean log-transformed MDA titre values at hatch was estimated 12.35 [95% Bayesian credible interval (BCI) : 12.16-12.53] and half-life period of log-transformed MDA titre values was 3.7 days (95%BCI : 3.5-3.9). Given the use of intermediate vaccine with breakthrough titre value of 125, the optimal vaccination timing for the study flocks is at least seven days later than the recommended timing by the vaccine manufacturers. The results can be used as a standard to create IBD vaccination programmes, however it is recommended for estimating the vaccination timing to measure the MDA status on a routine basis.