Submitted to: Avian Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/10/2011
Publication Date: 9/15/2011
Citation: Purswell, J.L., Evans, J.D., Branton, S.L. 2011. Serologic response of roosters to gradient dosage levels of a commercially available live F strain-derived Mycoplasma gallisepticum vaccine over time. Avian Diseases. 55(3):490-494. Interpretive Summary: Spray application of Mycoplasma gallisepticum (MG) vaccine is a time and labor saving means of vaccine administration for layer chickens. Efforts to characterize the spray vaccination process have illustrated that spray characteristics, carrier media temperature, and carrier media ionicity can affect the success of a spray vaccination program. Inhalation, topical deposition on the eye surface, and secondary contact are considered the most likely routes of vaccine uptake under spray application, and as such lower vaccine load is presented to the bird when compared to traditional eye-drop administration. However, the minimum effective dose for live F-strain MG vaccine is unknown, nor is the progression of seroconversion over time. Estimates of minimum effective dosage were obtained from administration of gradient dilutions of commercially available live F-strain MG vaccine. Minimum dosage required to elicit seroconversion was observed at 10-3X at six weeks post-vaccination. Higher doses were correlated with earlier seroconversion. The dose required to reach 90% seroconversion at six weeks was estimated to be 0.26 X.
Technical Abstract: Spray application is a commonly used time- and labor-efficient means to deliver live Mycoplasma gallisepticum (MG) vaccine to laying hens in commercial production facilities. The dosage of vaccine received by spray vaccinated birds can vary due to variation in the spray plume and vaccine suspension droplet trajectory. In this study, a total of 48 Hy-Line W-36 males were placed individually in isolation units following eye-drop application of gradient levels (1X, 10-1X, 10-2X, 10-3X, 10-4X, 10-5X, 10-6X, and unvaccinated control) of the MG vaccine. The determined titer associated with a 1X dose was 2 × 106 cfu/dose. Serological response was assessed weekly following vaccination via serum plate agglutination (SPA) for weeks one through seven post-vaccination (p.v.). In addition, immunological response was assessed at wks five, six and seven p.v. via MG ELISA. As indicated by SPA analyses, a 1X dose of vaccine resulted in 100% seroconversion and dose levels of 10-1X and 10-2X resulted in 75% and 37.5% seroconversion, respectively at six wks p.v. MG ELISA results at six wks p.v. demonstrated immunological responses in100%, 57.1%, and 28.6% of the 1X, 10-1X and 10-2X dosed birds, respectively at six wks p.v. The lower dosage levels of 10-3X, 10-4X, 10-5X, and 10-6X did not elicit a response from any bird at six wks p.v. Utilizing the SPA data, a logistic regression model was used to determine the relationship between dosage level and seroconversion rate (R2 = 0.999 with a standard error of prediction of 1.6%). The model predicted a required effective dosage of 0.26X for 90% seroconversion at 6 wks p.v. under test conditions.