Submitted to: Avian Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/1/2007
Publication Date: 12/10/2007
Citation: Evans, J.D., Leigh, S.A., Branton, S.L., Collier, S.D. 2007. Effects of increased dosages of the Mycoplasma gallisepticum vaccine MYCOVAC-L® in layer chickens subsequently challenged with virulent M. gallisepticum: egg production and serologic response. Avian Diseases 51:912-917. Interpretive Summary: Mycoplasma gallisepticum (MG) is the most economically significant mycoplasma specie impacting both meat- and egg-type poultry and is frequently encountered within poultry industries worldwide. MG infections can yield economic losses in the form of reduced feed efficiency and egg production and/or increased mortality and carcass down-grades. MG control strategies commonly used within the poultry industry include intense biosecurity and biosurveillance within the turkey and meat-type sectors. In addition, live attenuated MG vaccines have been approved and are widely used within the layer industry. Towards effecting more efficacious means of control, studies have been initiated to optimize the vaccine-associated protocols. Variables currently being considered include practices/techniques of vaccine reconstitution and application. Effective dose- or titer-determination may also enhance vaccine effectivity by optimizing antigen presentation to the host’s immune system and/or by enhancing in vivo persistence of the live vaccine. In the current study, layer chickens were treated with the manufacturer’s recommended dosage of a live MG vaccine, MYCOVAC-L® or at fifteen-fold (15X) that level. Vaccinated birds were subsequently challenged with a virulent strain of MG. Study-associated findings showed that the birds were not adversely effected by the higher dosage (15X) of the vaccine and that these birds were better protected from the virulent MG challenge, as evidenced by the lack of egg production losses. While the current study does not necessitate the use of such an extreme dosage for this live MG vaccine, it does indicate that further work is required to determine the minimal dosage rate necessary to effect maximal protection.
Technical Abstract: Ten wk old Hy-Line Commercial W-36 pullets were spray vaccinated with MYCOVAC-L® at the manufacturer’s recommended dosage (1X) or at fifteen-times (15X) that rate. At 22 or 45 wks of age, subsets of 1X and 15X vaccinated pullets were challenged via intraocular inoculation with the virulent Mycoplasma gallisepticum (MG) strain Rlow. The birds were maintained in biological isolation units through 55 wk age. Percent hen-day egg production was determined through wk 55 and individual egg size was determined for eggs during wk 27 and 50 (or 5 wks post-virulent MG challenges) for all treatment groups. Analyses for treatment effects on overall (22-56 wk) percent hen-day egg production revealed no significant differences for non-challenged 1X and 15X treatments. Among 1X vaccinated groups, Rlow challenge at 45 wk corresponded with significantly (P'0.01) lower overall egg production as compared to the unchallenged 1X-vaccinated control (70.88 vs. 79.15%, respectively). Conversely, at the 15X dosage level, overall egg production was not significantly impacted by virulent MG challenge at 45 wk when compared with its unchallenged counterpart (84.09 vs. 81.03%, respectively) and may indicate increased protection from virulent MG challenge. Egg size (weight) of treatment-associated eggs was not affected by treatment as measured at 27 wk, but similar comparisons at wk 50 did identify small but significant treatment associated differences.