Theses and Dissertations


Roy Mon Jacob

Issuing Body

Mississippi State University


Peebles, E. David

Committee Member

McDaniel, Christopher D.

Committee Member

Pharr, G. Todd

Committee Member

Evans, Jeff D.

Committee Member

Branton, Scott L.

Other Advisors or Committee Members

Leigh, Spencer A.

Date of Degree


Original embargo terms

MSU Only Indefinitely

Document Type

Dissertation - Campus Access Only


Agricultural Science

Degree Name

Doctor of Philosophy


College of Agriculture and Life Sciences


Department of Poultry Science


Mycoplasma gallisepticum (MG) is a major and economically significant pathogen of avian species. Different strains of MG have been used as vaccines in multiple-age commercial layer farms in an effort to protect the birds against more virulent field strains. The lower level of protection afforded by the low virulent MG strain vaccines provides an opportunity to the use of an overlay (revaccination) with an F-strain M. gallisepticum (FMG) later in their production cycles. In the present study, three trials were conducted to investigate the effects of prelay vaccinations of ts-11 strain MG, MG-Bacterin, or their combination, in conjunction with a FMG overlay after peak production in commercial layers. The following treatments were utilized at 10 wk of age (woa): 1) Control (no vaccinations); 2) ts-11 MG vaccine; 3) MG-Bacterin vaccine; and 4) ts-11 MG and MG-Bacterin combination. At 45 woa, all the birds in trial 1 and half of the birds in each treatment group in trials 2 and 3 were overlaid with an FMG vaccine. Various parameters including performance, internal egg and eggshell quality, blood, and visceral characteristics of the birds were evaluated. In this study, the ts-11 MG vaccination at 10 woa was shown to increase shell weight and the yolk lipid content of the eggs laid by the birds without affecting their performance. On the other hand, a prelay vaccination with MG-Bacterin did not prevent a drop in egg production in response to an overlay with FMG at 45 woa. A decrease in proportional infundibulum length in the control birds and MG-Bacterin vaccinated birds after being overlaid with FMG might be the underlying factor responsible for the observed decrease in egg production. Nevertheless, the prelay use of MG-Bacterin together with ts-11 MG didn’t appear to provide any additional benefit over the ts-11 MG vaccine alone on any of the parameters investigated. In conclusion, these results establish the potentially effective prelay use of the ts-11 MG vaccine in combination with an FMG overlay for the provision of continual protection against field strain MG infections, without eliciting any subsequent suppressive effects on the performance of commercial layers.