Theses and Dissertations

Issuing Body

Mississippi State University


Peebles, E. David

Committee Member

Lott, Berry D.

Committee Member

Downer, Donald N.

Committee Member

Morgan, Wallace

Committee Member

Willeford, Kenneth O.

Other Advisors or Committee Members

Gerard, Patrick D.; Ryan, Peter L.; Branton, Scott L.; Watson, Vance H.

Date of Degree


Document Type

Dissertation - Open Access


Animal Physiology

Degree Name

Doctor of Philosophy


College of Agriculture and Life Sciences


Department of Poultry Science


The F-strain of Mycoplasma gallisepticum (FMG) is commonly used in vaccination programs to displace infections by more virulent natural or wild type Mycoplasma gallisepticum strains. However, a better understanding of the mechanisms responsible for altered egg production (EP) and egg quality in commercial layers infected with FMG is important, as these alterations can cause economic loss to the United States layer industry. This study was designed to examine potential mechanism(s) responsible for alterations in EP and egg quality by FMG-inoculation. The effects of FMG on production parameters and physiological characteristics of commercial laying hens were evaluated. In isolation units, 12 wk FMG inoculation delayed onset of lay approximately one wk, decreased overall EP, and decreased EP 34 wk post-inoculation. A 12 wk FMG inoculation also resulted in a higher incidence of fatty liver hemorrhagic syndrome, ovarian follicular regression, and decreased isthmal and vaginal proportions of the reproductive tract. Ovarian regression may be related to retarded production (liver), transport (blood), and/or uptake (ovary) of yolk particles. Changes in blood characteristics (i.e. lipid composition) with FMG colonization of the liver may become manifest through changes in egg constituents. As evidenced through changes in the relative weights of various reproductive organs, colonization of these organs by FMG, in addition to the liver, may also be a cause of the effects observed on EP. Increases in hematocrit, serum triglycerides, and plasma protein between 8 and 10 wk post FMG-inoculation, suggest that the initial weeks of EP are stressful. Post-peak decreases in these same variables suggest a more chronic inhibition on lipid and protein synthesis in the liver. Decreased blood lipid concentration may be directly responsible for the reductions in yolk lipid, cholesterol, and fatty acid deposition in 12 wk FMG-inoculated hens. Dual adverse effects in the caged layer facility on feed conversion and egg mass were realized in 22 wk FMG-inoculated birds. In contrast, a 12 wk FMG inoculation delayed onset of lay without a loss in total EP or egg mass. Therefore, inoculation with FMG at 12 wk is more practical and cost effective. Higher degrees of physiological stress experienced by hens in a caged layer facility may exacerbate the effects of FMG inoculation seen in the isolation units. These data demonstrate that alterations in performance and egg characteristics of commercial layers inoculated with FMG at either 12 or 22 wk of age and housed in either isolation units or caged layer facilities are related to mutual functional disturbances in the blood, liver, ovary, and oviduct without concomitant intestinal changes.



lipid||hematology||blood||reproductive tract||small intestine||liver||layer||yolk||shell||Mycoplasma gallisepticum||egg||albumen