Effects of 6/85-strain Mycoplasma gallisepticum vaccination alone at ten weeks of age or in conjunction with F-strain Mycoplasma gallisepticum inoculation overlays at twenty-two or forty-five weeks of age on the reproductive and digestive organs of commercial egg-laying hens.

Two trials were conducted to determine the effects of a prelay 6/85-strain Mycoplasma gallisepticum (6/85MG) vaccination alone or in conjunction with time-specific F-strain M. gallisepticum (FMG) inoculation overlays on the gross reproductive and digestive organ characteristics of commercial egg-laying hens. In each trial, the following 4 treatments were applied: 1) sham vaccination at 10 wk of age; 2) vaccination of 6/85MG at 10 wk; 3) 6/85MG at 10 wk overlaid by FMG inoculation at 22 wk; and 4) 6/85MG at 10 wk overlaid by FMG at 45 wk. Two birds per isolation pen (experimental replicate unit) were necropsied at the end of both trials to observe the effects of treatment on liver weight, liver lipid and moisture concentrations, incidence of fatty liver hemorrhagic syndrome, ovary weight, mature ovarian follicle numbers, and the total and segmental weights, lengths, and histologies of the oviduct and small intestine. The applied treatments affected only liver moisture. Liver moisture content was greater in birds vaccinated with 6/85MG at 10 wk alone or in conjunction with FMG at 45 wk in comparison with sham vaccinated controls and birds that received a 6/85MG vaccination at 10 wk overlaid by an FMG inoculation at 22 wk. Prelay 6/85MG vaccinations may be a suitable substitute for prelay FMG inoculations, and FMG overlays during lay on prelay 6/85MG vaccinations may also provide continual protection against field-strain MG infections without eliciting any subsequent suppressive effects on performance, as noted in an earlier study.