2007 Annual Report 1a.Objectives (from AD-416) The objective of this cooperative research project is to determine the reproductive organ characteristics, blood composition, and subsequent eggshell microstructural characteristics in Mycoplasma gallisepticum-vaccinated egg-laying chickens fed various dietary supplements. 1b.Approach (from AD-416) Chickens will be monitored to determine the effects of MG infections and diets on various reproductive organ, blood, and eggshell properties, including the eggshell's microstructure. Light and scanning electron microscopes with digital imaging systems will be used to measure eggshell parameters such as total shell thickness, mammillary cone thickness, and columnar region thickness. Digital micrographs will also be taken to assess shell structural features including radial shell sections, shell membranes, and mammillary cones. The effects of diet supplements (poultry fat, phytase, vitamin D3) on MG-inoculated birds will be studied in several consecutive trials. 3.Progress Report This report serves to document research conducted under a Specific Cooperative Agreement between ARS and Mississippi State University. Additional details of research can be found in the report for the in-house project 6406-32000-008-00D, "Diagnosis and Control of Mycoplasmosis in Poultry." Methods used in monitoring activities covered under this project were meetings and telephone calls as well as research facility site visits. Research was conducted to determine the effect of vaccination of commercial layers with F-strain Mycoplasma gallisepticum (FMG) on eggshell quality and structure. In addition to vaccination, experiments included three different diets (basal diet; 2% poultry fat (PF) added; and 2% PF plus phytase and D3) and two ages of lay (24 and 50 weeks). Cross-section micrographs of eggshells were taken and thickness measurements were made. It was found that FMG inoculation may increase subsequent eggshell thickness at 24 and 50 weeks of layer hen age, but that this effect may be reversed in hens at 24 weeks of age by dietary supplementation with 2% PF.