In each of two trials, 80 commercial leghorn-type pullets were separated into two treatments with four replicates of 10 chickens in each treatment. Forty pullets were designated as controls and received no inoculation, whereas the remaining 40 pullets received the 6/85 vaccine strain of Mycoplasma gallisepticum (MG) at 10 wk of age. Hen-day egg production, egg weight, eggshell strength, Haugh unit score, pimpling incidence, and blood/meat spot incidence were monitored and recorded weekly in each trial through an entire laying cycle of 43 wk. Further, eggs from all treatments were collected daily, Monday–Thursday, and individually weighed.

No significant difference was observed between the treatments for 43-wk means for hen-day egg production, for any of the monitored egg or eggshell quality parameters, or for the number of extra large, large, medium, small, pee wee, or undergrade egg sizes. A significant (P ≤ 0.05) difference was observed for the number of jumbo-sized eggs between the two treatments.

Results of this study suggest that vaccination of commercial layer chickens at 10 wk of age with 6/85 strain MG does not detrimentally impact egg production, egg size distribution, or ovary/oviduct function as evidenced by selected egg parameters monitored in this study.