Effects of S6-strain Mycoplasma gallisepticum inoculation at ten, twenty-two, or forty-five weeks of age on the performance characteristics of commercial egg laying hens.

Experimental inoculation of commercial laying hens, maintained under controlled conditions, with the S6-strain of Mycoplasma gallisepticum (S6MG) at 10 wk of age has previously been shown to affect the lengths and weights of various portions of the reproductive tract without affecting subsequent performance. Two trials were conducted to compare the effects of S6MG inoculation at 10 wk of age (prior to lay), 22 wk of age (onset of lay), and 45 wk of age (during lay) on performance characteristics in commercial layers housed and maintained under controlled conditions, as in previous studies. In each trial, BW, mortality, egg production, egg weight, eggshell weight per unit of surface area, percentage eggshell weight, percentage albumen weight, percentage yolk weight, and yolk weight per albumen weight ratio were examined at various ages throughout an entire laying cycle. Across wk 47 and 58 (age periods after the last 45 wk inoculation), eggshell weight per unit of surface area and percentage eggshell weight were significantly reduced in birds that had received an S6MG inoculation at 45 wk of age when compared with birds that had not received an S6MG inoculation or had been inoculated with S6MG at either 10 or 22 wk of age. Alterations in eggshell quality in response to S6MG may become evident only in older birds that are experiencing declines in production when housed under controlled conditions.