Effects of supplemental dietary phytase and 25-hydroxycholecalciferol on the digestive and reproductive organ characteristics of commercial layers inoculated before or at the onset of lay with the F-strain of Mycoplasma gallisepticum.

In 3 trials, the effects of dietary supplementation with phytase (PHY) and 25-hydroxycholecalciferol (25-D3) on the digestive and reproductive organ characteristics of commercial layers that were inoculated prelay (12 wk of age) or at the onset of lay (22 wk of age) with F-strain Mycoplasma gallisepticum (FMG) were assessed at 58 wk of age. Experimental layer diets that included a basal control diet or a control diet supplemented with 0.025% PHY and 25-D3 were fed from 20 through 58 wk of age. As a percentage of total oviduct weight, magnum weight was lower in birds that were inoculated (sham or FMG) at lay onset compared with those that were inoculated prelay, and in FMG-inoculated birds, relative duodenum length was greater in those inoculated at 12 compared with 22 wk. Also, as percentages of organ weight or length, infundibulum length and isthmus weight were increased, whereas duodenum length was decreased by dietary supplementation with PHY and 25-D3. The overall timing (12 vs. 22 wk) of inoculation can affect the reproductive organ characteristics of layers, whereas, more specifically, the timing of an FMG inoculation may affect their digestive organ structure. Furthermore, independent of inoculation timing and type, the reproductive organ and digestive systems of laying hens may be influenced by dietary supplementation with PHY and 25-D3.