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

摘要

Commercial laying hens maintained under controlled conditions were experimentally inoculated with the S6 strain of Mycoplasma gallisepticum (S6MG) at 45 wk of age. This resulted in depressed liver lipid concentration, and inoculations at 20 and 45 wk affected the size of various portions of the reproductive tract. In 2 consecutive trials of the current study, the effect of age of application of S6MG inoculation on the egg yolk characteristics of commercial layers similarly housed and maintained under controlled conditions was determined. The ages of inoculation compared were prior to lay at 10 wk of age, during onset of lay at 22 wk of age, and during postpeak lay at 45 wk of age. In each trial, yolk moisture and total lipid content were determined at 24, 32, 43, 47, and 58 wk of age. Yolk cholesterol concentration and yolk fatty acid profiles at wk 47 and 58 were also examined. Data from wk 24, 32, and 43 (effects of S6MG inoculations at 10 and 22 wk) and data from wk 47 and 58 (effects of S6MG inoculations at 10, 22, and 45 wk) were analyzed separately. The data of both trials were pooled then analyzed together. Across wk 47 and 58, percentage yolk lipid was significantly lower in eggs laid by birds inoculated at 10 wk compared with those inoculated at 45 wk. Sham-inoculated control and 22-wk inoculated groups had intermediate percentage yolk lipids. Compared with sham-control and 10-wk S6MG inoculation groups across wk 47 and 58, yolk myristic, oleic, and linolenic acid concentrations were reduced, whereas yolk stearic and arachidonic acid levels were increased by either 22- or 45-wk S6MG inoculations. In comparison with all other treatment groups at wk 47, yolk linoleic acid concentration was reduced by S6MG inoculation at 45 wk. Variable postpeak alterations in yolk total lipid and fatty acid content occur in response to the timing of S6MG inoculation in layers housed under controlled conditions.