Performance, serologic and tracheal responses of laying hens exposed to F strain of Mycoplasma gallisepticum

ABSTRACT: The F strain of Mycoplasma gallisepticum (MG-F) protects chickens against mycoplasma infections, in which monitoring is made by serology and histopathology of trachea. This trial used 90 chickens, being 30 unvaccinated (G1 group), 30 eye-drop vaccinated at 8 weeks of age with MG-F (Ceva Animal Health, São Paulo, SP, Brazil) (G2), and 30 immunized at 8 and 11 weeks of age (G3). Samples were obtained from chickens on the 8, 12, 15, 18, 20 and 24th weeks of age for the enzyme-linked immunosorbent assay (ELISA) test. Tracheal fragments were collected after necropsies on the 15 and 24th weeks of age. Up to 12 weeks, the ELISA reactions in optical density (OD) were 0.165 (G1), 0.151 (G2) and 0.151(G3), all below 0.20 and with no significant difference among groups (p > 0.05). After the 15th week, the ELISA reactions rose, yielding the following group averages by collecting dates: G1 (0.18, 0.19, 0.18, and 0.16), G2 (0.36, 0.49, 0.47, and 0.44) and G3 (0.41, 0.52, 0.59, 0.60), being the means in G2 and G3 not significantly different between than, but significantly different from G1. The initial weight (592.71, 621.33, and 594.40), the final weight (1,932.58, 1,987.59, and 1,875.20) and the weekly weight gain (11.65, 11.90, and 11.14) were not significantly different among groups. At necropsy the gross tracheal score means by group and dates were: 15th week (0.25, 0.61, and 0.54) and 24th week (0.54, 0.58, and 0.67), being these difference not significantly (p > 0.05). On microscopy, the tracheal score averages by groups G1, G2 and G3, respectively, were: 15th week (0.25, 0.32, and 0.47) and 24th week (0.07, 0.75, and 0.08). G2 yielded higher score average than G1 and G3 on the 24th week. Higher tracheal changes for G2 and G3 as compared to G1 could be ascribed to MG-F infection. There were no evident prejudicial effects on live weight, weight gain and tissue changes by applying one or two vaccination doses.

摘要：鸡毒支原体（Mycoplasma gallisepticum, MG）F株（MG-F）可对鸡产生抗支原体感染的保护作用，相关监测可通过血清学与气管组织病理学检测开展。本试验共使用90只鸡，分为3组：G1组30只为未免疫个体；G2组30只于8周龄时以眼滴方式接种MG-F株疫苗（由巴西圣保罗州圣保罗的诗华动物保健（Ceva Animal Health）公司生产）；G3组30只分别于8周龄和11周龄进行免疫。分别于鸡只8、12、15、18、20及24周龄时采集样本，用于酶联免疫吸附试验（enzyme-linked immunosorbent assay, ELISA）检测；并于15周龄和24周龄剖检后采集气管组织片段。
截至12周龄时，各组ELISA检测的光密度（optical density, OD）值分别为G1组0.165、G2组0.151、G3组0.151，所有数值均低于0.20，且组间无显著差异（p>0.05）。15周龄后，ELISA反应值出现升高，各采样时间点的组均值分别为：G1组（0.18、0.19、0.18、0.16），G2组（0.36、0.49、0.47、0.44），G3组（0.41、0.52、0.59、0.60）；G2组与G3组组间均值无显著差异，但二者均与G1组存在显著差异。
各组初始体重分别为592.71、621.33、594.40，终末体重分别为1932.58、1987.59、1875.20，周增重分别为11.65、11.90、11.14，上述指标组间均无显著差异。剖检后的大体气管评分均值（按组与采样时间划分）为：15周龄组分别为0.25、0.61、0.54，24周龄组分别为0.54、0.58、0.67，组间差异均不显著（p>0.05）。
镜检下的气管评分均值，G1、G2、G3组分别为：15周龄组（0.25、0.32、0.47），24周龄组（0.07、0.75、0.08）；其中G2组在24周龄时的评分均值高于G1组与G3组。相较于G1组，G2组与G3组的气管病变程度更高，该差异可归因于MG-F株感染。单次或两次免疫接种均未对鸡只活重、增重及组织病变产生明显不良影响。