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菌株（MG-F）可对鸡产生支原体感染保护作用，本研究通过血清学检测及气管组织病理学检查开展监测。试验共使用90只鸡只，分为3组：未接种对照组（G1组，30只）、8周龄时经眼滴接种MG-F疫苗组（G2组，30只，疫苗由巴西圣保罗州圣保罗的Ceva Animal Health公司提供）、8周龄与11周龄两次免疫组（G3组，30只）。分别于鸡只8、12、15、18、20及24周龄采集样本用于酶联免疫吸附试验（enzyme-linked immunosorbent assay，ELISA）检测；并于15和24周龄剖检时采集气管组织样本。
12周龄前，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，均低于0.20，组间无显著统计学差异（p > 0.05）。15周龄后，ELISA光密度值显著升高，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与G3组间无显著差异，但二者均与G1组差异显著。
各组初始体重（G1组592.71、G2组621.33、G3组594.40）、终末体重（G1组1932.58、G2组1987.59、G3组1875.20）及周增重（G1组11.65、G2组11.90、G3组11.14）均无显著统计学差异。
剖检大体气管评分方面，15周龄时各组均值分别为0.25、0.61、0.54，24周龄时为0.54、0.58、0.67，组间差异均不显著（p > 0.05）。显微镜下气管评分：G1、G2、G3组在15周龄时分别为0.25、0.32、0.47，24周龄时分别为0.07、0.75、0.08；其中G2组在24周龄时的评分显著高于G1与G3组。
相较于G1组，G2与G3组的气管病变程度更高，该差异可归因于MG-F感染。单次或两次接种疫苗未对活体重、增重及组织病变产生明显不良影响。