Gasbarre L C, Leighton E A, Davies C J
USDA, ARS, LPSI, Helminthic Diseases Laboratory, Beltsville, MD 20705.
Vet Parasitol. 1990 Nov;37(3-4):257-72. doi: 10.1016/0304-4017(90)90009-z.
Previous studies have indicated that host genetics significantly affects the number of gastrointestinal nematode eggs per gram (epg) in the feces of calves during their first grazing season. An entire calf crop of approximately 190 animals was monitored monthly until weaning to verify these earlier results, and to begin to discern the basis for this phenomenon. A significant genetic effect on fecal epg values was not observed until calves had been on pasture for 2-3 months, and was demonstrable until late in the grazing season when the effect was lost. The loss of a genetic effect coincided with the appearance of significant numbers of the more highly fecund nematode species Haemonchus placei and Oesophagostomum radiatum, and with an apparent increase in Ostertagia ostertagi transmission, indicating that the observed genetic control of epg values may be species specific, dose dependent or both. Calves were selected from the population, and grouped according to their epg phenotype over the grazing season as either high or low epg calves. Postmortem examination of some of these calves indicated that worm burdens in the low epg calves were 60% of those of the high epg calves. Experimental challenge inoculation of the remaining calves indicated that: (1) challenge with Cooperia oncophora resulted in low epg calves harboring worm numbers that were 65% of those of high epg calves; (2) challenge with O. ostertagi resulted in similar numbers of worms in both groups, but the fecundity of worms in the low epg groups was significantly lower (P less than 0.05) than in the high epg group. Analysis of serum anti-Ostertagia antibody levels in the grazing calf population showed rises in serum IgG1, IgG2, IgM and IgA antibody levels during the grazing season. Peak serum IgG2 and IgG1 anti-Ostertagia antibody levels were found to be significantly affected by host genetic factors while IgA and IgM levels were not under such control.
先前的研究表明，宿主遗传学显著影响犊牛在首个放牧季节粪便中每克胃肠道线虫卵（epg）的数量。对大约190头犊牛组成的整群牛每月进行监测，直至断奶，以验证这些早期结果，并开始探究这一现象的基础。直到犊牛在牧场放牧2至3个月后，才观察到对粪便epg值有显著的遗传效应，并且这种效应在放牧季节后期一直存在，之后才消失。遗传效应的消失与大量繁殖力更强的线虫种类——巴贝斯虫和辐射食道口线虫的出现相吻合，同时奥斯特他线虫的传播明显增加，这表明观察到的epg值的遗传控制可能是物种特异性的、剂量依赖性的或两者兼有。从牛群中挑选出犊牛，并根据它们在放牧季节的epg表型分为高epg犊牛或低epg犊牛。对其中一些犊牛进行的尸检表明，低epg犊牛体内的蠕虫负荷是高epg犊牛的60%。对其余犊牛进行的实验性攻毒接种表明：（1）用牛食道口线虫攻毒后，低epg犊牛体内的蠕虫数量是高epg犊牛的65%；（2）用奥斯特他线虫攻毒后，两组的蠕虫数量相似，但低epg组蠕虫的繁殖力显著低于高epg组（P小于0.05）。对放牧犊牛群体血清抗奥斯特他线虫抗体水平的分析表明，在放牧季节血清IgG1、IgG2、IgM和IgA抗体水平有所上升。发现血清IgG2和IgG1抗奥斯特他线虫抗体的峰值水平受宿主遗传因素的显著影响，而IgA和IgM水平则不受此类控制。
