Smith H J
Can J Comp Med. 1970 Oct;34(4):303-8.
A comparative study on the development of Osteragia Ostertagi, Cooperia oncophora and Nematodirus helvetianus in 15-month-old yearlings and three-month-old calves demonstrated that yearlings have considerably greater resistance to gastrointestinal parasitism than calves. This was manifested by the establishment of smaller worm burdens, marked stunting of worms and a markedly lower worm egg output in the yearlings. The characteristic marked rise in egg counts observed in calves a few weeks after exposure to a heavy gastro-intestinal parasite infection did not occur in the yearlings. It was concluded that fecal examinations have a limited usefulness as a reliable aid to diagnosis of gastrointestinal parasitism in older cattle.
一项关于奥斯特他线虫、牛古柏线虫和瑞士细颈线虫在15月龄一岁牛和3月龄犊牛体内发育情况的比较研究表明，一岁牛对胃肠道寄生虫感染的抵抗力比犊牛强得多。这表现为一岁牛体内的虫负荷量较小、虫体明显发育不良以及虫卵排出量显著较低。犊牛在遭受严重胃肠道寄生虫感染几周后出现的典型虫卵计数显著上升情况，在一岁牛中并未出现。研究得出结论，粪便检查作为诊断老龄牛胃肠道寄生虫感染的可靠辅助手段，其作用有限。
