On the development of gastrointestinal parasitism in bovine yearlings.

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.