Delayed resumption of development of inhibited Cooperia oncophora in a yearling calf

During a study of larval inhibition, resumption of development of Cooperia oncophora was observed in one calf to occur over a prolonged period of time. This animal had grazed for 14 weeks, was treated with thiabendazole and stabled for eight weeks prior to grazing the same pasture for ten days in late fall. A marked increase in Cooperia egg output started about six months after restabling. Worm egg outputs persisted for about 14 months with counts of up to 1000 eggs per gram during the first eight months of this period followed by a period with low counts of 50 to 150 eggs per gram.