Further studies on the development and availability of infective larvae of bovine gastrointestinal trichostrongylids on pasture in eastern Nigeria.

The dynamics of pasture populations of infective larvae (L3) of Cooperia, Haemonchus and Trichostrongylus species were studied at Nsukka, eastern Nigeria, during April to November 1984. Six paddocks were contaminated artificially and one was contaminated naturally. Five of the paddocks, P1-P5, were sequentially contaminated with faeces of naturally infected cattle at approximately 4-6-weekly intervals. Paddocks P6 and P7 were repeatedly contaminated every 4-6 weeks artificially and by the naturally infected cattle, respectively. Larval development and survival occurred very readily during the wet season (April-October) but apparently ceased in November at the start of the dry season. Larval migration, however, occurred not only during the rains but also during the first 4 weeks of the dry season. Single contaminations during the rains quickly gave rise to single waves of infestation which also declined rapidly, in spite of the continuously favourable conditions for larval development and survival. The repeated contaminations produced three and four distinct and relatively short-lived larval peaks, respectively, with the first three peaks on both paddocks, namely the May, July and September/October peaks, being coincident. The four waves of herbage infestation on P7, which occurred at approximately 4-5 weekly intervals, were considered to have originated from four separate generations of the three trichostrongylids. However, Trichostrongylus sp. predominated in the first (May) peak while Cooperia and Haemonchus dominated the later peaks.