Prolonged suppression of trichostrongyle egg output of N'Dama cattle by a single larvicidal treatment

Gambian village cattle herds were treated with a single dose of ivermectine (Ivomec, MSD-AGVET Inc. 1 ml/50 kg body weight) during the dry season. This treatment suppressed the trichostrongyle egg rise prior to the rains and led to delayed egg production for at least 6 months after the onset of the rainy season, compared to untreated animals from neighbouring villages. However, the results clearly indicate that a single treatment with ivermectine during the dry season does not lead to complete suppression of the gastrointestinal strongyle infections, since a worm population still gradually built up. During the second year the ranked level of the egg excretion was significantly lower than that of the control group throughout the year until December, except in August. The results further support the hypothesis that trichostrongyle reinfection is unimportant during the dry season in this climatic zone.