EFFECT OF STRATEGIC GASTROINTESTINAL NEMATODE CONTROL ON FERTILITY AND MORTALITY OF NDAMA CATTLE IN THE GAMBIA

A large-scale longitudinal study was undertaken to investigate the eff ects of a strategic treatment of gastrointestinal nematodes on the mor tality and fertility of N'Dama cattle under village conditions. Initia lly, 1046 animals from 26 private N'Dama cattle herds, were monitored from October 1989 to December 1994. Each herd was stratified by age an d the animals were randomly allocated to two groups with a similar ave rage age. One group received a single anthelmintic treatment of fenben dazole (Panacur(TM), 7.5 mg/kg BW, Hoechst Veterina AG) in October 198 9, whereas the other group remained untreated. In July 1990, the herds were subdivided into two different treatment schemes. In the herds of scheme 1, the treated animals (Treatment group I) were treated once ( in August), whereas in the herds of scheme 2, the treated animals (Tre atment group II) were treated twice (in July and September). The same treatment schedule was used in the subsequent rainy seasons until Dece mber 1994. One group in every herd of both schemes served as control ( Treatment group 0) and received no anthelmintic treatment throughout t he study. The average annual cumulative incidence mortality between 0- 1 year was more than two times higher in treated animals compared to t heir controls (21% against 7.5%). No differences were found in older a ge categories. Survival analysis confirmed differences in mortality fr om 0-1 year, but were not significant in proportional hazard models. T he 25% quantiles of age at first calving was used to quantify differen ces between twice treated animals (50.2 months) and its controls (58.3 months) which represents a decrease of 8 months in twice treated anim als. Annual calving rates of twice treated animals were 52.2% compared to 43.6% in the control group (P < 0.001), which is an increase of 8. 6% to the control rate, Possible causes of increased mortality in 0-1 year old treated calves an discussed. We can conclude that in the pres ent epidemiological situation and the given parasite spectrum, gastro- intestinal nematodes mainly affect host fertility. Strategic control o f gastro-intestinal nematodes is thus recommended for young heifers up to their age of first calving provided the overall financial analysis of the intervention is beneficial. (C) 1997 Elsevier Science B.V.