The epidemiology of gastrointestinal nematodes in goats in the traditional grasslands of Zambia

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Nalubamba, King Shimumbo
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Monthly faecal gastrointestinal nematode egg counts, coprocultures, differential larval counts and packed cell volumes of goats (according to age classes <6 months, 6 months to 1 year, 1 year to 2 years, more than 2 years) from two traditional farming areas (Chipembi and Shibuyunji) in Central Province of Zambia, were monitored over a period of 15 months from July 1994 to September 1995. The levels of infective gastrointestinal nematode larvae on pasture and monthly larval intake were also estimated using tracer goats. Each month, from September 1994 to August 1995, six goats, less than 6-month-old (tracers) shown to be free of gastrointestinal nematodes after anthelmintic treatment were grazed with a flock of naturally infected goats in Chipembi. After a month's stay, these tracer goats were removed, placed on cement-floored pens and were maintained in such helminth-free conditions for at least 3 weeks prior to necropsy and examination for adult gastrointestinal nematodes. Abomasa from the tracers were artificially digested to recover inhibited larvae. The faecal egg count pattern parallelled that of the total rainfall, being highest in the rainy season, and falling to very low levels during the dry season. The faecal egg counts from individual animals reached a peak in the middle of the rainy season (February, March) and lowest counts were observed from July to September. During all the months unfler study at least 80% of the adult goats had nematode eggs present in their faeces. Throughout the study period, goats less than one year old had faecal egg counts and prevalence which were significantly (P>0.05 ) lower than those found in more than one year old goats except during the rainy season when all animals * * were infected. Goats more than two years old had the highest intensity of infection as demonstrated by the higher faecal egg counts. Kids of less than six months revealed the lowest faecal egg counts and prevalence. The following species were identified on either postmortem worm count or by differential larval counts: Haemonchus contortus, Trichostrongylus spp., Oesophagostomum, Cooperia spp., Bunostomum spp., Trichuris ovis, and Strongyloides papillosus. Gaigeria eggs were also seen infrequently during the rainy season. H. contortus and Trichostrongylus were found to be the most predominant species observed, followed by O. columbicmum. Trichostrongylus peaked during the dry season while H. contortus and O. columbianum both peaked during the rainy season when temperature and moisture conditions favoured their development and transmission. Other nematode species revealed less defined seasonal fluctuations. Monthly larval intake of gastrointestinal nematodes was also monitored by the use of f tracers which indicated a high larval intake mid-rainy season up to the end of the rainy season. No larvae were picked up during the dry season. Inhibited larvae were only found in the months of December and May. Recommendations suitable for application in traditional areas, are made for the control of gastrointestinal nematodes.
Science-epidemiology of gastrointestinal nematodes in goats