The worm burden of tracer kids and lambs browsing heterogeneous vegetation is influenced by strata harvested and not total dry matter intake or plant life form.

ABSTRACT

This study assessed the effect of total dry matter intake (DMI), plant life form and strata harvested on the gastrointestinal nematode (GIN) worm burdens of tracer kids and lambs browsing heterogeneous vegetation during the rainy season (August-November). The rainy season was divided into 6 2-week periods (P1-P6), and environmental conditions (rainy days, rainfall, temperature and humidity) were recorded daily. Five pairs each of tracer kids and tracer lambs raised free of GIN infections were used. Every 15 days, different pairs of kids and lambs were introduced to a 2.2-ha plot and co-grazed with a flock of 30 sheep and 70 goats for a period of 3 weeks. Feeding behaviour of each pair of tracers was measured in weeks 2 and 3. The continuous bite monitoring method was used to estimate total DMI, DMI of plant life forms and DMI from plants of different strata. After each 3-week period, the tracer pair was maintained indoors for 28 days and necropsied on day 29 to recover the worm burden. The feeding behaviour of the tracers was compared between periods (P2-P6) and between kids and lambs. The differences in the worm burdens of the tracers between periods were not associated with total DMI or DMI from plant life forms. Worm burdens were highest during P5 and P6 in tracer kids and lambs (P < 0.05), suggesting a build-up of infective larvae in the tropical deciduous forest (TDF). The lower worm burdens of tracer kids compared with lambs (P < 0.05) seemed to be associated with less low- and more medium-stratum ingestion.