Recirculating elutriator for extracting gastrointestinal nematode larvae from pasture herbage samples

Authors: Cassida, Kimberly; Lester, Edward; Foster, Joyce; Turner, Kenneth

Submitted to: Veterinary Parasitology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/8/2012
Publication Date: 3/19/2012
Citation: Cassida, K.A., Lester, E.C., Foster, J.G., Turner, K.E. 2012. Recirculating elutriator for extracting gastrointestinal nematode larvae from pasture herbage samples. Veterinary Parasitology. 188(1-2):60-67.

Interpretive Summary: Control of gastrointestinal parasites in sheep and goats requires attention to levels of re-infection from ingested pasture forage, but existing methodology for measuring infective larvae on pasture samples is time-consuming and expensive. We designed and built an apparatus that quickly extracts larvae from pasture herbage samples and has a better recovery rate than previous techniques. This work is useful because better data on the impact of pasture management choices on infective larvae densities will help in selection of choices that can reduce infection. The work will improve profitability of sheep and goat producers, assist agricultural professionals in making informed recommendations, and benefit the public by improving animal health and reducing dependence on chemical wormers.

Technical Abstract: Gastrointestinal nematode parasites present an important limitation to ruminant production worldwide. Methods for quantifying infective larvae of GIN on pastures are generally tedious, time-consuming, and require bulky equipment set-ups. This limitation to expedient data collection is a bottleneck in development of pasture management practices that might reduce pasture infectivity. We modified a soil elutriator concept for extracting larvae from herbage samples. Elutriators were constructed from readily available parts and compared to the Baermann funnel sedimentation method for larvae extraction. More samples could be extracted per day in the elutriator than in a Baermann unit with extraction times of 4 min versus 24 hr, respectively. Maximum recovery of larvae seeded onto herbage samples did not differ between extraction methods (62.3 vs. 69.8% for elutriator and Baermann, respectively, P > 0.05). Larvae recovery from herbage in elutriators showed a strong loge relationship with extraction time (r2 > 0.97), which will allow development of accurate correction factors for specific herbages to predict total larvae densities at extraction times much less than those needed for maximum recovery. Extraction times of 4 to 8 min per sample gave the best compromise of speed, accuracy, and precision as measured by regression confidence bands and root mean square error of analysis of variance. Precision of the elutriator extraction for pasture samples was comparable to published methods and was not affected by forage species or canopy strata. The elutriator method was sensitive enough to detect differences in larvae density among pasture treatment factors. Elutriators extracted nematode larvae from herbage samples with accuracy and precision similar to existing methods, but did it much faster. Elutriation shows promise as an improved method for quantifying infective GIN larvae on pasture herbage.