Evaluation of the Cornell-Wisconsin centrifugal flotation technique for recovering trichostrongylid eggs from bovine feces.

Several variables in the Cornell-Wisconsin centrifugal flotation technique were studied using helminthologically sterile bovine feces to which known numbers of Haemonchus contortus eggs had been added. Neither mode of mixing (levigation versus conventional), volume (15-60 mL) of water used for making the feces water suspension nor specific gravity (1.20-1.33) of the sucrose flotation solution affected egg recovery. Optimal times for centrifugation at 264 x g of first the feces water and then the feces sucrose suspension were three and five minutes respectively. Under these conditions 62.6% of the eggs were recoverable and there was a linear relationship between the number of eggs recovered and those added to the feces. About 30% of the unrecovered eggs were found in the fecal debris retained on the strainer. About 5% of the unrecovered eggs were found in the supernatant discarded after the feces water centrifugation and also in the matrix of the viscous sucrose solution. Addition of the detergent Triton X-100 caused a decrease in egg recovery. False negatives were not encountered between 3 to 70 epg; at 1.44 epg there was only one in 14 samples. Optimum procedures for the technique are presented.