Efficiency and sensitivity of techniques for recovering nematode eggs from bovine feces.

Haemonchus contortus eggs were extracted from sheep feces and known numbers were added to helminthologically sterile bovine feces to provide samples with seven, 30 and 60 eggs per gram (epg). At 60 epg, dilution techniques (modified Cornell-McMaster and modified McMaster) tended to overestimate the number of eggs and more eggs were recovered (mean of 121 and 88% respectively) with these techniques than with centrifugal concentration procedures (modified Cornell-63% and Wisconsin- 69%). At 30 epg, all techniques were comparable (modified Cornell-McMaster 67%, modified McMaster 63%, modified Cornell and Wisconsin 64%). At 7 epg, the Wisconsin (61%), modified Cornell (60%) and Cornell-McMaster (94%) techniques were comparable and better than the modified McMaster technique (16%). At all levels of epg, the modified Cornell and Wisconsin techniques recovered eggs from 100% of the samples. The Cornell-McMaster and modified McMaster techniques recovered eggs from 90 and 100% of samples at 60 epg; 40 and 100% at 30 epg; and 21 and 11% at 7 epg. With a gravitational concentration procedure, the Standard Vial, no more than 16% of the eggs at any level of epg were recovered and at 7 epg eggs were recovered from only one-half of the samples. Five gravitational concentration techniques were assessed over 66 to 490 epg. The Ovassay, Fecalyzer and modified Standard Vial techniques were comparable in efficiency (28%, 25% and 24% respectively), but the Standard Vial technique was less efficient (11%). Introduced into diagnostic parasitology was the concept of predictive values which is the proportion of samples that a technique correctly identifies as being negative for parasite eggs. At 7 epg this was calculated to be zero for the modified Cornell-McMaster, modified McMaster and Standard Vial techniques and 100 for the Wisconsin and modified Cornell techniques.