Comparison of two worm counting procedures for the enumeration of abomasal and small intestinal nematode parasites of sheep

Abstract

A comparison was made between two worm counting procedures in sheep. One involved the washing of the abomasa and first 10 m of the small intestine using a 250 μm aperture sieve. The other the processing of the abomasa and total length of the small intestine using a 38 μm aperture sieve. In the former case, the collection of worms and contents from the small intestine was performed by introducing water into the posterior end and then drawing it between finger and thumb, whereas in the latter instance the intestine was cut open before rinsing and washing. The data demonstrated that processing only the first 10 m of the small intestine was likely to result in a serious underestimation of the total numbers of worms present. They also showed that cutting open and rinsing of this organ was unnecessary if it had already been washed out by introducing water into it. The proportions of the total numbers of both 5th and late 4th stage worms recovered using a 250 μm aperture sieve were generally high. These ranged from 93 to 100% for all 5th stage worms and between 85 and 100% for late 4th stage larvae of worm genera other than Trichostrongylus where 45.8–61.5% of such larvae were recovered. However, only small proportions of early 4th stage larvae (range 7.7–33.3%) were retained by the use of a 250 μm aperture sieve regardless of the parasite genus involved. It is suggested that judicious application of these findings may enable considerable time savings to be made when performing worm counts in sheep.