The consistency of faeces can bias the results of a worm egg count. The wetter the faeces, the lower will be the worm egg count relative to drier faeces, because the higher water content increases the faecal volume and dilutes the worm eggs. As a result, scouring animals will have artificially lower worm egg counts, that is, without the scouring, their WECs would be considerably higher.
The faeces can be scored for faecal consistency and then the worm egg count can be multiplied by the adjustment factor for that score to gain an adjusted WEC—the WEC that would be likely if the faeces were in a drier pellet-like state.
Very watery faeces (scouring, Score 3.5) may indicate a severe infection with scour worms. However, some animals may scour like this for short periods (generally only days to a week) when they are exposed to just a small number of scour worm larvae. This is called hypersensitivity scouring, and generally occurs once an animal has developed resistance to the worms, but has not been exposed to worm larvae for some months.
Animals may also scour for reasons unrelated to worms, the most common being a diet of lush green feed or the protozoan infection, coccidiosis.
The following images show varying faecal consistencies each with a score, as well as a multiplication factor.
Score the faeces before a WEC is carried out. Once the result is at hand, multiply it by the score, which is the adjustment factor, to gain an adjusted WEC (which is about what the WEC would be if the faecal pellets were discrete.
If you have a group of samples being tested together, either as a bulk count or as individuals, but with an average count calculated, give an average score for the group and then multiply the bulk or average result by the adjustment figure that matches the average score for the group of faeces.
Faecal consistency scores and WEC adjustment factors
Source: Leo Jambre, CSIRO
Adjustment factor: x 1
Faeces of this consistency is the standard and no adjustment to worm egg count (WEC) should be made.
Adjustment factor: x 1.5
To adjust the worm egg count for faecal consistency multiply the measured WEC x 1.5
Adjustment factor: x 2
To adjust the worm egg count for faecal consistency multiply the measured WEC x 2.
Adjustment factor: x 2.5
To adjust the worm egg count for faecal consistency multiply the measured WEC x 2.5.
Adjustment factor: x 3
To adjust the worm egg count for faecal consistency multiply the measured WEC x 3.
(If the faeces is extremely watery [more so than this photo], use a factor of 3.5)