Faecal worm egg counts and differential larval counts are a guide to the parasite burden. The number of helminth ova passed per gram of faeces depends on such factors as faecal consistency and bulk, host resistance, stage of pregnancy, effects of lactation and whether the worm burden consists of sexually mature parasites.

Faecal egg counts are generally lower from cattle than from sheep. If sheep are starved for 24 hours, the count may be increased. Inappetence may cause the count to multiply 30 to 40 times. Diarrhoea depresses the egg count.

Any statement of 'significant figures' for ova counts will be only a rough guide. Interpretation must be considered in relation to the specific parasite responsible (as indicated by larval cultures) and the age, origin, state of nutrition and clinical history of the infected animals.

For further information
Agnote - WormTest for livestock and guide to egg counts

Sheep

An egg count of 500 eggs per gram (epg) is generally considered high enough to require treatment in order to limit pasture contamination and subclinical disease. The following numbers of epg may indicate clinical disease due to that parasite.

Guide to faecal egg counts in sheep (indicating pathogenic burdens)

The egg laying capacity of Ostertagia spp. and Nematodirus spp. is poor and severe clinical signs may be seen before appreciable numbers of eggs are present in the faeces.

Low and medium egg counts will be more significant where the stocking rate is high, when weather conditions are conducive to epidemics (warmth, rain, humidity) and where the biotic potential is high, e.g. Haemonchus contortus.

Infections with one parasite only are rarely seen and the additive effects of mixed infections will require assessment. The pathogenicity of immature stages not indicated by egg count should always be considered. This is of particular significance with Nematodirus, Ostertagia, Chabertia, Fasciola hepatica and paramphistomes.

Dictyocaulus filaria is often associated with mixed gastrointestinal infections on the tablelands and slopes.

Cattle

The clinical history and knowledge of the seasonal pattern of worm parasites in different areas of the State will assist in interpretation of faecal egg counts.

In cattle greater than 18 months of age, the egg count gives little indication of the level of the parasite burden.

Guide to faecal egg counts in cattle (indicating possible pathogenic burdens in 6-18 month old cattle*)

Horses

600 epg or more may represent a pathogenic strongyle burden.

Colic induced by verminous arteritis from migrating Strongylus vulgaris larvae (without eggs in faeces), is not as common as in previous times.

Pigs

Any positive count of Ascaris suum ova in pigs up to 5 months of age is significant. Young pigs with heavy immature worm burdens may not be passing any eggs in the faeces. In infected pigs, eggs generally appear after the age of 9 to 10 weeks.

References

Cole VG (1986). Animal Health in Australia Volume 8, Helminth Parasites of Sheep and Cattle. Australian Agricultural Health and Quarantine Service, Department of Primary Industries, AGPS, Canberra.

Love SCJ, Hutchinson GW (2003). Pathology and diagnosis of internal parasites in ruminants. In Gross Pathology of Ruminants, Proceedings 350, Post Graduate Foundation in Veterinary Science, University of Sydney, Sydney;Chapter 16:309-338.

Skerman KD, Hillard JJ (1966). A Handbook for Studies of Helminth Parasites of Ruminants. Near East Animal Health Institute, Iran Unit, UNDP, FAO, Rome.

Smeal MG (1995). Parasites of Cattle, Veterinary Review No. 32, Post Graduate Foundation in Veterinary Science, University of Sydney, Sydney.