Faecal Egg Counts

Faecal Egg Counts
Faecal worm egg counts (FEC) and larval cultures provide a guide to the parasite burden. It is important to know when to drench stock and if the drenches are indeed working.

In an aim to minimise the development of drench resistance; the use of FEC provides information to determine if is possible to extend the drench interval.

FEC’s assess the number of worm eggs passed per gram of faeces; this depends on many factors such as faecal consistency and bulk¸ resistance, stage of pregnancy, effects of lactation and whether the worm burden consists of mature parasites. Immature worms and larvae do not lay eggs therefore quite large numbers of ‘young’ worms can be present in the gut causing damage before any egg count can be detected in the faeces.

Faecal egg counts are generally lower in cattle than in sheep. If sheep are starved for 24 hours, the count may be increased. Inappetence (lack of appetite) may cause the count to multiply by 30 to 40 times. Diarrhoea depresses the egg count.

Once a significant egg count is detected, a larval culture can be performed to identify which worms are present as the eggs of the likes of ‘Ostertagia.’ and ‘Cooperia.’ look identical. Different worms cause different levels of disease in the animal therefore in order to investigate a drench resistance problem knowing which worms are present and which are being killed by the drench is vital.

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. On some farms, where there is a high focus on growth rates, drenching at 350 epg is acceptable. This does not present any problems in terms of developing immunity in lambs or hogget’s. Very low worm burdens will be adequate to stimulate the immune response in young sheep.

The worm species ‘Ostertagia.’ and ‘Nematodirus.’ do not produce large amounts of eggs 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 and humidity) and where the disease potential is high e.g. ‘Haemonchus contortus’ (Barber’s Pole worm).

Infections with one parasite only are rarely seen and the additive effects of mixed infections need to be taken into account.

The FEC figures in cattle are not as straightforward as they are with sheep so it is important to consider the type of young stock and the clinical signs along with the FEC in order to decide if treatment is necessary. The clinical history and knowledge of the seasonal pattern of worm parasites in different areas will also 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. In younger animals especially 6 to 12 months old, the FEC does correspond to worm challenge and is useful for drench checking.

Collecting Samples
FECs can be performed on individual samples or pooled samples. Individual samples need to be representative and several need to be performed to give an overview of the situation; usually 6 to10 samples per group. In addition, sampling animals with loose faeces can lead to artificially low counts.

Pooled samples should be taken from 10 to 20 animals from the same group and these must be mixed well. For example when examining a group of ewes and lambs, one pooled sample should be taken from the lambs and a second from the ewes. A small amount (a single pellet or equivalent) from each animal is all that is necessary. This can be undertaken by standing in the paddock and collecting samples as the animals deposit them, or by running them into the race and collecting directly from the rectum. Pooled samples are not as accurate as multiple individual samples, but are a quick and easy method of collection and are less expensive.

Collection should be undertaken with gloves into a clean sample pottle. Samples should ideally get to the vet/clinic the day of collection so they can be at the laboratory that same day. FEC sample results will normally be through in 24 to 48 hours and cost $10 to $15 per sample depending on the number of samples submitted. Larval culture tests take 10 days and cost $104 per sample.

Date Added: Friday, 6th November 2015