Fecal Egg Counts for Internal Parasite Control:Assessing when sheep or goats need to be de-wormed can be difficult. Because of this, mistakes can be made and the use of anthelmintics (de-wormers) can be overdone. Excessive de-worming is wasteful, and it increases the chance for internal parasites to develop resistance to the de-worming products. The effectiveness of de-worming can be preserved by keeping de-worming to a minimum, compatible with profitable production standards. The information found on page B620 outlines parasite control programs that help prevent the build-up of parasite resistance and also identifies how a fecal flotation can be used.
What are Fecal Worm Egg Counts?: A fecal worm egg count is simply a count of the number of worm eggs present in each gram of feces from a sheep or goat. There are many different tests that can be used, with one of the most common being a McMaster’s fecal eggs per gram (EPG) test. Most of the tests are really quite simple. However, there are many steps where mistakes can be made if the procedure is not thoroughly understood. Regular practice is needed if eggs are not to be missed during counting. For these reasons, fecal worm egg counts are considered a laboratory procedure.
Collection of Fecal Samples: A reasonable and realistic sample of the flock or band needs to be examined before any confidence can be placed in a fecal egg count as a predictor of a parasite load. Fecal samples should be collected from a minimum of 10 (preferable more) individual sheep or goats selected randomly from the flock/herd. A misleading result can take place if only a few sheep or goats are sampled.
Fecal samples can be collected directly from the rectum of selected animals using a gloved hand. By far, this provides the most accurate samples, but requires the corralling of the animals and is distasteful to many people. Another procedure involves moving the sheep or goats to a convenient place in a pasture (a corner works) and holding them there for a few minutes. During this time, many will defecate allowing for the collection of fresh fecal samples. Care must be taken to avoid contaminating samples collected in this fashion with soil and plant material. To avoid contamination, gather pellets that are on top of the others and ones that have not contacted the ground.
No individual sample should be less than 4-5 grams. This is equivalent to a heaped teaspoonful of fecal material. Place the fecal samples into individually labeled containers. Small plastic bags are ideal. The samples should be kept cool, so immediately place them into an insulated container with a frozen ice pack. Do not freeze samples or refrigerate them for long periods (more than a day). They should be delivered to a veterinarian as soon as possible after collection.
When to use a Fecal Egg Count: Get an egg count done before the flock/herd is de-wormed. This will help determine if de-worming is necessary. Concentrate on young animals, weaners, and lactating animals. These animals experience the most worm problems. If it is determined that de-worming is necessary, a second fecal egg count should be done 10-14 days after the de-worming. If there is less than a 90% drop in the eggs per gram (EPG) between the first and the second fecal tests, there is parasite resistance to the de-wormer and a different product should be chosen. Ewes/does should have fecal egg counts performed shortly before lambing/kidding. Breeding males should have one performed prior to the breeding season. Lambs/kids should have a fecal test done just prior to weaning. Additional details on de-worming products and procedures can be found on page B620.
How to Interpret the Results: Each female worm in the gastro-intestinal tract of the sheep or goat lays eggs. These have to pass to the outside of the animal via the feces, before they hatch and develop further. In young animals, each worm lays many eggs and there is a direct relationship between the number of eggs passed in the feces each day and the number of female worms in the sheep or goat. Thus a count of the eggs can give an indication of the size of the worm load that is present. In mature sheep and goats that have been exposed to worms, the relationship between fecal worm egg counts and worm loads is less direct. This is because adult animals may have developed some immunity to suppress egg laying by the female worms.
Fecal worm egg counts of less than 400 eggs per gram (EPG) indicate the presence of moderate to light worm loads in a flock/herd. Therefore, a flock/herd average fecal egg count of less than 400 eggs per gram suggests that de-worming is probably not needed and will not likely produce immediate production benefits. If the EPG is greater than 1,000 in the spring or greater than 2,000 in the fall, a significant parasite load is present and de-worming is necessary.