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MONITOR LAMB/KID WORM BURDEN

July 6th, 2009 · No Comments

Rory Lewandowski, Extension Educator, Athens County

July – September are critical times to closely monitor the internal parasite burden of lambs and kids. Preferably monitoring would start in June. The internal parasite of principal concern during the summer months is Haemonchus contortus, the barber pole worm. Lambs and kids grazing on pastures that are contaminated with large numbers of infective Haemonchus contortus larvae can go downhill very rapidly in July and August. It would not be uncommon that within a 7 to 10 day period a lamb or kid could go from a perky animal with energy to bounce around a pasture to an animal that is on the threshold of death, lethargic and with little energy to move about. Unless an effective rescue treatment is applied at this stage, the chance of survival is very low.

I sometimes hear sheep and goat owners say that parasites are not a concern to them because they are using rotational grazing or because they have an effective chemical deworming schedule. Neither of these strategies is going to totally prevent high worm burdens from accumulating or do away with the need to monitor lambs and kids during the critical July – September period.

Although rotational grazing is a good strategy to manage pasture health and provide quality forage, it does not prevent Haemonchus contortus from building up to very high levels on pasture. Let’s do a brief review of the life cycle of the worm during the grazing season. Adult worms attached to the stomach of an infected animal lay eggs that are passed in the animal’s feces. Under the favorable temperature and moisture conditions that exist in most summer pastures, eggs hatch to the infective larval stage in 4-7 days. Newly hatched larvae remain near the fecal pellet and pass through 3 stages of larval development termed L1, L2 and L3. The L3 stage is termed the infective stage because this larva will climb up blades of grass and wait to be ingested by grazing animals. Once the L3 stage has been ingested, it molts into an L4 larva stage and then molts in to an immature adult. When adults reach about 14 days of age in the stomach of the infected animal, they begin laying eggs. The entire life cycle from egg to egg can occur in as little as 24-25 days.

In a recent conversation with Dr. Shulaw, an OSU Extension Veterinarian who has considerable experience working with this problem of internal parasites, I asked about the life span of an infective Haemonchus contortus larva on pasture. Dr. Shulaw replied that L3 larvae can live up to 90 days on summer pastures given our climate and general pasture conditions. So, within the grazing season if a pasture is being re-grazed within that time frame and assuming our ewes and does were shedding Haemonchus contortus eggs in their feces on the first grazing pass, then those larvae are there waiting to be consumed in subsequent grazing passes. Since a mature female Haemonchus contortus worm can lay up to 5000 eggs/day, it does not take long for a pasture to accumulate very high levels of infective L3 larvae.

Depending upon chemical de-wormers and a regular deworming schedule is, at best, a short term fix. By now, sheep and goat owners who are serious about long-term production know that chemical resistance is an issue and that there is documented parasite resistance to all classes of currently available chemical dewormers. No chemical dewormer is 100% effective. Used repeatedly over time, the chemical will loose its effectiveness as the percentage of worms resistant to the chemical increase in the worm population on the farm. It’s important to understand that every time a chemical de-wormer is used, there is some selection for resistant worms. Deworming every animal in the flock or herd on a regular schedule is a formula for developing a resistant worm population and chemical failure. Selective deworming of only those individuals that really need some help will help to sustain the effectiveness of a chemical dewormer. That brings us back to the opening statement that animals need to be monitored.

How should lambs/kids be monitored during this critical period? There are two main tools that livestock owners can use; the FAMACHA eyelid score system and fecal egg counts. Both require time and regular application to be effective. Since few producers have the time, expertise and equipment to do fecal egg counts, they will have to depend upon their local veterinarian. The local vet may not have the time and/or staff to get fecal egg counts done in a timely and consistent manner and producers may not want to fork over $10 to $15 per fecal egg count test. That leaves the FAMACHA system.

The FAMACHA eyelid color score system uses a scale of 1-5 to grade eyelid color. The color of the lower eyelid is correlated with anemia caused by Haemonchus contortus burden within the animal. A chart with eyelid color and scores is matched to the live animal’s eyelid color. A bright red color score of 1or 2 indicates low levels of anemia and pale pink to white (scores 3-5) increasing levels of anemia. Generally an animal scoring a 3 or higher would be treated with an effective chemical dewormer. The value of the FAMACHA system is that it allows animals that are most affected by Haemonchus contortus to be identified and selectively treated without using a chemical dewormer on the entire herd/flock.

The most effective use of the FAMACHA system is consistent, regular application. During the critical July- September period, this means checking lamb/kid eyelids every 7 to 10 days. Keep track of scores for individual animals and use this as a record to notice trends that are developing. This is advice that was learned the hard way and here’s the story.

In 2008, I was involved in a small on-farm research project examining early weaning and pasture management to try to control Haemonchus contortus infection levels in lambs. Lambs were FAMACHA scored on a regular basis beginning in May. Towards the end of June over 90% of the lambs were scoring a 1 or a 2 and I thought parasites might not be a big issue. Then, doing FAMACHA scoring on July 8, over 40% of the lambs had to be treated with a chemical dewormer based on FAMACHA scores and backed up by high fecal egg counts. How did the situation change so quickly?

Ever notice how once something goes wrong you have time to go back and correct the mistake or take the time to think through what led to the error? We went back and looked at the FAMACHA scores and Dr. Shulaw did an analysis of FAMACHA percentages over time in the study. Here are some of the results: May 5: 77% of the lambs scored a 1, 23% scored a 2. June 5: 36% of the lambs scored a 1, 64% scored a 2. June 23: 29% scored a 1, 65% scored a 2, 5% scored a 3 and 2% scored a 4. July 8: 9% scored a 1, 42% scored a 2, 42% scored a 3, 5% scored a 4 and 2% scored a 5. Notice the trend toward higher scores over time. The distribution of FAMACHA scores was changing. Once the scores were looked at from this perspective, it was clear that lambs did not go downhill as suddenly as we perceived. The information was there, and a warning bell was sounding. The FAMACHA system can be used as an early warning system, but only if it is used regularly, records are kept and then those records are looked at for trends after each scoring of lambs/kids.

The last point I need to make in this article is that a farm needs an effective chemical dewormer to serve as a rescue option. How do you know if your chemical dewormer is effective or if resistance is developing? One way is by examining worm egg counts in the manure of treated animals, but this involves sampling relatively large groups and having your veterinarian do quantitative egg counts. Another way involves collecting some representative fecal samples and then exposing the eggs to the various chemical dewormers. One such assay is called the DrenchRite assay and is performed by a lab at the University of Georgia. The cost of this test is about $400, but resistance to all three chemical dewormers is evaluated on one composite sample. This makes this method very attractive for small flock/herd owners, and the assay results are available in about three weeks.

Beginning in June, but especially in the July-September period, is a critical time to monitor lambs and kids for internal worm burdens. Livestock owners need to recognize that early season pasture management will have an effect on parasite burdens. If lambs and kids can’t be moved to a safe pasture or feedlot system, then monitoring by use of the FAMACHA system, combined with an effective chemical dewormer, can help to reduce lamb/kid mortality.

For more information about the FAMACHA system or management of internal parasites, contact a member of the OSU Extension Sheep Team. Additional information about worm control and pasture management is also available on the Extension Sheep Team website at www.sheep.osu.edu .

Tags: Economics · Parasites

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