Rory Lewandowski, OSU Extension Educator, Athens County
July and August are critical months to control the internal parasite, Haemonchus contortus in pasture based sheep and goat production. Often producers may find that lambs and kids seem to “stand still” during the summer, with little or no weight gain. There can be several reasons for this situation. One is that the nutrient level needed for good gains is not being provided, in other words, pasture quality is low. Another reason is that the animals have a parasite burden that prevents them from gaining weight. Finally, for those animals born in the February/March period, a natural immune response to internal parasites may be starting to develop. While this is important in the long run, this immune response exerts an additional nutrient demand upon the animal. In addition, the immune response can be overwhelmed by heavy parasite infections. In many cases, poor weight gain is a result of a combination of these factors.
Pasture management and monitoring of animals for parasite infection must be practiced as part of an internal parasite control strategy. The old saying, “know thy enemy” is appropriate since it is hard to make good pasture management decisions or know how to properly use monitoring tools without understanding the biology and lifecycle of Haemonchus contortus.
Haemonchus contortus survive and begin their life cycle each year through larvae that overwinter on pasture and/or through larvae “hibernating” in a process called hypobiosis in the abomasum of the host animal. This hypobiosis is actually an arrested development stage of the L4 larvae. In early spring, generally around lambing/kidding time, these L4 larvae resume the normal lifecycle, become adults and start laying eggs that are passed in the feces of the animal. So in the spring, adults and lambs can begin to accumulate Haemonchus contortus from consuming overwintered larvae, or from larvae emerging from newly deposited eggs.
Once an egg is deposited on pasture, if there is moisture and warmth, the egg hatches and a larva emerges, termed an L1 larva. Larvae need to go through a couple of growth stages to reach an L3 larva, which is the infective stage. L3 larvae migrate up and down grass blades in films of moisture. The time to go from egg to L3 infective larvae can be as short as 4 to 5 days under ideal temperature and moisture conditions. Once L3 larvae are ingested by grazing animals they travel to the abomasum or true stomach of the host animal. Larvae attach to the abomasum wall and begin to feed on blood. Within 2-3 days L3 larvae develop into L4 larvae and then adults. Once adulthood is reached, about 14 days are required before egg laying begins. The entire life cycle from egg to egg can be completed in as little as 21 days. Once egg laying begins, the female Haemonchus contortus can lay up to 5,000-10,000 eggs per day. As life cycles are completed, pastures can become heavily contaminated.
It is important to realize that the L3 infective larva can survive on pasture for up to 90 days in the summer, and up to 180 days when they develop in the fall. This obviously presents some difficulties in a rotational grazing system. For example, let’s say a pasture was grazed by ewes or does in October. This means that eggs being deposited at that time could result in some overwintered larvae still being around in April. By April ewes and does will have resumed shedding eggs, and in many years, pastures managed under rotational grazing are ready to graze by early April. New eggs are being deposited, infective larvae are being ingested, and here we go. By time that paddock has been rotationally grazed a couple of times, watch out! This is what would be termed a “hot” pasture. It might look like good green, succulent grass, high in quality, but it can be teeming with infective L3 larvae. Even a pasture paddock that started out more than 180 days removed from a previous season grazing pass can become a hot paddock after a couple of grazing passes with ewes, does, lambs and kids shedding eggs.
What are management options? They must revolve around trying to keep parasite levels low. Keep a pasture log/record of when paddocks were grazed and the length of time pasture paddocks were grazed. Start the grazing season on pastures that are likely to have very low levels of overwintered larvae. Rotate to a new paddock within a 5-day period to insure animals are not ingesting infective L3 larvae. A critical piece is to have some safe pastures that have very low or no parasite larvae on them to graze in July and August. This could be a pasture that has not been grazed since the previous fall, a paddock that might have had a grazing pass but then been allowed to grow for hay harvest, or a summer annual forage. Weaning time can also play a role in how pastures are used. Once a lamb or kid has been weaned from the ewe or doe, and the stress of lactation removed, the ewe or doe can tolerate some parasite infection. The females immune response provides some protection. So keep some safe pasture for weaned lambs/kids and then the ewes and does can go back and graze some of those pasture paddocks that contain infective L3 larvae.
The other management piece is monitoring animals. There are several tools available, including the FAMACHA eyelid color system and fecal egg counts. Both of these tools should be used on a consistent and regular basis to be effective. Used regularly, they provide trends that tell the livestock owner what is happening on the pastures and within the animal regarding parasite levels. Contact a member of the OSU Extension Sheep Team for more information about using these parasite-monitoring tools.
Notice that nothing has been said in this article about regular use of a chemical de-wormer. That is a road we don’t want to travel due to limited chemical options and big problems with parasite resistance to chemical de-wormers. Every sheep and goat farm that is serious about long-term production needs to know which of the chemical de-wormers, if any, work in their flock/herd and then save the use of that chemical for rescue treatments and selective de-worming as determined by regular monitoring.