Introduction
Forage-based sheep and goat production offers several potential benefits, including disease resistance, stress reduction, improved animal welfare, and minimized feed costs. However, gastrointestinal parasites pose a significant challenge in such systems. While effective dewormers can provide short-term relief, repeated and improper use has led to parasite resistance, resulting in the partial or complete failure of dewormers.
Parasite resistance occurs when a dewormer loses its ability to effectively kill worms, allowing them to survive despite being exposed to therapeutic levels of the drug. As resistance becomes more widespread, producers face reduced treatment options. Therefore, it is essential to adopt integrated parasite management strategies that reduce reliance on chemical dewormers and promote sustainable parasite control. Flocks experiencing dewormer resistance must develop long-term management strategies to effectively control parasite populations.
Sheep and goats naturally harbor some internal parasites, and eradication is not feasible. The goal should be to maintain manageable parasite levels. Parasitic loads can be minimized through proper grazing management and by providing high-quality forages. Proper nutrition is essential for increasing the host animal's resilience to parasites, supporting health during infection, meeting production demands, and enhancing resistance to parasitic infections.
This guide sheet outlines the importance of forages and grazing management for controlling internal parasites in sheep and goats.
Survival of larvae in the pasture
The most common gastrointestinal nematodes in sheep and goats in the U.S. are the barber pole worm (Haemonchus contortus), the brown stomach worm (Teladorsagia circumcincta), and the black scour worm (Trichostrongylus colubriformis). The barber pole worm is more prevalent during warm, humid summer months, while the brown stomach worm and black scour worm are most problematic during the spring and fall.
Under favorable weather conditions (warm temperatures and sufficient humidity), parasite eggs can hatch and develop into infective larvae within 5-7 days (or up to 14 days at 50 degrees Fahrenheit). Larvae typically remain in the lower levels of vegetation to avoid UV radiation and desiccation, staying close to the ground where moisture is sufficient. When moisture levels are adequate, larvae may move toward the tips of the forage, otherwise, they remain closer to the ground. Moisture not only prevents desiccation but also aids in the movement of larvae, which can float on dew or rain on grass to be ingested by grazing animals. Larval density tends to be high within 12-24 inches from the feces and 2-3 inches vertically from the ground on leaf blades. Infective larvae float on moisture from dew or rain present on the grass, allowing them to be picked up by grazing animals. Consequently, the daily intake of larvae by the animals is proportional to the concentration of the larvae in the herbage on the pasture.
The infective larvae do not feed; they survive on stored energy and are most resilient in warm (65-85 degrees Fahrenheit), moist conditions. During colder months, strongyle larvae can survive the winter by either remaining as infective larvae in the top inch of soil and plant debris or by entering a hypobiotic state within the host animal's gut. Adult animals, especially periparturient ewes or does, can shed a new generation of larvae in their manure, posing a risk to young lambs and kids. Overwintered larvae can create heavy worm burdens in stressed ewes and lambs, leading to severe disease as early as mid-June or even earlier in the southeastern US.
Condensed tannin-rich forages
Condensed tannins are among the most widely studied plant secondary metabolites. They are present in various leguminous forages such as birdsfoot trefoil (4.8%), big trefoil (7.7%), sainfoin (2.9%), sulla (5.1-8.4%), and sericea lespedeza (4.6-15.2%) on a dry matter basis. Studies have shown that leguminous forages with high levels of condensed tannins (>3% DM) can reduce barber pole worm burdens in sheep and goats.
Sericea lespedeza, a high-tannin forage, has been scientifically proven to decrease parasite loads in small ruminants. This perennial, warm-season forage thrives in warmer climates across the U.S. and is well adapted to low-input, dry, and acidic soils. It contains high levels of condensed tannins, which contribute to its antiparasitic properties. Sericea lespedeza can be grazed, dried for hay, fed as leaf meal, or processed into pellets, offering flexibility in feeding strategies.
Research has shown that adult worms in animals grazing on sericea lespedeza shed fewer eggs, and the eggs that are produced exhibit reduced hatching ability. However, when animals are moved off sericea pastures and onto other forages, fecal egg counts increase again, indicating that mature worms were inhibited but not immediately killed. Long-term feeding of sericea lespedeza has been shown to reduce mature worm populations over time, making it an effective natural strategy for parasite management in sheep and goats.
After several years of research, the "AU Grazer" variety of lespedeza was developed. This variety features pliable stems, higher forage yield, abundant branching, and greater survival under grazing compared to other varieties. Sericea lespedeza can reduce both gastrointestinal parasite eggs and coccidia oocysts in feces, and it may also decrease the number of adult parasites in the stomach and intestines. However, producers should not rely on sericea lespedeza as the sole method for controlling internal parasites. Instead, it should be incorporated as part of a comprehensive parasite management strategy.
Multispecies grazing
Small ruminants and cattle, or small ruminants and horses, do not share most common gastrointestinal nematodes. As a result, strongyle larvae that are common to small ruminants typically die in the digestive tract of cattle or horses when consumed. Consequently, pastures grazed by cattle or horses tend to have a relatively lower number of infective larvae.
A study concluded that lamb growth rate, weight gain, and ewe production rate increased in an alternative grazing system (1 week of ewe grazing, followed by a 3-week rest period, and then 1 week of cattle grazing) compared to mono-species grazing. Additionally, alternative grazing systems have been shown to enhance ewe milk production, improve pregnancy rates, and reduce barber pole worm burdens in lambs.
Multispecies grazing or alternative grazing systems can be an effective means of parasite control as long as Trichostrongylus axei is not a major parasite in the host species, as this parasite is shared between cattle, small ruminants, and horses. There have been some reports of Ostertagia ostertagi from cattle infecting sheep and goats, and Haemonchus contortus from sheep cycling in pre-weaned calves (without causing disease). Additionally, H. placei, which primarily infects younger cattle, can also infect sheep and goats. Therefore, precautions should be taken if H. placei is a dominant nematode in the pasture. Multispecies grazing with cattle and small ruminants (sheep or goats) may effectively reduce parasitic larvae, especially when using cattle aged two years or older.
Rotational grazing
Under warm weather and sufficient moisture, it takes approximately 4-5 days for barber pole nematode eggs to develop into infective larvae. At cooler temperatures (around 50 degrees Fahrenheit), this process can take up to 14 days. To minimize the risk of animals consuming infective larvae, the grazing period in a given pasture should be limited to less than 4 days, after which animals should be moved to a new pasture.
Infective larvae do not feed; they survive by relying on their body reserves. Heat and low humidity can increase the mortality of infective-stage larvae. The survival period of larvae can range from 30-35 days in tropical regions to more than 10 weeks in temperate areas. Due to shorter larval survival in the tropics, a rotational grazing system with 4 days of grazing and a 35-day rest period can be effective for parasite control. In temperate regions, 5 days of grazing followed by a rest period of more than 65 days is recommended.
Some studies suggest that a longer rotational duration (3 to 9 months) may allow a substantial reduction in pasture larvae. However, such long intervals can negatively affect forage quality and are often impractical.
To ensure most infective larvae from the previous grazing period have died off, animals should be rotated through multiple paddocks. Ideally, the total pasture area can be divided into 10 paddocks, with each paddock grazed for about 3.5 days. This approach allows for a 35-day rest period before animals return, effectively reducing larval contamination.
In situations where extended ungrazed periods are not feasible, cutting forages for hay between grazing intervals can help manage parasite loads. Alternating between hay production and grazing at least 2-3 times during the season optimizes forage use while minimizing infective larvae on the pasture.
Dung beetle
Macrocyclic lactones (such as ivermectin, doramectin, and moxidectin) are potent antiparasitic drugs that are effective against nematodes and arthropods. These commercially available drugs are largely excreted unmetabolized in the feces, which can negatively affect non-target dung-colonizing insects, including dung beetles.
Field studies conducted in various parts of the world have demonstrated that dung beetles can reduce the number of infective strongyle larvae on pasture by 30% or more. This reduction is attributed to the beetles' activity in breaking down manure pats.
Although the exact mechanism by which dung beetles reduce strongyle larvae is not entirely understood, it is likely that colonized manure pats dry out more rapidly than uncolonized ones. This accelerated drying process can result in larval death or make the larvae more susceptible to consumption by microbes or soil nematodes.
Conclusion
Effective parasite control in sheep and goats requires an integrated approach, with grazing management playing a critical role alongside targeted deworming. Rather than relying solely on chemical dewormers, producers can adopt strategies such as rotational grazing, multispecies grazing, and incorporating condensed tannin-rich forages to reduce parasite loads and slow the development of dewormer resistance.
Implementing proper grazing management practices can help minimize animal exposure to infective larvae, thereby improving flock health and productivity. Additionally, integrating tannin-rich forages such as sericea lespedeza can further reduce worm burdens, while the presence of dung beetles and cattle in grazing systems naturally helps break parasite lifecycles.
Ultimately, a well-planned grazing system, combined with regular parasite monitoring (such as FAMACHA scoring and fecal egg counts) and strategic deworming, will support sustainable and profitable small ruminant production.
This article is made possible through NCR SARE professional development grant.