“Through the years, I’ve watched numerous small ruminant producers go in and out of business simply because they couldn’t keep their animals alive,” Heather Glennon, Assistant Professor of Animal Science, University of Mount Olive, said. “Hopefully, if you can incorporate these five bullet points into your grazing system, you’re going to reduce the exposure of your small ruminants to worms through grazing management.”
Those bullet points, outlined in a recent USDA Natural Resources Conservation Services webinar presented by Glennon, focus on grazing management in order to regain control of parasites in the small ruminant herd.
“From the NRCS perspective, there is a lot of interest in doing more intensive grazing management plans for small ruminants,” Steve Woodruff, USDA-NRCS agronomist, said.
The top parasites of concern for small ruminants are barberpole (haemonchus contortous), hair worm, and brown stomach worm, with the barberpole worm being the primary parasite of interest. The larval stage known as L3 is the infectious stage of this worm.
Infected animals deposit the eggs in their feces, and within four to 10 days, the L3 larval stage emerges. This infectious larval stage can live for two months in very hot and humid weather, or up to six months in cooler conditions. Hot, dry conditions hasten its demise. In the L3 stage, the worms use moisture from dew or rain to crawl up stems of pasture forages, up to three inches above the ground. If this grass is then grazed by a susceptible animal, it becomes infected and the cycle begins again.
“Anywhere there is a humid environment, you’re going to have problems with parasites,” Glennon said. Parasites “steal the nutrition from the animals,” causing reduced growth, reduced milk production, decreased feed intake and feed efficiency, and increased mortality.
Symptoms of barberpole worm infection include: white eye membranes; bottle jaw – due to fluid accumulation; decreased weight; weakness; and sudden death. The worm feeds on the animal’s blood, causing anemia. It lays up to 10,000 eggs per day. With a significant anthelmintic (de-wormer) resistant populations plaguing producers, other options for worm control will play increasingly significant roles in maintaining herd health.
“If your animals aren’t getting proper nutrition… it can increase the infection and the effect on the animals,” and maintaining forage quality and grazing high are both important considerations, Glennon said.
Producers can incorporate a variety of grasses and legumes, both cool and warm season varieties, to enhance pasture potential. Using a combination of annuals and perennials can offer more options for intensively managing grazing behaviors.
“Each of them can play a role in managing your animals’ health,” she said of the variety of forage types available.
Increasing the height at which the herd grazes a paddock can combat infections. Tall fescue, orchard grass, bluegrass or rye grass are in a nutritious stage at a taller height. These grasses, grazed at eight to 10 inches in height for optimal quality, allow animals to be removed from pasture when forages are still four or more inches tall, significantly reducing the L3’s ability to infect animals.
Native warm season grasses are another option for tall grazing. These are grazed only to eight or 12 inches in height, are drought-tolerant, and palatable to small ruminants. Big Bluestem, Eastern gammagrass and Indiangrass are in this category.
Another way to graze higher is to use warm season annuals, such as pearl millet or sorghum-sudangrass hybrids, of sunn hemp, which provide a good quality forage as long as the stems don’t get too mature.
“If you use warm season annuals in your rotation, you are probably only going to graze them down to six or eight inches,” Glennon said.
Because planting annuals can involve disking or herbicide sprays, both of which cause soil desiccation, the parasites load is likely to be decreased. And, as these plants won’t be grazed for at least 45 days from planting, the survival rate of any remaining parasites in the field is reduced.
Decreasing pasture parasite load
Another means of reducing infestation from pasture is to remove the animals from the fields and practice periods of woodlot browsing. This method also provides shade, a benefit during hot summer days. Silvopasturing research has shown that browsing plants such as black locust, honey locust, mimosa and mulberry can provide needed nutrition, including 20 percent protein content from the trees, which exceeds maintenance requirements.
“This is actually what they would prefer to eat given the choice,” Glennon explained of the woodlot browsing. “The goats enjoy eating these things.”
Grazing cattle or horses alongside small ruminants, or following them, can also decrease the parasite load. These animals don’t share the same parasites, and the cattle or horses will graze and consume the worm eggs which cause small ruminant concerns. If one species follows another, the period of re-entry for small ruminants is increased, too.
Moving the animals to new pasture at least every three days, allowing paddocks to rest 30-45 days before regrazing, and controlling forage height are all benefits of a properly managed rotational grazing system. Unlike a continuous grazing system, rotational grazing systems control the forage type and height, and limit the time spent on each pasture.
“Balancing between getting the best forage quality and the parasite exposure at that point in time,” is the key to successful rotational grazing management,” Glennon said.
Taking a hay crop from a grazing pasture is another way to reduce parasite pressures. When making hay, the animals will be out of a pasture for a period of time until regrowth occurs. The process of making hay exposes eggs to the air and sunlight, decreasing parasite survival.
Tannins in the diet can increase protein efficiency, decrease bloat, and decrease the parasite load. Tannins, in concentrations greater than five percent, can cause palatability issue and interfere with rumen microbial functioning. Research has shown the effectiveness of sericea lespedeza in reducing parasite loads when fed at 50 percent of the dry matter intake, and is ongoing for birdsfoot trefoil, both of which contain tannins.
Enhancing the nutritional quality of the diet can readily be achieved by increasing the protein content of forages. A better diet provides increased resilience when a disease challenge occurs. Fertilizing at the recommended rates, feeding forages before they are too mature, and adding legumes to pastures will all benefit forage nutrition. Legumes will also decrease the need for added nitrogen application, while providing increased weight gain per acre for the animals, Glennon said.
The entire herd should not be dewormed at once. Selectively deworming the most vulnerable animals can help to decrease drug resistance in the parastic population. By leaving some animals untreated, non-resistant parasites have the opportunity to reproduce. This may eventually increase parasite susceptibility to the dewormers, making them more effective as a tool.
“If we can keep a population of parasites in the pasture system that are not resistant to chemicals, and they are able to breed with the resistant nematodes, then we will have some shot” at maintaining the effectiveness of dewormers, Glennon said.
Managing forages is a first line defense in controlling reduced production and mortality due to parasite infestations in small ruminant herds. Better grazing management offers parasite control via a variety of pathways.