Wet weather may trigger parasite problems for sheep/goat flocks

Writer: Steve Byrns, 325-653-4576, s-byrns@tamu.edu

Contact: Dr. Reid Redden, 325-653-4576, reid.redden@ag.tamu.edu

SAN ANGELO – West Texas along with much of the state, has been in various stages of drought for so long that sheep and goat parasite problems may be the last thing on a producer’s mind.

But with recent rains, stomach worms are likely to soon be a large problem for many flocks across the entire state, said Dr. Reid Redden, Texas A&M AgriLife Extension Service state sheep and goat specialist at San Angelo.

“Internal parasites, specifically roundworms and coccidia, can be among the most damaging problems for sheep and goats,” he said. “Most flocks have some level of parasitic infection but may never show symptoms until optimum conditions occur such as those we are experiencing now.”

Redden said during drought, parasites have a tough time surviving. Populations remain small and are rarely a problem. But when wet weather returns, parasites quickly get the upper hand and their populations explode.

“Stomach worms can actually stop their development inside the animal during adverse times and go dormant through a process called hypobiosis,” he said. “Then, when worm survival conditions improve during warm, wet weather or when the host animal’s ability to resist parasitic infection declines, such as during lambing, the worms suddenly get going again.”

Redden said the best control programs prevent parasitism prior to outbreaks. Dewormers or anthelmintics can enhance these control measures, especially when administered during hypobiosis before the eggs contaminate the pasture.

“However, misuse of anthelmintics can lead to resistant parasites. These drugs can be a powerful tool, but for long term-parasite management, dewormers cannot be the only preventative treatment,” he said.

Redden said the most damaging parasitic roundworm is the Haemonchus contortus or barber pole worm. When spring arrives, they begin to lay eggs, as many as 10,000 a day, spreading them across pastures through the animal’s manure.

The eggs hatch into larvae, and with the aid of wet weather, move from the manure to plant leaves where other sheep eat them, thus completing the life cycle, Redden said.

Affected sheep become anemic, lose weight, become weak and often develop “bottle jaw,” due to fluid accumulating under the jaw, Redden said. Though various levels of loss of production are the major economical losses, death of the animal from a parasite overload is not unusual.

“Genetic resistance in terms of the worm populations developing resistance to dewormers  is bad; conversely, resistance to worms within sheep and goat populations is good, ” Redden said. “Some sheep and goat breeds are more resistant to parasites, but even within other breeds, those genetic differences can be selected for.”

In general, Redden said animals most susceptible to stomach worms are new mothers with lambs during the first few weeks after birth, young growing animals and animals without prior parasite exposure.

If anthelmintics are used, he advises:

– Treat only the animals that need treatment. Routinely treating all animals can lead to  populations resistant to the class of dewormer being used. Leaving some parasites in the animals and on the pasture that are susceptible to the dewormer being used improves its effectiveness in later treatments. Treating only those animals that chronically need deworming also allows the manager to cull them in favor of more resistant individuals.

– Conduct fecal egg counts to determine if the dewormer is working. Doing so will also alert the producer that it’s time to switch classes of dewormers once a dewormer drops below an effective level. However, using multiple classes of dewormers at the same time should be avoided unless advised by a veterinarian.

“Should a parasite infestation get out of hand, it’s important to note that parasites cannot be spread in drylot conditions,” Redden said. “When large problems occur and dewormers aren’t working, pen the animals until the problem is under control.

“New Texas A&M AgriLife research has shown that feeding harvested juniper can reduce fecal egg shedding and improve the effectiveness of the anthelmintic ivermectin. Other high tannin-containing forages have been shown to produce similar results.”

Redden said the bottom line is that each property must develop its own parasite management plan, because no single program is appropriate for all operations. The plan should include a good rotational grazing management plan, smart drenching and attention to genetic selection.

“These protocols will differ from property to property based on environmental conditions, type of sheep or goat, flock management and past parasite exposure,” Redden said. “If questions still remain, it’s always best to consult your veterinarian or your county’s AgriLife Extension agent for specifics regarding anthelmintics and those management practices that will make their use the most effective.

“Rain is a good thing, especially here in dry West Texas, but it often comes at a price. As with most emergencies though, the damage can be lessened through preparation, management and a strong follow-up plan,” he said.

For more information, contact Redden at 325-653-4576, reid.redden@ag.tamu.edu.

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