Dr. Gareth Bath, University of Pretoria, South Africa, says when it comes to treating sheep and goats for internal parasites, producers have spent far too long concentrating on the parasites instead of the host.
“We tended to rely on dosing remedies that worked,” said Bath, explaining the worldwide resistance problem. “Since the 1960s, there have been a series of excellent drugs. Unfortunately, this led us to be lazy and get into bad habits and not think of anything except a dosing program. There is a long lag period between poor implementation of treatment practices and the problems that result.” Bath added that it might take five or 10 years to see the results of a poor program, and that’s where the silver bullet mentality occurs – thinking that there will always be a new drug to solve the problem.
But drugs, old or new, are not the answer. “Anthelmintic resistance has become rampant,” said Bath. “Many drugs are no longer effective against the worms we have. We need to change our attitudes and not just change drugs and hope that a new and better one is on the horizon.”
Sheep and goat producers have opportunities to increase numbers that will help meet the growing demand for product, but animals must remain healthy. Bath, who has extensive experience with sheep and goats, has some recommendations for parasite management. First, avoid blanket treatments of flocks and herds. “The worms that survive treatment are the resistant ones,” he said. “Slowly, they become dominant in the worm population.”
Avoid frequent treatments, which might work for a while, but become a recipe for eventual failure. Animals should not be treated during the ‘dry’ season (winter), when most of the worms are in the sheep. Bath urges producers to move away from fixed dosing programs and toward treatment programs that are tailored to the farm. Avoid estimating weights incorrectly — instead, treat according to the heaviest animal in the group.
Be careful of long-acting remedies, combination remedies and ultra-wide spectrum drugs. “These cover up the problem; often for decades,” said Bath. “Long-acting remedies work for a while, but they select for resistance. With combination remedies, by the time you discover you have a problem; you’ve lost the efficacy of two, three or more remedy groups all at once. You might want to treat for external parasites, and unwittingly also select for resistance.” Bath added that homemade concoctions that have only anecdotal success should be avoided.
Producers should to be cautious with generic products. “They’re supposedly the same as the original compound,” said Bath, “but are made by a different company. “They can be all right, but sometimes generics aren’t equivalent to the original compound.” When it comes to the latest or newest products, use with caution and save them for emergencies, quarantine or other purposes.
Bath suggests sheep and goat producers implement a holistic, sustainable program tailored to their farm, which he admits is not easy. He urges producers to initiate targeted, selective treatment. “Don’t treat all of the animals unnecessarily,” he said. “Treat the animals that will benefit from the treatment and leave some untreated so they retain some worms that haven’t been selected for resistance.”
Fecal egg counts can help monitor what’s going on in the flock or herd, but must be done properly. Fecal egg count reductions can determine whether or not a particular drug is working. Any sheep or goats introduced to the farm should be quarantined and treated. “When you introduce them, put them in an area where they won’t transmit eggs,” said Bath. “Then treat them vigorously. Make sure that all animals are properly treated and quarantined, then release them on your contaminated pastures so they pick up your sheep or goats’ worms and not the other way around.”
Bath, who helped develop the FAMACHA system, explains that many producers are now using the method that assess the inner eyelid for level of anemia, but adds that FAMACHA is only good for a few blood-sucking internal parasites. “FAMACHA has been in action for 15 years, and it really works,” he said. “It’s great for barbers pole worm, but what about the rest? We’ve expanded to a five-point check, which encompasses all of the worms of sheep.”
The five-point check includes looking at the nose for nasal discharge to determine whether treatment is needed for nasal bot fly. Check the inner eyelid for anemia and under the jaw for swelling (indicating barbers pole worm and/or liver fluke). Determine the condition score of the animal to assess nutrition level, and examine the animal’s back end for excess soiling.
Bath advises that because the herd sire is half of the herd or flock, sires should be selected based on FAMACHA scores – despite any other outstanding traits they may have. “Heritability for resistance is only about 25 percent, but that’s enough to make progress genetically in three years,” he said.” Females should also be selected for resistance. Bath urges producers to stop selecting sissy sheep – sheep that don’t hold up in a given farm setting – and to always leave the best and treat the rest.
“You must always give the animal a chance to develop immunity to parasites, and that comes with good nutrition,” said Bath. “The most important aspect of nutrition is protein. Animals that have enough protein are not as bothered by parasites. Minerals also affect immunity to parasites but are secondary to the need for protein. Watch animals for general health so they don’t become susceptible to parasites.”
In the face of heavy parasite pressure, Bath suggests reducing the length of time parasites can be consumed by an animal by having many small paddocks where animals can be rotated frequently.
If possible, decrease grazing pressure. Topography of the pasture can influence parasite levels: marshy land accumulates water and parasites, and thick clay soil that retains moisture is more favorable for parasites. South-facing slopes are drier with less risk of parasite survival. Bath emphasizes the fact that ‘clean dosing’ is not helpful because animals must be exposed to parasites in order to develop a degree of immunity to those parasites.
“You don’t have to try to do all things,” said Bath. “Choose which work for your farm and add as you can. Strive for a balance between the parasite, the sheep or goat, the environment and the farm and farmers. The key is to monitor effectively and often. We don’t say that you shouldn’t treat ever. We do say that when you treat, you treat in the right way, and treat the right animals.”