Brady Campbell, Ohio State University sheep team

Managing parasites in small ruminants

By Matt Reese

The sun is out, the grass is growing and livestock in Ohio are out on pasture contentedly grazing. There is something special about the relationship between animals and pasture on a farm but there are challenges as well, including parasites.

“Worldwide, producers are losing billions of dollars to parasites through production losses and actual animal losses. They are more of an issue in the Eastern U.S. because our grazing areas are more concentrated than in the West. Issues with parasites increase this time of year when temperatures are 50 to 104 degrees F. Beyond this range, their survivability decreases significantly,” said Brady Campbell, program coordinator of the Ohio State University sheep team. “When it is hot, humid and wet they thrive. Now everything is out on pasture and when it is wet and dewy it is a problem. Dew is actually how the parasites travel up and down the forage and that is when the sheep are doing most of their grazing in the morning and evening.”

Small ruminants including sheep and goats are facing increasing issues with resistance to anthelmintics — dewormers —used for treating parasites.

Haemonchus contortus — the barber pole worm — is the most detrimental and difficult parasite to manage in small ruminants. Photo provided by Brady Campbell.

“There are several parasites for small ruminants but Haemonchus contortus — the barber pole worm — is the most detrimental and difficult to manage. It is a bloodsucker that causes severe anemia. It attaches to the abomasum, the true stomach. We get a decrease of nutrient uptake and get scarring and damage to the stomach. The animals are less efficient, especially the young animals, because they do not have an immune system developed,” Campbell said. “Anthelmintics kill the parasites, but when resistance develops those resistant genetics are the only ones passed on.”

The parasite situation for every farm is unique and needs to be managed accordingly.

“Every farm is different with different strains of parasites,” he said. “There is no silver bullet with management.”

Campbell is currently working on a number of different research projects looking at different angles of parasite management to address the challenges of resistance in small ruminants.

“Previously, the easiest way to manage them is anthelmintics, but we are seeing that continual use has led to anthelmintic resistance. The reality is that not every animal needs to be treated and the continual overuse of those products has led to resistant populations of parasites. If we get to the point where dewormers do not work we’re not able to save these lambs for example. You can also see losses in reproduction efficiency, decreases in wool quality and challenges with overall performance as well,” Campbell said. “There are only three drug classes. There are different trade names but only three drugs. We need judicious use in using anthelmintics, like using the FAMACHA technique to look at the lower eyelids. If we are just treating the animals that need it, it will help. Keeping records is important and tracking the genetic lines that have the most problems with parasites is important.”

When drugs are no longer viable management option, or there are efforts to maintain long-term efficacy of dewormers by minimizing drug use, different management strategies can be implemented. When working with sheep and goats, effective management requires an understanding of Haemonchus contortus.

“Understanding the life cycle of the parasites is important. If you do, one of the easiest management strategies is grazing and forage management. One thing we can do is rotational grazing. We suggest a three-day rotation cycle. The total life cycle for the barber pole worm is approximately 22 days. The animal will consume the infected larvae and then the larvae attaches to the abomasum and becomes reproductively mature in about 18 days,” Campbell said. “At that point the females begin laying their eggs. The female can lay 5,000 to 10,000 eggs a day. The eggs end up out on pasture in the manure.”

The eggs are resilient and do not hatch until the proper conditions are present.

“Eggs overwinter on pasture. They need a hot, humid climate to emerge from the oocyte,” he said. “They can also lay dormant in the animal for part of the year as well. The biggest time for shedding parasite eggs is at birth because that is a stressful time for the animal. Then these parasites thrive in hot, humid weather in the forage canopy.”

The time frame from egg to adult sets the basis for grazing management.

“They can mature from egg to infective larvae in four days. If we only allow the animals to graze for three days in a particular area, the animals are moving before the eggs can become infective larvae,” Campbell said. “Grazing in one spot for anything less than three days is helpful. In some of our trials we are waiting anywhere from 21 to 36 days for the animals to come back to those pastures.”

Some breeds offer management options through natural parasite resistance.

“There are different sheep breeds with resistance — St. Croix, Texels, Katahdins. The parasite starts to affect them like other breeds and then their immune systems take over and they rid themselves of the parasites,” Campbell said. “A lot of those are down south where the parasites are worse due to the heat, humidity and environmental conditions.”

Parasites can also be addressed through species diversity on a pasture.

“Mixed species grazing can be beneficial as cattle help break the parasite cycle and they are good to graze after sheep because of that,” Campbell said.

Campbell’s research is taking a look at a number of separate and combined management practices.

“We’re looking at different combinations to see what works best. We are looking at delayed weaning too. Some of our research shows that lambs that remain with their mother to 120 days performed better than lambs weaned at 60 days and placed on pasture,” he said. “About half of the early-weaned lambs needed treatments of dewormer and delayed weaned lambs did not need any treatment at all. Milk has a bit of an anthelmintic effect. It coats the abomasum and does not let the parasites attach. Milk is a huge source of protein too. We know that stress reduction is effective in reducing problems with parasites. We are looking at fall lambing and alternative annual forages too for parasite control.”

High tannin forages including chicory, birdsfoot trefoil and plantain are natural anthelmintics. Some producers plant those forages heavily in one paddock and run their animals through every 21 to 30 days.

Tillage can be another tool in parasite control.

“One way we can really hinder parasites is by creating an anaerobic environment by tilling the ground over. We have completed one trial and we are doing more,” he said. “We also created a naïve pasture from converted cropland that has never had sheep on it before. We are going to compare that to permanent pasture that has been grazed by sheep for several years. We’re checking to see parasite densities. We are also trying trials that increase protein intake to help them cope with parasite infections.”

Another of Campbell’s studies is using an ear tag that monitors each animal’s activity, like a pedometer.

“We can monitor activity, steps they take and we can collect an external body temperature,” Campbell said. “We can tell if an animal is infected based on activity and body temp. These tags record the data throughout the day. We may be able to detect parasitism at an earlier point with these ear tags. Earlier detection could lead to lower production losses. Once they get clinical signs it is pretty bad. We can hopefully minimize losses that way.”

Another tool being used in Campbell’s research is an elutriator, basically a big filter. “We put forage samples in it and it can test the density of parasites on the pasture. Not many other people are doing that,” he said. “We are going to use that with our grazing trials and our naïve pasture to see what management practices have the biggest impact on parasitic density.”

Regardless of what strategy is being used on a farm, when adding new pastures and bringing in new animals, it is important to understand the history to prepare for the increasingly challenging future of parasite management.

“Be cautious about the animals you are buying and the parasite management strategy they have been on,” Campbell said. “Parasites are a huge problem in our industry. I want to help famers save animals and money. Hopefully some of this research can help do that.”


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One comment

  1. It got my attention when you said that sheep, goats, and other small ruminants face an increasing issue with resistance to dewormers that can treat parasites. With this in mind, I would assume that there must be a continuous approach to finding ways to keep goats and sheep free from parasites, lice, and other issues. I could imagine how important it is for sheep that have lice problems to be treated well with urgency.

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