Deadly Pastures

Our cows and sheep celebrated First Grazing Day in early May, their favorite day of the year, when they get their first taste of lush forage. I can tell it’s their favorite day by how animated they are. They leap in the air, kick their legs, and dash across the pasture with joyful abandon. I’m anthropomorphizing here, but I spend enough time with the animals to have a pretty good sense of their feelings. And on First Grazing Day they’re all feeling good.

But I have mixed feelings as I lead them to the grass. I love that they fertilize the pasture and that if I manage their grazing correctly, it might help sequester carbon. I love that they can turn sunshine into meat, a profound alchemy that still seems like a miracle.

Those pastoral scenes of sweet sheep grazing lush pastures hide a deadly reality though. Microscopic parasites lurk unseen on the stems of the plants, and in slime trails left by snails and slugs. There are more parasites than letters in the alphabet, but healthy sheep can co-exist with most of them. Two are the exception, causing sheep fatality or permanent damage, and making a shepherd’s job much harder.

The barber pole worm, or Haemonchus contortus, is a stomach worm that sucks blood from the sheep, and in high enough density will kill an animal. Like all good parasites, this worm has also figured out how to use the sheep to distribute itself. Once comfortably lodged in the sheep’s rumen, it lays eggs which are shed in the sheep’s feces, hatch out and pass through several larval stages to be eaten by other sheep who are then also infected.

You’d think the animals are safe from worms once the pastures are covered in snow and the flock is all eating hay, and you’d be partially correct. But as we’ve learned through hard experience, the worms remain inside the sheep through the winter in a state of suspended animation. After the ewes give birth, the worms begin to wake up again, and can kill an animal before it even goes back out on pasture.

There are three ways we attempt to outwit the barber pole worm. One is by understanding its life cycle, and avoiding grazing the animals on pastures that are likely to have a high load of larva at the infective stage. We know that if we rest a paddock for 60 days between grazing periods, we can generally avoid the sheep ingesting this parasite. The second way is to keep the animals grazing high on a plant, as most of the infective larva reside in the lowest 4 inches of the stem. Grazing the animals through a stand of honeysuckle or other shrubs helps. The third strategy is to mix cattle in with the sheep, since they don’t share parasites. So a cow or steer can eat lots of barber pole worms without getting sick. Cattle function like sheep parasite vacuums in the pasture.

The other worm of concern is called deer worm, or P. tenuis, and as its name suggests, this parasite is transmitted from deer to sheep. The worm is carried by snails and slugs, who crawl over the deer poop, picking up deer worm eggs, and then spread them around in their slime trails. Sheep unwittingly consume them with the pasture, and when the eggs hatch, the larva lodge in the sheep’s nervous system. Usually the first sign of infection is an animal unable to move its back legs. If treated swiftly for 5 days in a row with a combination of dewormers and steroids, the animal still only has a 50/50 chance of recovery. In wet years, deer worm infection is more likely due to the flourishing snail and slug populations. The only way to prevent it is to prevent deer from accessing the pasture. Fat chance of that!

So, with a mix of joy and trepidation, I watch my sweet unsuspecting lambs enthusiastically tear apart blades of grass, and I think to myself, “I hope you don’t die this summer, so I can send you to butcher this fall!” Such is the emotional paradox of a livestock farmer.

7 thoughts on “Deadly Pastures

  1. Holy hell, that’s crazy! Maybe that’s why Aussie farmers run sheep in such dry locations? I had no idea. I reckon you need a flock of Blue Tongue lizards to wipe out your snail and slug population in the paddock before grazing. I’m sure Samson would happily manage your breeding program!

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    1. Hi Trav! We may not have Blue Tongues here, but we have ducks that love to eat snails. Friends of ours got a grant to assess the impact of running ducks ahead of the sheep in each paddock. For us, that proved to be way too logistically challenging, but I love the idea!


  2. full set up for microscope and slides is about 120 bucks and you can do your own fecals at home…this combined with a weekly 5 point check has helped keep our area flocks healthy….but I will also mention that there are always chronics in the bunch and that data can help you decide who to cull to strengthen your flocks overall health! Good luck these are relentless creatures


    1. We had just always used evasive grazing, and in 6 years with sheep I had only ever wormed a handful of animals. Last year we changed our grazing (shorter recovery early in the season), and we got *nailed* with worms, mostly because I wasn’t in the habit of doing FAMACHA every few weeks since I’d never really had problems, and also I had someone else doing most of the daily flock moves so I didn’t catch poor body condition or other indicators in time… farming is full of so many hard lessons!


  3. You have expressed it beautifully! Although we have not had any problems with deer worm, the barber pole is a nasty little creature and can so easily be deadly to sheep! I , too , have mixed feelings when we turn them out on pasture in the spring. It is so much fun seeing them kick up their heels with joy to have green grass again. Then the worry and rotations begin! I enjoyed reading this and certainly can relate. Thanks for sharing!


  4. Honestly, I’m not entirely sure how we’ve avoided these problems over the last 15 years, but I know that my wife throws pumpkins into the pastures every autumn. Maybe that helps? It also sometimes brings us new pumpkins the following spring, and the cycle repeats.


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