PhD theses have been written about worms, worm resistance to drench, sheep resistance to worms, and pasture management and drenching programs, so we'll only cover a very small bit of it here. Essentially, if you have a worm burden and sheep that have no resistance to worms, you need to drench. As a rule of thumb older animals have more resistance than younger ones (which start out with none), and cows have more resistance than sheep and goats. Worms are more of a problem when it's warmer and wetter, making spring and summer the real problem times of the year, although increasingly we see more issues with worms all year round, at least up here in the north. And Barber's Pole worm is an autumn problem, or has been in the past, now showing up more and more throughout the year.
Ok, so do you drench when you see dirty bottoms? Earlier? How long do you wait? And what drench to use. Well first of all, it's a good idea to chat with your vet about a worm control program. Each area and farm is different, both in terms of worm susceptibility and worm burdens. Your vet can guide you in which products to use when and why. They might even be able to supply you with just enough for your sheep and not have to buy a whole big container if you don't need it.
At Streamland we do a number of things:
- On the genetic side, we use the CARLA saliva test in our young rams and ewes to help us identify those that have more genetic resistance to worms. Breeding from these should help us develop a flock of worm resistant Suffolks. When we reach that goal there will still be animals that are susceptible to worms - it's not 100%. But we should achieve a much lower reliance on drenches and have healthier animals that do better.
- We also monitor our animals' worm burdens and drench regularly. Our basic drench is a combination drench. We use this during the spring and summer on our ewes. Our lambs receive a similar product with added tapeworm protection. They only need it once and then go on to the combination drench. When we are concerned about Barber's Pole worm (Haemonchus contortus), we use either a Moxidectin based product or a 3- or 4- way drench. Barber's Pole can kill a sheep very very quickly. The worm latches onto the stomach wall and sucks the sheep's blood, causing anemia. You see a sheep that doesn't really want to run around, maybe stumbles a bit, lies down like it's tired. Running it around is not a good idea. There isn't enough blood left in it's system to do any amount of exercise, and if it tries it will probably die of heart failure within a few minutes. Check the eyes and the gums - if they are white the animal is suffering from a severe Barber's Pole infestation. Leave it where it is and drench it with a product which lists Haemonchus contortus on the label. Then check the rest of them. Of course ideally you should also do fecal egg counts (take poo samples and send them to the vet to get the worm eggs counted - gives an indication of the worm burden). Unfortunately with Barber's Pole the worms have already caused a real problem before they lay eggs, so you can get anemic or dead sheep before your poo samples show eggs from Haemonchus.
So why worry about worms anyway? Well, unless you have resistant sheep (and lambs), worms (except Barber's Pole worm) will cause your sheep to scour. Scouring is too late because the gut damage is done, plus it results in dags. Dags attract flies, aside from being rather unattractive themselves! And flies means flystrike (yet another topic to write about). Your sheep will also lose condition and in the worst case die. It's just not worth it - if you have sheep you need to think about worms and do something about it. Talk to your vet about a good drenching program and about managing your worm burdens.