Successful Deworming Strategies

From egg counts to rotational grazing.

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Regardless of how you manage your animals, parasites should always be on your radar. Parasites are a significant cause of disease, lowered production, and high mortality among livestock. These problems create unnecessary economic loss, regardless of whether livestock are kept as a source of income or simply for family benefit, because treatment and replacement stock are more costly than preventative practices.

Successful parasite management is no longer a simple matter of grabbing the most convenient dewormer from the shelf. Due to widespread parasite resistance to nearly all dewormers, safe and correct deworming usage nowadays requires a multifaceted approach. To ensure you’re only using dewormers when necessary, utilize fecal sampling, selective deworming, and sound pasture management.

Evolving Deworming Strategies

Traditional wisdom has been to rotate dewormer medications, deworm on a schedule, and deworm each individual animal — no fecal tests required. Unfortunately, by following these practices, we’ve unwittingly exposed our livestock’s parasites to every single class of anthelmintic (dewormer) year-round. This constant exposure gave the parasites ample time and opportunity to evolve and “learn” how to resist practically all available dewormers. No new anthelmintics are in the making, hence the need for a new approach.

The most significant change required is the frequent use of fecal tests. Just as war commanders must know who their enemy is before they can attack, livestock owners must know what parasite has invaded their stock. Each species of animal has its own prime parasite. For goats, it’s the barber pole worm; for cattle, it’s the roundworm. But just because a species has a primary parasite doesn’t mean that’s the one afflicting your herd. Fecals will identify the specific parasites present, allowing you to better select a dewormer that targets those species.

At a minimum, a Fecal Egg Count (FEC) should be performed at least once each season, and a Fecal Egg Reduction Count Test (FERCT) should be conducted 10 to 14 days after administering a dewormer (see “Tips for Collecting Fecal Samples,” below). While the first fecal identifies the culprit, the follow-up fecal is an invaluable tool to determine the effectiveness of your chosen dewormer, because what works on one farm, or even for one animal, doesn’t work in every situation. Parasite resistance varies within a herd, since most animals tend to originate from different farms with varying exposure to dewormers. Most experts claim that the dewormer is effective if the levels of the targeted parasite are reduced by 90 to 95 percent from the fecal to when you complete the follow-up. They recommend selecting a different class of anthelmintics for the targeted species if the reduction in the percentage suggests resistance.

However, knowing your selected dewormer failed the FERCT isn’t enough information to guide you in selecting the next dewormer. When faced with resistance, it’s important to know which class the failed dewormer falls in, because resistant parasites will be resistant to every dewormer within that same class. Thus, you’ll need to select a dewormer from a different class that’s indicated for your specific animal and parasite. All anthelmintics fall into one of three main classes, each with a main active ingredient (see “Determine Your Dewormer,” below).

When you’ve chosen your next anthelmintic, be sure to administer it as soon as possible to ensure the last FEC is valid for the next FERCT. It may take more than a couple of attempts to find which dewormer works in your situation. Once you find one, though, you’ll know which medication to grab the next time it’s needed for that specific parasite. Just be sure to always conduct the FERCT to catch any resistance as early as possible.

Selective Deworming

Unfortunately, the prevalence of parasite resistance is so high that livestock owners must do more than just FECs and FERCTs. You must also be judicious in selecting which animals to deworm. One reason to choose carefully is that you’ll want some parasites that haven’t developed resistance to remain in your pastures and livestock. The theory is that allowing nonresistant parasites to remain will cause them to share their genetics with the resistant parasites, thus weakening their overall resistance over time.

This selective deworming may be accomplished in a couple of ways (although you’ll still need to use FECs to help make your selections). The first option is to select individual animals with possible genetic resistance to parasites. Generally, animals that are healthy, productive, have good body condition, and tend to maintain a low parasite load without deworming are often going to be the ones to select to not deworm. They’re also the animals you’ll want to breed in an attempt to bring those resistant genetics into your breeding program. But don’t wait to think about deworming until an animal becomes skinny, develops a shaggy coat, or goes off feed. Always conduct a FEC first, and then assess for possible resistance next. The primary goal is to keep your livestock healthy and productive, regardless of resistance.

You can also select animals for deworming based primarily on typical times of heaviest parasite loads, rather than deworming year-round. For instance, most livestock species experience higher FECs during early lactation or when very young, while older, well-nourished, nonlactating animals may be less likely to carry a high load, and as such are a safer selection for skipping the deworming when based on FECs. Also, depending on the livestock and the parasite you’re concerned about, deworming may be selected based on the seasonality of the parasite, as some parasites are more prevalent in winter, while others are more prevalent in cool, wet spring months. If taking this approach, carefully time your FECs to ensure you catch an accurate count to aid in your decision-making. Seasonal FECs are still recommended, as individual parasite loads may vary from season to season.

Healthy Livestock Housekeeping

Pasture management is the final aspect to using dewormers safely and with less frequency. Any feed that falls to the ground around feces and is then consumed is a prime source of parasitic contamination. Maintain feeders above ground level to help prevent this from happening. Water troughs need to be kept clean and filled with fresh water at all times to avoid animals drinking from feces-laden water.

Maintain a suitable height for forage whenever possible. Most experts recommend a height of 6 to 8 inches to help inhibit the parasites’ ability to climb to the tip and be consumed during grazing. Accomplish this with rotational grazing whenever space allows, and reseed as necessary to keep growth lush and tall. Keep stock off pasture until the forage is dry, as parasitic larvae require moisture to be able to travel to the tops of grasses. Because parasites won’t travel high enough on browse to be of concern, provide browsers, such as goats, with ample browse, and limit their grazing time to reduce parasite consumption.

Incorporating even a few of these practices will help reduce the overall parasite load of any species. In turn, you’ll help reduce dewormer usage and slow the development of parasite resistance. 

New Practices

Gone are the days of simply rotating dewormers on a schedule. Now, we’re faced with highly resistant parasites that our dewormers simply can’t kill.

The new plan of action for our farms should include wiser anthelmintic selection based on fecal tests, carefully choosing which animals to deworm, and incorporating better pasture management practices. And we should continue to research and study new methods, such as better nutrition, selecting naturally parasite-resistant animal species, maintaining lower stocking rates, and so much more in this battle against parasites. Incorporating as many facets as we can manage allows us to use our dewormers more safely and more accurately to keep our livestock healthy for years to come.

Determine Your Dewormer

Below are some of the popular anthelmintics on the market. Use this as a guide when deciding on the proper treatment for your livestock.

Benzimidazole Class

  • Albendazole (Valbazen)
  • Fenbendazole (Panacur; Safe-Guard)
  • Oxibendazole (Anthelcide)
  • Oxfendazole (Synanthic)

Imidazothiazole/Tetrahydropyrimidine Class

  • Levamisole (Tramisol; Prohibit)
  • Morantel tartrate (Rumatel)

Macrocyclic Lactone Class

  • Ivermectin (Ivomec)
  • Eprinomectin (Eprinex)
  • Doramectin (Dectomax)
  • Moxidectin (Cydectin)

Tips for Collecting Fecal Samples

Understanding the value of a fecal is paramount in using dewormers correctly. However, the information obtained from a fecal is only as good as the sample collected. Keep these pointers in mind when collecting that next batch of pellets, patties, or droppings.

  • Fresh is best. Manure found lying on the ground, in a feed trough, or in the hay bale should, in general, never be used. Parasite eggs hatch quickly in moist heat, making the Eggs Per Gram (EPG) inaccurate and useless in older, nonrefrigerated manure. Most labs request that only freshly deposited manure be used to ensure accurate test results.
  • Lube up. This may seem gross to some, but the best way to obtain the freshest manure possible is by very gently inserting well-lubed fingers into the anus of an animal to remove a bit of fecal matter. Alternatively, ask your local vet for a fecal wand to use instead of your fingers. Whichever tool you choose, make sure the animal is well trained for this approach, lest you end up with a hoof in the nose. Ask a mentor or veterinarian to first show you the process and let you know which species this method works best on.
  • Or, sit and wait. The preferred method by many — myself included — is to collect manure at feeding time. Most animals defecate readily during feeding, so keep a plastic zipper bag in your shirt pocket, with the intended target’s name and the date written on the outside of the bag. If you know your animals well, you’ll be able to detect when the dung is about to show itself. Position yourself in a safe position near the posterior and collect a nice warm sample as it drops out.
  • Keep it cool. Refrigerate the sample immediately upon collection to prevent eggs from hatching. If you’re in the field for a prolonged period, keep a cooler nearby with plenty of cold packs or ice. Then, seal up the sample and place it in the cooler. Just remember to never let the sample freeze, as this destroys the eggs.
  • Ship it or take it. If using a lab that requires shipment of the fecal, follow that lab’s shipping guidelines. Many require samples to be sent priority or overnight with a frozen cold pack or frozen water bottle to keep the sample cool. Double bag both the cold pack and the sample to avoid potential leakage in transit. While local vets may not require a cold pack, since transport times are generally short and eggs aren’t in danger of developing, ask first before leaving the house.

When collecting samples, check with your chosen lab first, as each lab varies in some of the details. For instance, some labs are OK with manure piles found in the field, while most insist on “fresh is best.” Still others have specific amount requirements, such as 1 to 5 grams, or simply “golf-ball-sized” samples.

Follow their guidelines, and the EPGs should be reliable based on their chosen systems.

Consider trying these labs for that next fecal:

More On Using Anthelmintics Wisely

Kristi Cook and her family have been building their homestead for many years in a quest for a more sustainable lifestyle.

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