To Drench, or Not Drench

Dr. Reid Redden, Associate Professor and Extension Sheep and Goat Specialist, Texas A&M AgriLife Extension Service
(Reid’s Ram-blings: July 2021)

This spring was cooler than most and some were fortunate to get a good healthy rain. As things start to warm up, we expect to have problems with internal parasites in sheep and goats. Fortunately, there has been some advancements in technology to help in the fight against these pesky parasites. The bad news is, strategic treatment is not simple, and the more science learns about parasites, the more we realize just how much we don’t understand!

For me, the complexity of life is part fascinating and part frustrating. The intricate process by which sunlight and water grow plants that are eaten by sheep and goats to sustain themselves, grow, and reproduce is truly incredible. It is amazing how they overcome challenges and thrive in the face of adversity. Unfortunately, parasites, predators, and pathogens that negatively impact sheep and goats are just as complex and resilient.

Therein lies the dilemma: how we make decisions to better manage sheep and goats knowing there will always be drawbacks to every decision. Successful ranchers employ practices that result in the most benefit with the fewest consequences. Yet, best practices differ from one operation to the next and these best practices are constantly changing. The reason they vary between operation is because each ranch has different resources (labor, land, feed) and different overall management strategies (breed, season of birth, supplementation).

Parasite management is the best example of this. The barber pole worm (H. contortus) is the most damaging parasite to sheep and goats and is particularly problematic for certain animals: those that are thin, lactating, or young. Though the barber pole worm thrives in wet, warm, late spring conditions, it can still persist in most any animal and in any weather condition common in Texas.

For decades, ranchers administered de-wormer products repeatedly to prevent barber pole worm. However, treatment does not always eliminate every worm from the animal, with some resistant specimens surviving. These worms then reproduce at an alarmingly fast rate (10,000 eggs per day!) and before you know it, an entire population of worms resistant to the treatment you utilized has developed. Continuing to treat animals with the same products and tactics is eventually useless. Slowing the rate of de-wormer resistance is possible, but requires an understanding of the parasite, its lifecycle, and the animal’s immune system.

Simply put, there is no silver bullet to control parasites that will work for everyone. If someone tells you otherwise, they are misled, misinformed, or straight up lying. Strategic parasite management is a plausible solution, but this requires implementation of several strategies to mitigate the impact of internal parasites.

Parasite Management Practices Common to Texas Sheep and Goat Industry:

  • Fall or Winter Lambing/Kidding: Animals with compromised immune systems are most susceptible to barber pole worm. By shifting the birthing season to a time when parasites are not thriving because of less-than-ideal environmental conditions (for them, at least) your livestock may be vulnerable, but the threat of parasites is not nearly as high.
  • Combination Treatments: Providing 2 or more de-wormer products back-to-back improves the efficacy of treatment and prolongs development of resistance. Copper oxide wire particles may be part of the combination treatment.
  • Refugia: The process of leaving some animals untreated, while treating those who are in need, is called refugia, and allows for not at-risk animals to harbor parasites that aren’t resistant to the combination treatment. Eliminating barber pole from your herd/flock completely is not realistic, so if you are always going to have parasites in your sheep or goats, at least they are worms that can be sufficiently controlled with anthelmintics.
  • Genetic Selection: Some sheep and goats are more susceptible to barber pole worm than others; identifying and keeping those that have greater resistance as breeding stock can be a major piece of the puzzle. In brief, certain aspects of some animal’s immune systems allow them to naturally prevent parasites from becoming overly established in their abomasum. Fecal egg counting is a common way to estimate worm loads and a great tool for identifying potentially resistant animals. To help ranchers test their animals for parasite resistance, we have started a fecal egg count laboratory. Check out our website for more information.
  • Grazing Management: Barber pole worm hatch and develop outside of the animal, but are consumed when the animal grazes short grasses that the larva has crawled up on. The period from hatch to consumption by the animal can be as short as 4-5 days in ideal parasite conditions. Rotation of pastures before the parasites have developed is a great tool, however it requires the rancher to be set up for such. When grasses are taller (above 4-6”) or weather conditions are not suitable for egg hatching, having a longer rotation interval is OK. The key is, larva can survive on pasture for months, so not re-grazing the same area for a while is important for pasture rotation practices to be effective.

Employing a number of these practices on your ranch can help reduce both the economic and animal health related consequences brought on by internal parasites. Philosophically, it seems the “best” ranchers manage their land and livestock to maximize profit in good years and limit losses in poor years. Not to mention, they are lifelong learners who know that they have nothing completely figured out and relish the chance to incorporate new ideas and techniques. This spring has west Texas set up for a good grass growing season and livestock and their young should flourish… don’t let internal parasites ruin this opportunity!