Effective Drenching Practices
Spring has sprung-ish. For the first time in many moons, the pastures have a bright green lustor, a situation the livestock are busy trying make the best of. It is amazing how the range responds with the seasons changing, even without much rain. Hopefully, the long term forecasts hold true, the heavens open up and we have to dig our pickup out of the mud at least 3 times this year.
However, sheep and goat ranchers also know that moisture in the spring and summer also brings on the dreaded internal parasite Haemonchus contortus, aka the Barbers Poll Worm. This parasite can be deadly, especially to spring-born lambs and kids. Lactating females are also extra susceptible to this parasite as their immune system is weakened by the stress of lambing/kidding and they often lack enough protein in their diet to feed their offspring and fuel a proper immune response to parasites.
Historically, dewormers were quite effective at killing Barbers Pole Worm. Ranchers could deworm the entire flock whenever they were in the pen (shearing, marking, weaning, etc) and manage to keep parasites under control. This strategy is imperfect but it is practical and manageable, and ultimately effective enough to prevent noticeable problems for many years. However, a lack of new products being developed and the buildup of resistance to the same anthelmintics that have been on feedstore shelves for 30 years has created a diminishing level of efficacy. Long story short, the parasites have started to gain the upperhand.
For the purpose of this article, I’ll focus on deworming practices that science has proven to control parasites and slow the rate of resistance development by the worms. Good parasite management is much more than using the right dewormer(s). Understanding the parasite lifecycle, when sheep are most susceptible, genetic selection, and pasture management are all part of the solution. That is more than what I can cover in this article, but I strongly urge all sheep and goat owners to take the time to learn as much as they can on this topic from various online resources. www.wormx.info is one of the best places to get this information, as this website is hosted and managed by a team of leading sheep and goat parasitologists.
The goal of deworming is to kill as many parasites as possible inside the animal. However, every time a dewormer is given, some worms survive, which are the potential foundation of a resistant population. At first, maybe the anthelmintic kills 99% of the worms and there are so few that live that they don’t repopulate very quickly at all. This very small number of resistant worms shed eggs out on a pasture and mix with non-resistant worms that are already out there – essentially we still have a susceptible worm population. But after repeated use with the same anthelmintics, over time 99% turns to 90%, then from 90% to 75% and so on. This may take years, but unfortunately it is a slippery slope. Sheep or goats will still show physical signs of improvement until dewormers are ~50% effective. If 50% of the worms survive drenching, they can pretty easily reinfect pastures and the animals that graze them and the problem will reoccur within just a few short weeks. At that point, the level of resistance in worm populations is very high, which renders a single product ineffective for years if not decades in the future.
In an attempt to keep the efficacy at 99% or better, it is advised that sheep and goats that have moderate to high worm burdens be treated with at least two dewormer products at the same time. Worms that one product doesn’t kill, hopefully get taken out by the other product. Each product should be given at the full dosage rate based on product label. Products should not be blended together but rather given using two separate drench guns. They typically don’t mix into a solution very well and inevitably you’ll give more of one product and too little of the other. The dewormers should also be from separate classes that don’t utilize the same active ingredient. Contact your veterarian for guidance on dewormer products and their chemical class.
Copper oxide wire particle (COWP) boluses are another tool to help increase the effectiveness of dewormers. Research indicates that a 2 gram COWP given at the same time as a dewormer will improve the effectiveness of the dewormer by actually making the worms more susceptible to the anthelmintic. Caution should be taken to limit the number of COWP treatments given to sheep as they can be more sensitive to too much copper. We typically only give COWP to sheep once per year and target the most at risk animals, spring lambing ewes/nannies and freshly weaned lambs/kids. There are several factsheets and educational videos online regarding this topic, but again it is always advised to seek veterinary advice.
In summary, proper animal health is paramount to a sustainable sheep and goat operation. Invest the time to educate yourself on this topic and employ practices such as fecal egg count monitoring or FAMACHA scoring to have the most effective deworming strategy. Internal parasites are the leading health issue for most grass based operations, specifically during wet years. An intergrated parasite management plan that includes a smart deworming strategy is the only way forward to limit resistance and to keep your sheep and goats healthy when confronted with parasites. Don’t let Barbers Pole worm suck the blood from your stock and the profits from your operation every time we get wet weather.
To provide feedback on this article or request topics for future articles, contact me at reid.redden@ag.tamu.edu or 325-657-7324. For general questions about sheep and goats, contact your local Texas A&M AgriLife Extension Service county office. If they can’t answer your question, they have access to someone who can.