Internal parasitism is one of the most challenging of health concerns in small ruminants.
Sheep and goats under most production systems in Missouri are subject to heavy exposure to internal parasites. Small ruminants are considered to be more susceptible to internal parasitism when compared to other species and resistance to available dewormers is also becoming widespread. ‘Worms’ (primarily Haemonchus contortus – called the barber pole worm), represent the greatest threat to successful and profitable small ruminant production. The barber pole worm attaches to the lining of the stomach and feeds on the blood of the host resulting in poor production, weight loss, anemia and possible death.
All animals in a herd can be expected to carry some level of parasite burden. It is impractical if not impossible for the producer to try to completely eliminate the presence of worms within a herd. Instead, the goal should be a ‘managed’ parasite burden at a level that has little impact on the well-being and production of the host animal.
Relying solely on the use of pharmaceutical dewormers to prevent overwhelming parasitism in small ruminants is a recipe for failure. Other techniques for combating internal parasitism must be implemented into the herd management plan and a more sustainable approach must be taken. The following suggestions can go a long way in decreasing worm burdens and the need for using pharmaceutical dewormers.
Don’t overgraze pastures: Animals grazing taller grasses or browse are less likely to ingest infective larvae.
Decrease stocking rate: Larvae generally migrate less than 12 inches from a manure pile. A stocking rate of 6-8 animals per acre decreases exposure to infective larvae.
Rotate pastures: Rotating to clean pastures before larvae have a chance to develop will also decrease exposure. Ideally, rotating once/week and allowing each pasture 90 days to rest before regrazing will eliminate the majority of exposure to infective larvae.
Cross grazing/haying: Grazing pastures with alternate species such as cattle or horses ‘cleans up’ infective larvae from the pasture. These larvae are species specific and die after ingestion by other species. Haying a pasture has a similar effect.
Select resistant stock: Select for individuals within the herd that appear to be more resistant to parasitism. Cull those animals that require the most frequent treatments.
Small ruminants require different dosages of anthelmintics and require more care in the proper administration of anthelmintics when compared to other species. Consider consulting with your veterinarian to implement an ‘as-needed’ treatment protocol for your herd. Herd-wide treatments, in effect, leave only resistant worms to mate and produce the next generation of parasites (theoretically all with resistance to the dewormer used). Also, work with your veterinarian in selecting dewormers that are effective when used in your animals based on fecal egg count reduction tests.
Darren Loula, DVM, is a large animal veterinarian at Fair Grove Vet Service in Fair Grove, Mo.
