UGA Forage Extension Team

Managing internal parasites through better grazing

By Adam Speir

Madison County CEC

Internal parasites can cause significant production losses in livestock, which results in significant economic losses for livestock producers. These parasites affect cattle, horses, sheep, and goats. Many times, the effects are subclinical and may go unnoticed, but severe infestations can cause disease and death. Subclinical effects caused by internal parasites include reduced milk production, reduced weaning weights, delayed puberty, decreased fertility and pregnancy rates, as well as reduced feed intake, diarrhea, anemia, and immune suppression. Because of the potential health and production impacts of internal parasites on livestock, proper planning and management is important. Livestock producers will often use dewormers, but many of these have lost their effectiveness due to resistance in the parasite populations. Aside from chemical control measures, other management strategies exist. This article will specifically address how good pasture management can help reduce internal parasite pressure on livestock.

Good pasture management related to managing internal parasites requires an understanding of the lifecycle and preferences of the most problematic internal parasites. Most of the problematic parasites we deal with are roundworms (nematodes) which have a direct lifecycle – meaning they require only one host to complete their lifecycle. For example, Ostertagia ostertagi (Brown Stomach Worm) is a common parasite in cattle while Haemonchus contortus (Barber Pole Worm) is the most common parasite of concern in small ruminants. Most internal parasites are host-specific, meaning that different livestock species often do not share the same parasite species. Cattle and goats or sheep do not share many of the same parasites, but sheep and goats will share the same parasites.

Mature parasites reproduce inside the host and eggs are released in the feces. These eggs hatch inside the feces. Warm, wet weather conditions are most favorable for egg hatching and larvae development. Once the larvae hatch, they travel up the blades of grass in order to be ingested by livestock while grazing where they will mature and begin reproducing, repeating the cycle. Larvae are able to travel 2-3 inches up the plant but could travel further under ideal conditions. In areas where fecal matter accumulates (near water & feed sources or shade) or where pastures are overstocked, parasite density will be high. When conditions are moist and warm, larvae will be more prevalent. In dry conditions, larvae stay close to the soil surface where there may be enough moisture to survive.

Understanding these concepts helps provide some important strategies to help manage pastures to reduce parasite pressure –

1)            Do not overstock or overgraze – Regardless of livestock species, overstocking pastures results in a variety of issues. Related to parasite management, overstocking will ultimately lead to shorter forages to graze and increases the likelihood of animals ingesting parasites. Maintain a healthy grazing height of your forages and work with your Extension agent to balance your animal stocking rate with available forages to reduce grazing pressure.

2)            Rotate Pastures – Rotating livestock through different pastures helps to reduce parasite pressure by removing animals before parasite eggs hatch and larva are ingested. For example, the complete lifecycle of H. contortus can be about 3-6 weeks, with the time of egg drop to larvae hatching within 4-5 days. If livestock are allowed to graze in a paddock for 3-4 days, and then rotated to another paddock, this keeps the animals from continuing to ingest parasite larvae. If conditions allow, keeping the livestock off that original pasture for 4-6 weeks can allow the parasite larvae to die and the pasture to be “clean” of the parasite larvae that originally hatched. The length of time it takes for parasite eggs to hatch and larva can depend greatly on temperature and moisture conditions. Parasites eggs can sit idly for a long period of time until conditions are favorable. While a lifecycle of 3-6 weeks is realistic during a humid summer in Georgia, that time could be extended by months during drought or cooler times of the year. To ensure that a pasture is totally “clean” of parasites, it should not have been grazed by livestock for 12 months, or the ground has been prepared for planting of a crop or utilized as a hay field.

3)            Consider Mixed-Species Grazing – As mentioned earlier, many common internal parasites are host-specific. This means that cattle can help “break” the cycle for sheep or goat parasites by ingesting them but not providing an environment where they will reproduce – the same is true for cattle and horses by bringing in sheep or goats. You can graze mixed species simultaneously, or alternate livestock species to achieve the same purpose. Grazing different livestock species can also achieve the goal of better utilization of different forage types and improved “weed” control.

4)            Incorporate Improved or Alternative Forages – Utilizing different forage crops such as legumes or summer annuals can provide higher quality forages that improve the nutritional status of animals which helps reduce stress of internal parasites and also can provide a situation where parasites populations are not as prolific (prepared seed bed for annual crops, taller crops that larvae can’t utilize, etc.). Other crops are considered “bioactive,” meaning they can provide a medicinal effect against parasite infestation. These crops include chicory and sericea lespedeza, which are especially helpful for sheep and goat producers.

As much as any other tool, good pasture management can help be the difference in maintaining a healthy herd free of heavy parasite loads. Coordinating with your veterinarian and Extension agent on ways you can strategically manage your herd and forages will quickly pay off.