July 16, 2021

SSASAS: SCC 81 Symposium

SSASAS: SCC 81 Symposium

Dr. Christine B. Navarre presented the first talk about “Best Management Practices for Parasite Control in Beef Herds in the Southeastern United States”.

According to her, due to anthelmintic resistance in common gastrointestinal nematodes (GIN) of beef cattle, a new approach to parasite control in beef herds is needed. Recently, it has been difficult to create a parasite control program as the ability of cattle dewormers has been worsening overtime. Since there are no new products in development, a new way of managing parasites is needed to slow down resistance. Anthelmintic resistance is reduction of efficacy of a dewormer. A parasite control program needs to be sustainable for the long term. Parasites can cause decreased weight gains, decreased reproductive efficiency and milk production, impaired immune system, and decreased appetite in young cattle. Impacts of parasites on the ranch are unpredictable and vary from year to year. Weather, temperature, moisture, rain impact parasite numbers on pasture. Larvae die out more quickly in summer so the pasture can be cleaned up if left ungrazed, but rain is necessary so larvae come out and die. Pasture rotation time depends on pasture type, quality, and drainage. It is difficult to predict the level of parasites as research does not give an idea of individual operations. Breed, genetic susceptibility, other stressors, adequate nutrition, previous exposure, and level of dewormer resistance impact the number of parasites in an animal. Overall, eliminating all parasites is not sustainable. Instead, it is important to dilute resistant worms in the population. Refugia can be used to slow drug resistance. Some refugia can be maintained by not treating all animals in the herd. Good worms can be left to be bred to bad worms to slow resistance. It is necessary to find out when it is actually appropriate to deworm. Fecal egg counts can best be used to determine when not to treat animals with dewormer since times of low risk for worm challenges is a high risk for resistance if the animals are treated. Refugia-based strategies such as targeted selective treatment and selected non-treatment can be used to control parasites. For example, using replacement heifers, 10% to 30% can be left untreated with dewormer, the 10% that are the heaviest can be left untreated, or every 10th animal can be left out of treatment, but there are always exceptions. In deworming for liver flukes which are particularly deadly, 10% to 30% should still be left untreated and then should be monitored. In using dewormers, it is important to always use a combination of classes of dewormer with a refugia program and dose cattle with the dose for the heaviest cow to avoid underestimation. In general, deworming in feed/minerals should be avoided because the doss cannot be controlled. Overall, parasite control requires a balance between short term economics and long term sustainability that can begin with managing pastures for grass health and cattle nutrition. 

Joan M. Burke, PhD presented next about “Multi-species Grazing for Control of Gastrointestinal Nematodes – a Review”.

In the southeastern U.S. environment, one of greatest health challenges in small ruminant production is control of GIN. According to Dr. Burke, in small ruminants, anthelmintic resistance is more prevalent than it is in cattle. Anthelmintic resistance is widespread in small ruminants and involves all drug classes. It is inevitable and permanent, but can be slowed by treating individuals rather than herds. This involves a multifaceted approach that includes multi-species grazing. Parasites can be controlled by determining the parasites present, when they are being transmitted, how they survive, anthelmintic effectiveness and appropriate administration time, or use of other control methods. Alternate grazing of cattle with small ruminants can benefit GIN control because GIN species differ between host animals. A multifaceted approach to GIN control is recommended for farmers with alternate grazing being the most common due to management differences in small ruminants and cattle. Susceptibility to GIN depends on age with younger animals typically being more susceptible. Multi-species grazing slows down pasture accumulation of larvae that affects both species. Challenges to multi-species grazing include different mineral requirements between species, predators that small ruminants are more prone to, different working facilities, fencing, and challenges to design research studies. There are several multi-species grazing strategies including grazing together, grazing in alternate seasons every 2 to 6 months, and leader-follower which involves rotating months of grazing separately. A 50:50 grazing ratio of cattle to small ruminants is suggested. Production phase and species must be considered for multi-species grazing. Additionally breeds with disease or GIN resistance and tannin rich forages can be considered for parasite management. Multi-species grazing is not always consistent in lowering worm burden as body weight is often improved in small ruminants but not in cattle. Rainfall, drought, animal stressors, stocking rate, forage type and quality can contribute to success or failure of multi-species grazing. Multi-species grazing can also be used along with other methods of GIN control. 

James E. Miller, a veterinary parasitologist, concluded the symposium with a presentation on “BioWorma as an Aid for Controlling Ruminant Nematode Parasites”.

According to him, in the use of modern broad spectrum anthelmintics, control emphasized treating all of the animals in the population and concentrating treatments to the time of year when infection was high. Classes of dewormers have different modes of action. According to Miller, it was thought that there would be adequate control for years to come and that classes of dewormers would continue to be developed. Widespread resistance to dewormers was observed in the 1990s and 2000s. Today, resistance to several classes of dewormers is common on many farms. Factors that affect development of resistance include deworming all animals in population, deworming more than necessary, deworming at times of low environmental refugia, and under dosing. Dewormers failed as resistant populations became more predominant. Unsustainable control has been attributed to sole and frequent use of dewormers. There are several non-drug alternatives such as copper oxide wire particles but sheep are susceptible to copper toxicity and there is no scientific evidence that alternatives such as herbal dewormers are effective. To manage dewormer resistance, it is important to consider sustainability and accept some reduced productivity. Nematode-trapping fungi such as Duddingtonia flagrans spores (BioWorma) can be used to trap larval stages of gastrointestinal nematodes in the fecal environment. BioWorma can be mixed into supplement feedstuffs daily to allow for control of gastrointestinal nematodes in livestock. It needs to be fed for a period of at least 60 days beginning at the start of the grazing season to optimally control larvae. BioWorma can also be mixed into loose mineral supplements as long as it is covered and dry. Since BioWorma is expensive, research is evaluating other delivery methods that would be cost effective, but BioWorma is currently the only method to target resistant nematodes on pasture.