Parasites Likely To Proliferate Due To Constant Rains

DR. TERESA L. STECKLER

SIMPSON, ILL.
   The abundant and constant rains are exactly what some pastures and crops have needed; however, with the good there seems to always be something bad. In this case, the excessive rains create conditions favorable for parasites to infect animals on pasture.
   The biggest challenge for cattle during wet weather is the brown stomach worm. Affected animals lose weight and in severe cases may die of overwhelming clinical ostertagiasis, a disease characterized by severe diarrhea, edema and serious weight loss.
   “The anthelmintic, or treatment, for this parasite can be used orally, topically or through injection,” Steckler said. “Generally, producers prefer the topical or pour-on application because they are easy to apply.” Also the pour-on application has the further advantage of providing some external control of horn flies and face flies as well as ticks.
   “Wet weather also creates prime conditions for tick infestations and ticks are a vector for anaplasmosis, which causes severe anemia and can kill livestock,” Steckler said. “And tick bites can cause swelling, redness and localized infections.”
   The recent rains are also likely to create parasitic problems for goats and sheep. Internal parasites, specifically roundworms and coccidia, can be among the most damaging problems for sheep and goats.
   Most flocks have some level of parasitic infection but may never show symptoms until optimum conditions occur. Stomach worms can actually stop their development inside the animal during adverse times and go dormant through a process called hypobiosis. When worm survival conditions improve during warm, wet weather or when the host animal’s ability to resist parasitic infection declines, such as during lambing or kidding, the worms suddenly get going again.
   The best control programs prevent parasitism prior to outbreaks. Dewormers or anthelmintics can enhance these control measures, especially when administered during hypobiosis before the eggs contaminate the pasture.
   “However, several studies indicate that parasites have become resistant to certain classes of anthelmintics due to overuse. Anthelmintics are a powerful tool, but for long term-parasite management, an integrated pest management plan should be developed for each farm,” Steckler said.
   The most damaging parasitic roundworm is the Haemonchus contortus or barber pole worm. When spring arrives, they begin to lay eggs, as many as 10,000 a day, spreading them across pastures through the animal’s manure. The eggs hatch into larvae, and with the aid of wet weather, move from the manure to plant leaves where other sheep eat them, thus completing the life cycle.
   Affected sheep or goats become anemic, lose weight, become weak and often develop “bottle jaw,” due to fluid accumulating under the jaw, Steckler said. Though various levels of loss of production are the major economical losses, death of the animal from a parasite overload is not unusual.
   “Genetic resistance in worm populations developing resistance to anthelmintics is bad; however, resistance to worms within sheep and goat populations is good,” Steckler said. “Some sheep and goat breeds are more resistant to parasites, but genetic differences can be selected for even within other breeds.”
   In general, the most susceptible to stomach worms are new mothers with lambs or kids during the first few weeks after birth, young growing animals and animals without prior parasite exposure.
   If anthelmintics are used, she advises:
   • Use the FAMACHA© system to determine which animals should be treated.  The FAMACHA© system allows small ruminant producers to make deworming decisions based on an estimate of the level of anemia in sheep and goats associated with barber pole worm (Haemonchus contortus) infection.
   • Treat only the animals that need treatment. Routinely treating all animals can lead to populations resistant to the class of dewormer being used. Leaving some parasites in the animals and on the pasture that are susceptible to the dewormer being used improves its effectiveness in later treatments. Treating only those animals that chronically need deworming also allows the manager to cull them in favor of more resistant individuals.
   • Conduct fecal egg counts to determine if the dewormer is working and what parasite is actually present. Doing so will also alert the producer that it’s time to switch classes of dewormers once a dewormer drops below an effective level or if that dewormer is effective against the parasite present. However, using multiple classes of dewormers at the same time should be avoided unless advised by a veterinarian.
   Sometimes no matter what you do, the parasite problem can get out of hand. Keep in mind that parasites cannot spread in drylots. So if you have a large problem and dewormers are not working, pen the animals until the problem is under control.
   Steckler said the bottom line is that each farm must develop its own parasite management plan, because no single program is appropriate for all operations. The plan should include a good rotational grazing management plan, smart drenching and attention to genetic selection. These protocols will differ from farm to farm based on environmental conditions, type of sheep or goat, flock/herd management and past parasite exposure. 
  While rain is almost always welcome, sometimes it can cause management headaches. Farms should have a herd health management plan to lessen the damage of parasitism in the herd. If questions still remain, it’s always best to consult your veterinarian or your Extension agent for specifics regarding anthelmintics and those management practices that will make their use the most effective. ∆
   DR. TERESA L. STECKLER: Extension Specialist, Animal Systems/Beef, Dixon Springs Agricultural Center, University of Illinois