DULUTH, Ga. — Not only do external parasites turn a shiny coat into a tattered one, they also can reduce the comfort, efficiency and overall performance of your dairy herd.
“If you’ve ever had a case of poison ivy, you likely were uncomfortable and didn’t get your best night of sleep,” said Stephen Foulke, DVM, DABVP, Boehringer Ingelheim. “This is comparable to cows distracted by external parasites — instead of resting and producing milk, they’ll spend their time itching, scratching or bunching into groups.”
The following external parasites commonly affect dairy cattle comfort:
1) Mange mites attack and damage the skin and hair. Chorioptic mange (C. bovis) can cause hair loss, scabbiness and dermatitis around the feet, legs and tailhead. Mange-infested skin typically swells and can become inflamed. Sarcoptic mange (S. scabiei), a quarantinable mite, causes even more-severe skin lesions than C. bovis — infection by just a small number of these mites can be detrimental to an animal’s health and production.
2) Biting flies are one of the costliest external parasites for producers. The sheer number of flies typically found in a herd renders them a constant threat.
The economic threshold for horn fly presence on cattle is 100 or more per lactating dairy cow, and stable fly threshold is often accepted as five flies per animal leg. If fly densities reach or exceed the economic thresholds, treatment will provide a return on investment through improved cattle health and production.1
Alec Gerry, PhD, a professor of entomology at University of California Riverside, says that biting flies feed on the blood of cattle and cause very painful bites. “There are some discrepancies on the exact economic threshold numbers for biting flies, but it’s clear that high numbers of these flies in your herd will negatively impact production efficiencies in terms of weight gain and milk production,” he explained.
3) Lice are also known to reduce weight gain and decrease general thriftiness of dairy cattle. Typically found in colonies on the tail, shoulders and back, biting lice feed on cattle by scraping the skin or hair. Sucking lice, such as the short-nosed, long-nosed and little blue lice, extract the blood of their host.
4) Cattle grub can cause poor weight gain and losses in milk production. Cattle defend themselves from the grubs’ irritation by actively running away or spending excessive time in water, hindering proper grazing or relaxing. Grubs can migrate into their host’s esophagus and negatively affect the health of the animal, as well as cause damage to meat, which may require discard at slaughter. These parasites are best controlled with macrocyclic lactone dewormers, and timing of the dewormer application is critical.2
The importance of parasite identification and monitoring
In today’s competitive market, not treating your herd for external parasites isn’t worth the risk. Knowing exactly what types of parasites are impacting your herd is the first step in selecting deworming products and administering those products at the right time.
“Producers dealing with cattle grub, for instance, should consider when the grubs are moving through the body,” said Dr. Gerry. A deworming treatment for cattle grub should be applied in the fall, when the grubs are too small to cause issues because they die within the animal. If the dewormer is applied in the late winter months, the grubs are larger, and their death may result in an internal infection within the host animal.
On the flip side, parasites like lice and mange are usually a problem in the winter months because cooler temperatures and longer hair coats favor these parasites’ survival. Deworming too early in the fall will not knock down a lice population because it’s likely not even there yet.
“Diagnostic tests are the most accurate way to determine the most prevalent parasites in your herd, but parasite monitoring can also be as simple as asking your veterinarian if they notice any lice or tailhead mange during preg-checking,” noted Dr. Foulke.
With properly timed deworming applications, parasite monitoring, veterinarian consultation and the use of a proven product, producers can keep parasite populations at bay to ensure cows are happy, healthy and productive.
1 Kaufman PE, Weeks EN. Horn fly management. University of Florida Extension. 2013. Available at: https://edis.ifas.ufl.edu/pdf/
2 Veterinary Entomology (a pest management and education resource). Cattle grub. Available at: https://www.
–Boehringer Ingelheim Animal Health USA Inc.
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