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Stop parasites, improve dairy

Stop parasites, improve dairy

External parasites can reduce the comfort, efficiency and overall performance of dairy cattle. Instead of resting and producing milk, they’ll spend their time scratching or bunching into groups, says Dr. Stephen Foulke, a veterinarian at Boehringer Ingelheim. There are  several parasites that commonly affect cow comfort.

Mange mites attack and damage cattle skin and hair. Chorioptic mange can cause hair loss, scabbiness and dermatitis around the feet, legs and tailhead. Mange-infested skin typically swells and can become inflamed. Sarcoptic mange, a quarantinable mite, causes even more severe skin lesions. Infestation by just a small number of such mites can be detrimental to an animal’s health and production.

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. 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.

Biting flies feed on the blood of cattle and cause painful bites.

“There are some discrepancies on the exact economic threshold numbers for biting flies, but it’s clear that great numbers of the flies in one’s herd will negatively affect production efficiencies in terms of weight gain and milk production,” said Alec Gerry, a professor of entomology at the University of California-Riverside.

Lice are 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.

Cattle grubs can cause poor weight gain and losses in milk production. Cattle defend themselves from grub irritation by actively running away or spending excessive time in water. That hinders grazing or relaxing. Grubs can migrate into their host’s esophagus and negatively affect the health of the animal. That also can cause damage to meat, which may result in discarding at slaughter. Such parasites are best controlled with macrocyclic lactone dewormers. Timing of the dewormer application is critical.

Learn parasite identification

In a competitive market, not treating one’s herd for external parasites isn’t worth the risk. Knowing exactly what types of parasites are affecting the herd is the first step in selecting dewormers and administering those products at the correct time.

“Producers dealing with cattle grub, for instance, should consider when the grubs are moving through the body,” Gerry said.

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. Their death may result in an internal infection within the host animal.

On the flip side, parasites such as lice and mange are usually a problem in the winter months because cooler temperatures and longer hair coats favor parasite survival. Deworming too early in the fall won’t manage 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 also can be as simple as asking a veterinarian if they notice any lice or tailhead mange during preg-checking,” Foulke said.

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. Visit for more information.

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