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Parasitic Diseases of Cattle

Parasitic Diseases of Cattle

Parasitic diseases impair health, reproduction, and productivity.

Parasitic diseases of cattle impair health, reproduction, growth, and productivity.  In severe cases, parasitic diseases may even cause death.  These diseases are caused by internal helminths (roundworms, tapeworms and flukes) as well as external arthropods (mites, lice, ticks, and flies).  Transmission of helminths is through oral ingestion or direct skin penetration by larval parasites on pasture.  Transmission of arthropods is through direct contact (mites and lice) or exposure to larval stages on pasture (ticks) or fly-in by adult flies or skin penetration by larval flies (grubs).

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  • Cattle in the U.S. may be exposed to nineteen genera of internal roundworms, three tapeworm genera, three fluke genera, four lice genera, four mite genera, and several fly and tick genera.  Roundworms and arthropods have direct life cycles (no intermediate host), but flukes and tapeworms have indirect life cycles (an intermediate host is required).

  • General symptoms of worm infections are rough hair coat, diarrhea, emaciation, weight loss, and/or blood loss. External parasites symptoms are hair loss (lice), scabs (mites), lumps on back (grubs), or blood loss (flies, sucking lice and ticks) and weight loss.

  • Internal roundworm parasites are diagnosed by fecal egg or larval counts from live animals. Post mortem, worms can be counted in the abomasum, intestine, lungs and liver. External parasites are diagnosed by visual observation, hair loss, or skin scrapings.

    Roundworm fecal egg counts are only reliable for approximately 4 months after exposure to a parasite species. As an animal is continuously exposed to a worm species, its worm counts and fecal egg counts rise for about 3-4 months. In most herds, there are three groups of animals:

    • A group (10-15%) of the animals which never get high worm or egg counts
    • A group (60-70%) that get moderate worm numbers and egg counts
    • A group that gets high worm numbers and high egg counts (10-15%).

    After 4 months, the egg counts drop in the second group, but their worm numbers don’t decline for another 4-6 months. In the third group, egg counts don’t decline for an additional 4-6 months, and the worm counts decline another 4 months later.

    One genus, Ostertagia, is never adequately controlled by the immune system and may continue to produce eggs after the time frames above.

    Egg counts are unreliable because of these two patterns.

    In addition we are unable to count immature worms.

    Bottom line, predicting worm burdens, assessing efficacy, or basing a treatment on egg counts is not a reliable practice.

    Cattle liver fluke or stomach fluke diagnosis can be done by fecal egg counts or post mortem examination of the liver or abomasum.

    Deer flukes do not enter the bile ducts, therefore there are no eggs in the feces. They can only be diagnosed post mortem by liver examination.

  • Best practices include cattle being treated at the beginning of a roundworm/fly or lice infection period with a long acting product to eliminate existing roundworm or arthropod parasites and prevent reinfection if the animals are in an environment where there is infection challenge.

    Cattle are treated in fall to prevent lice infestations and to clean up summer worm infections in Northern states with an endectocide or a combination of an internal and external parasiticide.

    Cattle are treated for liver flukes with a product labeled for flukes when animals are heavily infected or two months after the snails (intermediate host) have gone into estivation (dormancy). This is: September in the Southeast or February in Northwest.

    Cattle raised in confinement should be treated to clean up existing mite/lice infections or before adding new animals to the existing herd with an endectocide or external parasiticide.

  • For internal parasites, raise cattle on dry lots or cultivated crops. For lice or mites, quarantine new animals and treat for infection before mixing with herd.  For cattle grazing on permanent pasture, treat with an endectocide  at the beginning of the grazing season.  Graze worm-free calves on larval-free pastures before grazing cows.

  • Data indicates that heavy horn fly infections of cattle (100 flies in North or 200 flies/animal in South) reduce gain by 0.1 lb/day while heavy sucking lice infections reduce gain by 0.1 lb/day.

    Data from fluke-free cattle demonstrate that they gain an additional 0.2 lb/day in feedlot compared to cattle that have been infected by flukes (treated or untreated at entry).

    Data indicate that grazing calves or stockers or feeders infected with internal roundworms on permanent pastures or in feedlots reduce gain by 0.1 to 0.5 lb/day depending upon the severity of infections, feed availability and the immune status of the animals.



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