Procedures for Sheep Research Facility Parasite Management

Unit for Laboratory Animal Medicine
Apr 5, 2024 12:00 am

To describe the methods of management and screening for internal parasites in University of Michigan sheep housed at the Sheep Research Facility (SRF).

  • Responsibility

    1. Sheep Research Facility Shepherd: Responsible for collection of parasite screening fecal samples and daily monitoring for signs of animal parasitism.
    2. ULAM Veterinary Personnel: Responsible for submission of fecal samples and the prescription of antiparasiticides as needed.
  • Glossary Definitions


    A pharmaceutical used to destroy and eliminate intestinal parasites.

    Anthelmintic Resistance

    A term used to describe an intestinal parasite which is not 90% cleared following treatment with a specific anthelmintic.


    A visual system using the color of the conjunctiva of sheep to assess the need for deworming, via the severity of anemia, to aid in prevention of anthelmintic resistance.

    McMaster Test

    A diagnostic method to provide quantification of intestinal parasite eggs in feces, reported as eggs per gram (EPG).

  • Procedures

    1. Selection of Anthelmintics

    1. Three classes of anthelmintics, represented by albendazole, ivermectin, and levamisol will be utilized.
    2. Veterinary personnel will determine the anthelmintic of choice given the season and animal/flock history. Routine annual rotation of anthelmintics may be considered for long-term, pastured flocks.
    3. Moxidectin, or combination anthelmintic treatment, will be used to treat resistant populations of parasites and its use will be reserved for treatment of sheep with resistant parasites.

    2. Prophylactic Anthelmintics

    1. New arrivals
      1. Sheep vendors are required to deworm animals at least 5 days before delivery to the Sheep Research Facility. No other prophylactic anthelmintic therapy will be provided to new arrivals.
    2. Employment of the following prophylactic regimens will be at the discretion of the veterinarian.
      1. Breeding/Lambing/Weaning
        1. Breeding ewes and rams will be dewormed 2 weeks prior to breeding.
        2. Pregnant ewes will be dewormed 2 weeks prior to lambing season. If lambing season is greater than one month, late lambing ewes may receive a second deworming prior to lambing.
        3. Lambs will be dewormed at the time of weaning.
      2. Pasture animals (adults only)
        1. All pasture animals will be dewormed once in the winter months (November-April) and once between April and November. This deworming is in addition to the breeding-related deworming previously described.
      3. Dry lot animals
        1. Dry lot animals may be dewormed once in the late fall/early winter.

    3. Fecal Examinations

    1. New arrivals – A fecal is collected 10-14 days after arrival to assess efficacy of the vendor anthelmintic treatment.
    2. Resident flock – Monthly examinations will be performed on feces randomly collected from 20% of the flock population and/or individual animals per veterinary guidance.
      1. These samples may be pooled together at the discretion of the veterinarian.
      2. If sample collection corresponds with a scheduled prophylactic deworming, the fecal samples must be collected prior to the deworming.
    3. Fecal samples will be submitted to ULAM Pathology Core for processing.
      1. ULAM veterinary personnel are responsible for filing copies and interpretation of fecal examination results within the medical records.
    4. The McMaster test will be utilized for quantification of parasite burden. Veterinary discretion will be used to determine if treatment is needed on a case-by-case basis.
      1. Generally, nematodes >1000 EPG will be used to indicate additional clinical assessment is needed.
        1. Clinical assessment of the individual animal and/or herd will utilize the FAMACHA system to assess the severity of anemia. Housing environment and additional clinical signs of parasitism will be used to determine when anthelmintic treatment is necessary.
          1. FAMACHA score of 3 or above indicates the need for anthelmintic treatment.
      2. If treatment is prescribed, a follow-up McMaster test will be completed 10-14 days post-anthelmintic treatment. Less than a 90% reduction in parasite load following anthelmintic treatment will be deemed as resistance.
        1. Moxidectin, or combination anthelmintic treatment, will be administered to animals in need of deworming with resistant parasites.

    4. Coccidiosis

    1. Coccidiosis will be diagnosed in sheep having >2000 coccidia per gram of feces with the presence of diarrhea.
    2. Options for coccidiosis treatment include sulfonamide, sulfaquinoxaline, or amprolium for a period of five days.
    3. A coccidiostat, such as monensin, lasalocid, or decoquinate, may be used regularly to reduce coccidia contamination of the environment.
      1. For pregnant ewes, the coccidiostat should be added to the diet at least 21 days prior to lambing to benefit the lambs.
  • References

    1. Maryland's Small Ruminant Page
      2. Medicine Cabinet for Sheep and Goat Producers
      3. Coccidiosis in lambs - Michigan State University
    2. University of Nebraska-Lincoln
      2. Cooperative Extension
    3. Government of Alberta
      1. (Dr. Des Hennessy, CSIRO Animal Production Center)
Species: Sheep

Questions or concerns about the content of this document should be directed to the Unit for Laboratory Animal Medicine (ULAM) at (734) 764-0277 or