Thiabendazole is effective and very safe. It is given orally and can be used in lactating cows if milk withholding times are observed. Whenever drugs are used, observe label directions for proper use and observe meat and milk withholding times as well as label precautions. Consult a veterinarian for diagnosis and information on treatment of parasitism. None of the wormers currently available and labeled for use in cattle eliminate arrested larvae of Ostertagia.
Some new anthelmintics being developed are effective against arrested larvae.
When they are permitted for use in cattle they will provide an advantage over current products. Cattle that continue to graze infective pastures or cattle harboring large populations of larvae in their abomasal glands will develop adult worm burdens following treatment. Treatment itself does not preclude re-infection. As of this writing, more than 20 trials have been conducted to determine the importance of worming adult dairy cows. Early work indicated that worming cows at calving time would result in a positive production response.