Worms can be a significant problem with dairy-bred calves if they are not managed correctly.

In a suckler to weanling system, the calves are generally not exposed to the same level of lungworms and gutworms, as cows have a naturally acquired immunity and hoover up a large proportion of the infective larvae on the grass.

For that reason, a correct dosing plan to suit the farm, combined with good grassland management, is essential to reduce worm exposure.

Gutworm

Gut worms are most common in calves during the summer months, from June to September. Once ingested, they affect the animal’s stomach and intestines and cause gastroenteritis.

Symptoms include calves having prominent watery, green diarrhoea. Animals can also suffer a loss of appetite and a rapid weightloss of 10% to 20% within a 10 to 14-day period.

Lungworm

Lungworm (hoose) is generally more of an issue from mid- to late-summer onwards, but the recent warm, humid weather following rainfall creates ideal conditions. A husky cough with an extended tongue is the most common symptom.

The total lungworm cycle takes 28 days, from ingestion as larvae on grass, until they are passed out in faeces onto grass again.

After approximately one week on grass, the larvae are infectious again.

There are a few steps to take to reduce the exposure levels to calves:

  • Graze paddocks in rotation.
  • Use a leader/follower system where available.
  • Utilise silage aftermath for calves where possible.
  • Dosing programme

    There are several different products containing various active ingredients, which will control lungworms and gutworms. Depending on the active ingredient, the length of control will vary.

    Avermectins/milbemycins come in the form of injectables or pour-ons and have a persistency period ranging from 21 to 35 days. They are the more expensive option, but do provide a greater period of cover to the calf.

    Levamisoles are golden or clear drenches while benzimidazoles are white drenches. These are inexpensive but have a shorter persistency period and by using them it means more frequent dosing will be required.

    It is essential that, when creating the correct dosing programme for your farm, you consult your vet. Varying between active ingredients from one year to the next may help to reduce the risk of resistance occurring.

    To avoid the build-up of resistance to larvae on pasture, return calves to the paddocks they were in after dosing for another two to three days, before moving to fresh pasture.

    Building immunity

    The objective of dosing should not be purely to kill all worms. Treating too early means there will not be an effective kill and shorter residual cover period. Treat too late and animal performance has already been affected.

    Calves should be allowed to build immunity through exposure to worms for a short period of two to three weeks between doses.

    For example, ivermectin has a persistency of approximately 21 days. To help build immunity, the next dose should not be administered for approximately five weeks after the first so that the animal can build natural immunity to the worms.

    DO

  • Create a dosing plan with your vet.
  • Take faecal egg counts.
  • Implement a dosing plan to build immunity.
  • DON’T

  • Only dose when calves are coughing.
  • Set stock fields for long periods.
  • Keep calves on dirty pasture for 48 hours post-dosing.
  • Use a dose with the same active ingredient year-on-year.
  • Read more

    When and why should you feed meal to calves at grass?

    Managing dairy-to-beef calves at grass

    How to successfully wean a dairy calf