Worm and Dag Management for Sheep

In areas where dags and scouring occur they can be a greater flystrike risk than wrinkles.

As dag score increases, the risk of breech strike increases dramatically. A Dag Score 2 sheep is twice as likely to be struck on the breech as a Score 1 sheep. A sheep with Dag Score 4 is seven times more likely to be struck than a Score 1 sheep. The causes of scouring can differ in summer and winter rainfall areas.

Summer rainfall environments

In summer rainfall areas the major causes of scouring and dags are

• worm or larval challenge in sheep with little immunity
• rapid change to a high quality pasture
• occasionally coccidia

Winter rainfall environments

In winter rainfall environments the major causes of scouring and dags are

• heavy worm burdens or larval challenge in sheep with little immunity
• larval hypersensitivity in worm immune sheep

Worm egg counts

A worm egg count (WEC) is essential to determine the cause of the scouring and whether drenching or some other management response is required. To do a worm egg count—push the sheep to an area where they will stand for 10 minutes. Let the sheep walk away after 10 minutes and collect 10-15 faeces samples in separate plastic bags. Keep the samples cool (do not refrigerate) and send to your vet or local testing centre in an esky as soon as possible.

Scouring in sheep with little immunity

Lambs between 4 and 8 months of age may not have developed adequate immunity to worms. In particular, late born lambs in winter rainfall environments, may not get adequate exposure to green pasture in the first winter to develop immunity. As hoggets in the following winter these animals may suffer from scouring. Drenching will remove the worm burden and scouring will cease. The animals will develop immunity with time. Lactating ewes can suffer a temporary loss of immunity to worms and this may result in scouring for a short period of time.

Larval hypersensitivity scouring

Larval hypersensitivity scouring can occur in sheep that are immune to worms, but experience a reduction in their immunity over the long hot summer, when no worm larvae can survive on the pasture. During the subsequent winter, sheep exposed to large numbers of larvae may suffer a massive immune response, which causes inflammation of the gut and scouring. The sheep do not usually suffer ill-health or weight loss and will recover as immunity re-develops. If the number of affected sheep in the mob is small it is possible to cull the affected animals.

Managing dags, scouring and flystrike risk

Effective management of dags and scouring is essential for reducing flystrike risk. Understanding the cause and appropriate treatment for any scouring is the first step in reducing that risk.

• Use worm egg counts to monitor worm burdens and understand the causes of scouring in the flock.
• Use WormBoss to develop an effective worm management strategy and drench program.
• Use crutching strategically to remove dags during high risk periods for flystrike.
• Consider selecting rams that have low Worm Egg Count (WEC) and Dag Score (LDAG) ASBVs and low Dag Scores.