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Monitor Worm Control Effectiveness

The effectiveness of worm control programs should be monitored to ensure that worm burdens do not reach significant levels. Changes in seasonal conditions, or to cattle management, can allow larger numbers than expected to build up – even when animals have been drenched as part of an annual program. Moderate worm burdens may cause some production loss without any obvious signs of worms being present (‘sub-clinical loss’).

In higher rainfall and temperate environments, some on-going loss of production due to worms is common in younger age classes, so monitoring for signs of worms is important, and a planned program may be necessary. Worm egg counts provide a reliable estimate of worm burden in animals under 18 months.

Even in environments where worms only occasionally cause significant production losses, worm problems may develop gradually over time, and it is important to be aware of the seasonal conditions where more frequent monitoring of animal performance is wise.

Checking for the presence and effects of harmful worms involves:

  • Monitoring the growth rates or body condition of calves and yearling cattle, to check that they are as expected for the nutrition available. Reductions in weight gain often continue over long periods without progressing towards more severe signs of worm disease. This differs from the situation in sheep and goats, where worm burdens tend to increase rapidly, and the typical signs become obvious.
  • Checking the worm egg counts of affected mobs is the first step towards establishing the cause, particularly where more obvious signs of worms are present. Most of signs of large worm burdens are not specific for worms (such as scouring, rapid weight or condition loss, sometimes a harsh and dry hair coat, and if barber’s pole worm; Haemonchus placei is present, anaemia), and may in fact be due to various infectious diseases, mineral deficiencies and other causes.
  • Checking worm egg counts of affected mobs usually indicates the size of worm burdens, and hence whether these are the likely cause. However, the interpretation of worm egg counts in cattle is less straightforward than in sheep or goats. Unless counts are very high and a diagnosis of worm disease is obvious, it is recommended that a veterinarian or animal health adviser is consulted.

Drenching worm-affected cattle should result in an immediate improvement and confirms that worms were involved.

However, worms may not be your sole problem as under-nutrition may predispose cattle to outbreaks of worm disease. In the absence of a clear response to treatment, you should seek further advice, and worm egg counts will almost always be the first step towards a diagnosis.

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