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Counting Fly Numbers on Cattle

Threshold buffalo fly numbers for treatment

  • Beef cattle: flies exceed 200 per animal
  • Dairy cattle: 30 flies per cow

Monitoring buffalo fly numbers on cattle is important in making appropriate management decisions. Routine monitoring will help to determine when to treat and to evaluate the efficacy of current or new controls. It can provide early warning of the emergence of insecticide resistance or problems with other control methods and will aid the identification of particularly susceptible animals in a herd.

The normal recommended threshold for treatment of buffalo flies is when average fly numbers for beef cattle exceed 200 per animal or when some cattle in the herd are starting to show significant irritation from the effects of flies. For dairy cattle the treatment threshold is lower at about 30 flies per cow.

Whole body counts are the most accurate but in practice are difficult to make. Counting the number of flies on one side of an animal and then multiplying by 2 is usually the most practical option. Using binoculars can help increase the ease and accuracy of field counts. However, beware that flies may not be evenly distributed and can be concentrated on one side of the animal under the effects of sunlight and high temperatures, or following disturbance of the flies by the observer during counting.

Counts should be made on at least 10 animals to produce the average count. When average counts approach the economic threshold, or some animals in the herd are starting to show significant irritation from the effects of the flies, treatment or initiation of other control methods should be considered.

Fly counts are best made early in the morning as most of the flies will be obvious at that time, later in the day as the sun becomes stronger more of the flies will be resting on more shaded parts of cattle such as on the belly, underside of the neck and dewlap and will be difficult to see. Early in the season when fly numbers are low it may be possible to count individual flies. However, as fly numbers get higher the best method may be to estimate numbers by counting groups of flies, for example groups of 5 flies or even groups of 25 when fly numbers are close to the threshold.

Another possible method is to use a camera to record fly numbers, or sometimes even a good quality mobile phone camera when the cattle are quiet and can be approached closely. If good photographs can be achieved, the number of flies can then be counted later, back in the house or office by downloading to a computer and magnifying images on a computer screen. If this method is used it is generally a good idea to photograph more than 10 animals as some photographs will inevitably be out of focus and not useful. This method can be quicker and more accurate but takes some practice to get right.

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