Recent hot weather saw an explosion in fly numbers

HERD HEALTH SERIES: Maura Langan, Commercial and Technical Manager (Large Animal) at Norbrook.

Warmer weather allows for faster lifecycles, meaning that fly numbers can increase rapidly with just a few days above 20 °C. Other environmental factors include humidity, standing water, decaying vegetation and faecal matter, so it’s no surprise that Irish farms can face significant problems anytime between April and November.

Flies cause more than just irritation. There are at least 20 common species of flies which feed on the blood, sweat, skin secretions, tears, saliva, urine or faeces of cattle. Biting flies puncture the skin directly, and non-biting or nuisance flies scavenge at the skin surface, wounds or body orifices.

Cattle react to fly activity by movement into shade, restlessness, skin rippling, or simply stamping and tail switching. In extreme cases,s cattle may be so distressed that they damage themselves through rubbing, kicking or other escape behaviours.

All these activities result in cattle using more energy and spending less time grazing and lying. Reduced feed intake and the irritation and stress caused by the nuisance and painful bites of flies hurt the productivity of dairy cows, with reduced milk yields of up to 20% observed.

The fly activity also spreads disease. Face flies and the stable fly act as vectors transmitting the bacterial causes of infectious bovine keratoconjunctivitis or ‘pink eye’. This can cause severe ocular damage and requires antibiotic treatment. There is also a knock-on, long-term effect on productivity; affected cattle can suffer a significant reduction in weight gain when compared with healthy cattle.

Dry cows and heifers are also at risk of developing Summer Mastitis caused by bacteria transmitted by head flies. This painful and damaging infection requires urgent veterinary intervention, and the affected quarter rarely recovers. The cost of antibiotic treatment and a drop in overall future milk production can have a significant impact.

While a certain number of flies can be expected, farmers can make some changes to reduce their impact. Low-lying, still areas with standing water, long grass and trees or hedges are a haven for flies. Avoid grazing these areas at periods of peak risk and move cattle regularly to reduce the faecal matter on the pasture.

The hot, moist conditions of a milking parlour are also attractive to flies, so consider fly traps, insect killing lights, and fly killing paints. Improving ventilation with the installation of fans may help. Hygiene is essential as flies lay their eggs in rotting vegetation and faeces. Consider management of manure heaps, including spreading them or relocating them, as they are often the source of flies on the farm.

The use of spot-on products for cattle is an effective way to reduce the impact of flies on livestock. Regular use, starting early in the season, can help to reduce the overall number of flies affecting your herd. All cattle in the management group should be treated.

Spotinor Spot-on Solution for Cattle and Sheep contains 10mg/ml deltamethrin, a pyrethroid insecticide known for its speed of action and potent kill. It is a convenient and effective option to control a range of flies, lice and other external parasites that affect livestock throughout the year. It has an easy spot-on application, and the simple 10ml dose for cattle means no need to weigh animals before treatment.

Farmers should continue to treat at regular intervals throughout the season to prevent a build-up of flies. Your vet will be able to advise a suitable regime that is specific to the needs of your farm.

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