Biting pests that might attack your horse this summer *H&H Plus*

Summer pasture is home to all manner of biting pests and parasites, as Karen Coumbe MRCVS explains...

Being outdoors at this time of year can mean battling an army of bugs and bacteria, seemingly intent on targeting the hacking or grazing horse.

Whether lurking in the long grass or flying above it, these pasture-borne pests can be more than just a nuisance – causing anything from mild discomfort to more serious ill health and even spreading disease. It pays to know the enemy and take preventative measures where possible.

The British summer produces the perfect conditions for flies, which generally benefit from a mild, wet winter, flourish around damp, woodland areas and fly in warm weather. They tend to breed in muddy, wet and unhygienic conditions, such as marshes, ditches and unkempt muck heaps.

Midges will only fly if the wind is less than four miles per hour, so a breezy hack, or a hilltop or coastal paddock would be perfect for the pony with sweet itch – a condition caused by an allergic reaction to midge bites. Other flies, including black, stable and horseflies, are also incriminated in allergic skin reactions.

In hotter, drier conditions, insects such as bees, wasps and hornets can irritate. There are stories every year of horses who have injured themselves in panic after an insect attack. Little can be done to prevent this, beyond good fencing to minimise injury risk and the sensible use of decent fly repellents, bug rugs and fly masks.

Hey, sucker

Reports suggest tick numbers may be increasing, possibly as a side effect of global warming. With climate change affecting the habitat, range and active period of tick species in the UK, along with greater international movement of domestic animals, including horses, there is increasing concern about tick-borne disease.

Ticks live in thick vegetation and attach to mammals, such as livestock, horses and dogs. They prefer areas with dense ground cover and shade, so heathland, bracken, tall grass and woodland all provide a suitable habitat. Since they avoid direct sunlight and low humidity, they thrive in springtime and a mild summer.

There are many species of tick in the UK, but Ixodes are the most numerous. Infection is more common in certain areas such as East Anglia, along the south coast and near the New Forest, so local knowledge is important. The presence of large numbers of potential hosts, particularly deer and sheep, will increase the number of ticks in an area.

Only the adult female tick sucks blood, and after a meal can measure more than 1cm in size – bigger than a coffee bean. Before feeding, ticks are smaller and harder to spot. They typically attach themselves to horses’ lower legs, heads (particularly the ears and nostrils) and areas of soft skin, including the inner thighs and under the elbows.

While infection is not thought to occur until ticks have been attached for 12 to 24 hours, they should be removed as soon as they are found. This can be difficult, however, because of their barbed mouthparts, so consult your vet rather than using a hot match, nail polish or some other home remedy. Although these methods might induce a tick to detach, they can stimulate further nasty secretions into the bite wound.

Avoid handling ticks with your bare hands, too. Any ticks found can be sent to Public Health England’s tick surveillance scheme for identification – again, ask your vet. Ticks can transmit serious disease, including Lyme disease, anaplasmosis and Louping ill in the UK, and piroplasmosis globally. Severe tick infestations can also cause skin irritations and even anaemia.

There is debate among vets and recent published research as to whether Lyme disease is overdiagnosed in horses. While blood tests reveal that many horses have been infected, very few show genuine signs of illness. So if a horse is tested and is positive with Lyme antibodies, this does not indicate that he actually has the disease – rather that he has been exposed to the infection at some stage.

Lyme disease can mimic many other illnesses and is difficult to confirm categorically, although more specific lab tests are now available. Clinical signs are vague and can include sore eyes, skin lumps, weight loss and occasionally neurological issues. The disease may be a cause of swollen joints, shifting lameness and lethargy, but there are many other explanations for such signs.

Certainly, a history of exposure to ticks increases the likelihood that Lyme disease may be present. An affected horse can be treated relatively easily with certain antibiotics but, unless the diagnosis is definitive, this may be neither beneficial nor appropriate.

Tick control includes use of insecticide repellents containing permethrin or cypermethrin, to discourage attacks and to protect the horse by irritating the tick and causing it to drop off before attachment. Products based on natural ingredients, such as botanical oils, may offer some protection for short periods.

Cutting back undergrowth and clipping or mowing pastures will make areas inhospitable for ticks and less attractive to deer and other mammals that may be carrying them.

Unseen dangers

The bacterial spores that can cause tetanus infection may be present in any soil or manure. Wherever horses graze, they have a high risk of contracting tetanus, especially if turned out in a field with additional hazards such as barbed wire. Every horse, young or old, retired or in full work, should be fully vaccinated against this frequently fatal disease.

Parasitic worms are another risk factor, but one that can be managed. An important step is to reduce the number of horses in any one paddock. Regular removal of droppings, while never a popular job, is nevertheless effective in reducing contamination of pasture by worm eggs and is far more effective than harrowing, which merely spreads the droppings around.

All the recent studies show that regular faecal worm egg counts are important in monitoring an individual horse’s worm burden. This provides a guide as to if or when treatment is needed, with the aim of minimising wormer use and reducing resistance to these important medicines.

Equine grass sickness (EGS) is a devastating condition that only affects horses with access to grass. Vets tend to see more cases at this time of year, especially among young horses and those turned out on new grazing.

The exact cause remains unknown, despite extensive research, although the condition is thought to be linked to a particular type of Clostridium bacteria picked up from the soil as horses graze. Reports suggest that risk increases with earthworks, such as holes dug for fence posts or even fresh molehills.

The disease is prevalent in certain areas, so local knowledge is useful before turning your horse out somewhere new. Supplementary feeding, with haylage on a daily basis and gradual turnout, may help, but there are no guaranteed preventative measures. Ask your vet, who will know about regional variations in EGS and other risks such as sycamore toxicity.

I have seen horses with nasty complications as a result of all sorts of incidents, from adder bites to Chinese lantern trauma. Yet despite the sometimes unusual and unpredictable hazards out there, the benefits of fresh air and exercise are many.

While there is evidence that horses come to more harm turned out in a field than they do out competing, this may be because there are more out grazing to be injured. All we can do is minimise risks – hacking with care, turning out horses in as safe an environment as possible and dealing swiftly and sensibly with any problems that occur.

Ref Horse & Hound; 28 May 2020

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