Mites in horses

Mites are all around us. These eight-legged arachnids live in our homes, our horses' stables, and even (in the case of some species) on, or in, equine skin. They feed on skin flakes and secretions and cause severe itching. These tiny parasites are not only annoying, they can also be dangerous for your horse. Learn here about the consequences of mite infestations for your horse and what you can do to fight them.

What are mites?

Mites are arachnids. They are found all over the world in various forms and in all kinds of environments. The most well-known variety, as well as the largest, is the tick. Other species are only visible under a microscope. Common to all mites are their developmental stages: from egg to six-legged larva, through the nymph stage to the adult eight-legged mite.

There are about 30,000 known species of mites: around half of these live in soil and feed on plant tissue. Other species are adapted to certain environments. Only a few are parasites, dependent on the skin or blood of other animal species. These colonise their host animals and can remain active and multiply throughout the year due to the body heat produced by their host. Some mites live on human skin and are constant, undetected guests on our horses. Whether this is creates problems for the horse will depend on the number of mites and the horse's constitution. Weaker horses are especially susceptible to mite infestations. For example, skin problems caused by mites were among the most common diseases among cavalry horses in the First World War, affecting 67% of all horses. 

Parasitic mites that live on or in animal skin often have powerful mouths for biting and their increased presence can not only bother their host, but also cause serious problems. The symptom complex caused by mites is known as mange. When mites appear in great numbers, they weaken the afflicted horse through skin inflammations and chronic lesions which attract bacterial secondary infections.

Mites like warm, moist environments and especially prefer dark places. They multiply rapidly: shortly after fertilisation, the female lays up to 100 eggs which hatch within a few weeks. Infection occurs through direct contact or through infested grooming items or tack, rugs, etc. The parasites can also be picked up from scratching posts and brought into the stables.

What are the signs of mite infestations in horses?

The main symptom of a mite infestation is severe itching. The horse is restless, gnaws at the afflicted areas, rubs against objects and stamps its hooves in attempts to relieve the itching. The horse's insatiable urge to scratch makes one first think of sweet itch. Horses can scratch and gnaw themselves to the point of self-mutilation. Intense scratching leads to hair loss, lesions, chronic changes in the skin, and secondary infections caused by germs.

If your vet suspects that your horse has mites, a skin scraping will be done. Small skin samples are scraped off the affected areas. These are then examined under a microscope to identify the exact species and determine treatment. 

Which mites infest horses?

Horses most often fall prey to Chorioptic or feather mites (Chorioptes equi). These are mites which live on the surface of the horse's skin and feed on dander and skin secretions. They can live for up to ten weeks without a host and are difficult to eliminate from the horse's environment. Peak season for Chorioptes mites is in autumn and winter, when horses spend more time in the stable. They thrive in moist, warm environments, muddy paddocks, and from conditions involving poor hygiene or stress. However, turned out horses can also contract them from damp pasture grasses. Softened from constant moisture, the weakened skin becomes a breeding ground for the pests.

Chorioptic mange leads to leg mange, which mostly occurs at the back of the pastern and spreads upwards over the cannon bone towards the trunk. Horses with a long feathering, such as draught horses or Gypsy Cobs, are particularly susceptible, but no breed is immune to these mites!

The following symptoms are signs of an infestation of Chorioptic mange mites. The skin on the back of the pastern becomes red and covered with grey, grainy scales. The affected areas will typically feel like nubs at first. The scales and nodules develop into an oozing, greasy or crusted, scabby eczema. Long, dead patches of skin come off along with hair during grooming. Afflicted horses suffer from severe itching and make attempts – sometimes with acrobatic contortions – to bite at their pasterns, stamp their hooves violently, or even kick walls. The irritated skin can become inflamed and swollen from bacterial secondary infections. If the germs penetrate to the subcutaneous tissue, they cause phlegmons. Left untreated, significant skin formations can develop, subsequently leading to chronic skin conditions like greasy heels.

Chorioptic mange mites can also be found on symptom-free horses. These animals are "silent carriers" and contribute to the mites' spread.

Itch mites (Genus Sarcoptes equi) burrow 1 cm deep into the horse's skin, where they feed on skin cells and tissue secretions and cause severe itching. The highly infectious Sarcoptes mange begins at the horse's head. Because the itch mite needs thinly haired areas of the body in order to penetrate the skin, it prefers to colonise the neck, shoulder, and saddle area of sleek summer coats. Nodules and blisters first appear on the head and withers. This leads to hair loss, scabs and crust formations which spread over time to the back and flanks. The skin becomes coarse, wrinkled, and covered with grey-white scaly deposits. The other limbs are not affected. The horse becomes severely weakened from the large lesions and constant itching. Sarcoptic mange can even be fatal for the horse.
Humans can also contract Sarcoptes scabiei, known as the itchy condition pseudoscabies. Because humans are not viable hosts for Sarcoptes scabiei, these symptoms disappear on their own after two or three weeks. Nevertheless, some countries, including Austria, require that cases of sarcoptic mange be reported to the relevant authorities. 

Psoroptic mange in horses is caused by mites of the genus Psoroptes equi. Psoroptes mites live on the skin and cause crusting. The mites dwell under and between these crusts, feeding on blood and tissue fluids. The parasites bite deeper layers of the skin to reach food. In horses, they mainly colonise thick hairs, such as mane and tail hair, as well as other thickly haired parts of the body. They spread from the forelock and mane over the body down to the hocks. They can also be found on the penis and udder. Symptoms range from hair loss, crust formations and skin thickening to bacterial secondary infections. 

Unlike itch mites, Psoroptes mites spread slowly. Infested areas are recognised easily, as they become dry and papery. Psoroptic mange in horses is rare.

Ear mites (Psoroptes cuniculi) settle in the outer ear and the external ear canal. In severe infestations, ear mange can also spread to other areas of the head and body. A characteristic sign is skin of the outer ear that is dry, flaky and sensitive to touch. Other symptoms of ear mange include severe shaking or tilting of the head and rubbing the ears against objects.

Autumn chiggers (Neotrombicula autumnalis), or more specifically their larvae, are contracted by horses at pasture and burrow into areas with thin skin to feed on skin cells. They can be seen as tiny red dots on the horse's skin. However, these fall away after a short time and continue their development in the soil. This mite species is particularly active in late summer and autumn and causes trombiculosis, which can also affect humans and dogs ("chigger bites"). Infestation in horses causes small oozing, itchy wounds on the back of the pastern and the coronary band, often also on the nostrils, the inside of the legs, udder, and penis.

Which horses are especially susceptible to mite infestations?

A healthy horse won't be bothered by a few mites, but horses with weakened immune systems are susceptible: the bodies of very young horses and old, sick, or stressed animals cannot mount adequate defences against attacks from mites. If the horse's immune system is strained from moulting, a change of stable or the transition from the stable to the pasture, its defences against parasites are diminished. Underweight and/or malnourished horses are also frequently affected. A deficiency of zinc and vitamin A causes the skin barrier to weaken, allowing mites to settle.

Pre-existing skin conditions like sweet itch or mud fever, as well as metabolic disorders like EMS or PSSM will make a horse more susceptible to mite infestations.

How to combat mites?

Mites multiply rapidly – the earlier the horse gets treatment, the better! Massive mite infestations must be treated with chemical antiparasitic pastes. Vet-prescribed salves, sprays or even special shampoos can be used for topical treatment.

A natural alternative for localised treatment against Chorioptic mange mites is a mixture made of flowers or sulphur (available in powder form) and olive oil. This oil-sulphur mixture turns grey hair yellow and smells like rotten eggs, but is quite effective at repelling mites. Itching can be relieved with poultices or washes using calendula, camomile, or mallow tea. Infested horses should have their feathering clipped and the hair on the legs shorn to deprive mites of their habitat. This makes treatment easier as well! Mild herbal oils with lavender, camomile and speedwell extracts soothe irritated skin and facilitate post-treatment. Zinc salves with anti-inflammatory herbs like camomile promote the healing of wounds.

Applying oils, e.g. coconut oil or oils with herbal additives, is also often recommended as a way to suffocate mites. Mites breathe through pores which can be clogged with oils or soapy water. Herbal oils that contain lavender can even cause mites to flee – they hate the smell!
Caution: Some horses have reactions to topical oil treatments, including hair loss!

But treating an afflicted horse is only the beginning. Because mites also colonise a horse's environment, all of its items must be treated as well. Tack and grooming items must be disinfected, and the box of the infested horse must be thoroughly cleaned and ideally kept vacant for a period. The mites that hatch later from the eggs must also be killed, so follow-up treatment is necessary to prevent renewed outbreaks.

Kieselgur (diatomaceous earth) is a proven means of eliminating mites for those who would rather avoid strong chemicals. This fine, white powder is applied to places where mites dwell and desiccates them.

Caution: Kieselgur is hazardous to the respiratory organs of both humans and horses! Always wear a face mask when "fogging" the stable. Keep the horses out of the area until the dust has completely settled, which may take several hours. Do not use kieselgur in closed areas! 

How can I combat mites preventively?

Stabling and care

• Pay attention to stable hygiene
• Clean grooming items, tack, and rugs regularly. Each horse should have its own tack and grooming supplies!
• Avoid wet, cold stable conditions
• Keep feathering well groomed and clip during wet periods

Feed your horse a balanced diet

• Feed according to need
• Avoid high-sugar, high-starch feeds to help prevent metabolic disorders and a weakening of the organism
• Boost metabolism with herbs to promote skin metabolism: milk thistle, dandelion, and birch leaves support the detox organs and help to eliminate toxins.

Ensure an adequate supply of vitamins and minerals

A deficiency of zinc and vitamin A can facilitate parasite infestations, so susceptible horses should be given quality mineral feeds. B vitamins promote regeneration of the skin.

Boost your horse's immune system

During times when your horse's organism is under strain, keep it strong with immunity boosters from nature. The active substances in echinacea and the vitamin C in rose hips help to strengthen your horse's immune system. Grape seed oil and aronia berries are antioxidants and protect the cells. Mites won't have a chance against a strong immune system!

Sources and further reading

• Parasitenportal. (23. 03. 2021). Von Milben: https://parasitenportal.de/parasiten/milben/ abgerufen
• Vanselow, R. U. (2005). Pferdweide - Weidelandschaft. Hohenwarsleben: Westarp Wissenschaften-Verlagsgesellschaft.
• vtg Tiergesundheit. (23. 03 2021). Von Räude/Milben bei Pferden: https://www.vtg-tiergesundheit.de/ratgeber/raeude-milben-bei-pferden abgerufen
• vtg Tiergesundheit. (23. 03 2021). Von Ursache für Krankheiten: Milben: https://www.vtg-tiergesundheit.de/ratgeber/krankheitsursache-milben-bei-pferden abgerufen