Allergy alert

Allergies are something most of us are familiar with to some extent, either in ourselves or our animals. Essentially, an allergy is a reaction by the immune system to something that is completely harmless, and horses can develop one in a similar way to people by reacting to substances found in their environment, feed or medication.

An allergic reaction is triggered when the horse comes into contact with an allergen, such as being bitten by an insect or inhaling pollen, and the cells of the immune system interpret this as a possible threat.

This starts a cascade of reactions within the body causing the production of antibodies, as well as the release of chemicals such as histamine and prostaglandins. These then cause body tissues to show the signs we see during allergy flare-ups, such as itchy skin, coughing and runny eyes.

A sensitive reaction

Before a reaction can occur, a horse’s immune system must become sensitised to an allergen, which means the immune cells must have encountered the allergen before, thereby allowing them to recognise it. Because of this, allergies are more common in middle-aged to older horses.

The reasons this sensitisation occurs is unclear. Some breeds, for example Welsh ponies, seem genetically predisposed to developing allergies, although this doesn’t necessarily mean it’s bound to happen.

Spot the signs

Signs of an allergic reaction vary according to the type of allergy, the allergen and the individual animal.

Skin reactions include…

• pruritus (itchy skin) – for example scratching, tail swishing, nibbling at the body or rubbing on fences
• urticaria/hives – bumpy swellings within the skin
• hair loss – especially from the mane and base of the tail, as well as any other areas that can be easily rubbed
• abnormal skin texture – often dry and scurfy before becoming sore and irritated with a thickening of the skin developing

Skin allergies don’t generally cause severe problems, but if the allergy is particularly bad or goes on for a long time, the horse can suffer wounds and secondary skin infections through trauma to the skin.

Respiratory reactions include…

• nasal discharge – often watery at first but becoming thicker while also changing colour (white, yellow or green)
• increased respiratory rate and effort (heaves) – may be mild initially, but can become true respiratory distress over time
• coughing – often dry, but some horses may cough up discharge
• head shaking
• reduced exercise tolerance

Respiratory allergies can become very distressing if the horse is severely affected, particularly when there’s a persistent cough or very laboured breathing even at rest.

Gut reactions include…

• diarrhoea
• colic

Gut reactions are normally mild and self-limiting, although in more severe or long-term cases, they can cause weight loss and permanent damage to the gut.

Find out more about equine allergies and how to manage them in July Horse&Rider – on sale now!