What is an Allergy?

From Wikipedia: “An allergy is a hypersensitivity disorder of the immune system. Allergic reactions occur when a person's (or animal’s) immune system reacts to normally harmless substances in the environment. A substance that causes a reaction is called an allergen.

These reactions are acquired, predictable, and rapid. Allergic reactions are distinctive because of excessive activation of certain white blood cells called mast cells and basophils by a type of antibody called Immunoglobulin E (IgE). This reaction results in an inflammatory response which can range from uncomfortable to dangerous.

Mild allergies like hay fever are very common in the human population and cause symptoms such as red eyes, itchiness, and runny nose, eczema, hives, or an asthma attack. Allergies can play a major role in conditions such as asthma.”
Some allergies are mild, while others can be life-threatening.  Allergens can be air-borne, like pollens, or spores or moulds in the soil/grass environment. In addition, certain foods, feeds, grains, hay, nutrition supplements and insect bites can also trigger allergic reactions.

Which ‘Allergens’ most commonly affect horses?

The most common are Pollens from:
Trees: Pines, Birches, Alders, Cedars, sometimes Willows, Poplars and Plane Trees
Grasses: Rye-Grasses, Poa’s and Timothy
Some weeds can also be classed as allergens
Fungal Spores: are potential allergens easily breathed up the nasal passages along with pollens, whilst the horse grazes.
Dusty Hay or Bedding : should be easy to identify. Change hays or dunk it to eliminate dust

Problems Caused by Allergens

 ‘Runny Noses’ and ‘Watery Eyes’
These are some of the first signs of allergies. They are common in grass fed horses and symptoms tend to come and go.  
Histamines either present in the plants, or produced by the horse in response to allergens in the environment, cause an increase in permeability of both the little blood vessels and cell membranes of affected tissue. This increased blood vessel permeability causes fluid to exit from capillaries into the tissues, which leads to an allergic reaction: a runny nose and watery eyes.

Allergic Rhinitis
The nasal membranes of your horse should be ‘salmony pink’, smooth and clean looking. On a sunny day hold the nostrils up towards the sun and have a good look. If they look inflamed, bumpy, yellowy or ulcerated then your horse likely has ‘Rhinitis’. (The first line of thought is often ‘Herpes’ but swabbing proves negative)
Rhinitis is caused by breathing up fungal spores and pollens whilst the horse is grazing. Think about it: their nostrils are down there about 18 hours per day so there is plenty of opportunity for this to happen.
This irritation of the nasal membranes may cause your horse to do a lot of snorting especially when you commence exercise. They may also do a ‘clearing cough’ when you first start trotting or cantering.
Applying a small amount of vaseline around the nostril opening may help reduce exposure.
If the symptoms get worse and start to affect their breathing it has progressed to ‘Pasture Heaves’ a condition very similar to ‘Asthma’.

 

Histamines

It is Important to Understand the Role of Histamines:
Histamine is a very important neurotransmitter that primarily regulates the body thirst mechanism for increased water intake. It also controls rationing of the available water stores in the body during dehydration. So histamines are called up to help but end up causing trouble when they are over-produced

Salt Deficiency

• According to Dr. F. Batmanghelidj in "Your Body's Many Cries for Water," a salt shortage in the body can trigger a histamine reaction. Basically, the body is trying to preserve fluids for vital parts of the body like the brain, lungs and liver. Lack of water or salt can cause an overactive histamine reaction which produces allergy-type reactions.
• Dr. Batmanghelidj says salt is a natural antihistamine. It will help stop the over-production of histamines

Histamines also cause:

• Cell membranes and blood vessels to become more permeable
• Smooth muscle to contract/spasm

Here is some more information on Histamines
From the Colombia Encyclopedia:
histamine; organic compound derived in the body from the amino acid histidine by the removal of a carboxyl group (COOH). Although found in many plant and animal tissues, histamine is specifically important in human physiology because it is one of the chemicals released from certain cells (particularly mast cells) upon tissue injury or during the neutralization of foreign material (antigens) by certain types of antibodies.
Released histamine tends to dilate blood capillaries, often causing the skin to appear red and feel warm, and makes the capillaries more permeable, allowing fluid to escape into the tissues. This causes edema (swelling), usually manifested as acute urticaria (rapidly appearing hives, accompanied by severe itching). This sort of reaction is common to many allergies, such as food allergies, and the symptoms can often be controlled well with antihistamines. Unfortunately, histamine is not the only substance released under these conditions, and some allergies, particularly chronic ones such as asthma, are relatively resistant to antihistamine therapy.

From the Saunders Veterinary Dictionary:
It induces capillary dilatation, which increases capillary permeability and lowers blood pressure; contraction of most smooth muscle tissue; increased gastric acid secretion; and acceleration of the heart rate. It is also a mediator of immediate hypersensitivity.

Histamine is a chemical that our body releases when it needs help correcting a shortage of some very important substances like water, salt or potassium. Histamine will help re-balance the body that is "out of balance". Histamine is really a good thing that saves our lives according to the great Dr. F. Batmanghelidj. The medical field today is using anti-histamines because it does not understand how histamine really works in the human body.

Did you know?

Histamines are also found in some plants, notably rye-grass and clover.
The role of histamine in plants is as a chemical defense against herbivores. Plants contain thousands of defensive chemicals. Substances like histamines are not involved in growth of the plant but are meant to discourage consumption by herbivores.  (Other such compounds include caffeine, nicotine and cocaine!)
We all know not to touch various ‘Nettles’ especially stinging nettle because they contain several irritant chemicals including histamine. Contact with stinging nettles causes a skin irritation and histamine seems to be the culprit.
(Incidentally histamine is also found in tomato and citrus.)

What can I do?

What does help if your horse is suffering from Respiratory Allergies?

Short term

Magnesium will promote relaxation and dilation of the smooth muscle lining the airways thus helping to counteract the ‘constriction’ caused by the presence of histamines.
Vitamin C can assist with lowering histamine production so that allergies are less likely to trigger an asthma attack. The antioxidant effect of Vitamin C helps protect the lungs and airways against free radical damage.
Vitamin B6 – is present in the Premium NZ Horse Minerals and will also be produced by the hind-gut flora when the horse eats plenty of hay.
Omega 3’s – linseed or flax-seed oil is a good source of Omega 3’s.

Use of an ‘Inhaler’ from your Vet can sometimes provide temporary, immediate relief short term.

Long term

Managing your horse’s grass intake and taking other steps outlined to avoid dietary imbalances including the long term feeding of salt show the most promise for afflicted horses.

For respiratory conditions it is definitely a case of ‘an ounce of prevention is worth a ton of cure’.