There are 6 allergens associated with an allergy to horses, this includes their hair, dander (which is flakes of dry skin), urine and saliva.
Equ c 1 and Equ c 2 are lipocalin proteins, in other animal dander allergies this is the protein that most individuals react to. These proteins transport molecules like lipids and steroids around the body.
Equ c 3 is a serum albumin protein, people who are allergic to this protein are more likely to be allergic to other mammals and very rarely can become allergic to eating mammalian meats such as beef, chicken and pork, which also contain these proteins.
Equ c 6 is a lysozyme which is a contact allergen and is also found in donkeys and chickens.
I have put together some more comprehensive resources at http://www.allergyresources.co.uk/Horse.php
The allergy resources page for horse covers the key allergens, which allergic syndromes are linked to this allergy and other foods which are commonly cross reactive with horse hair.
There is also regularly updated links to useful websites specifically for horse hair allergies and the latest research papers on the topic.
If you have multiple allergies and are interested in how they are linked or want to find out more about food allergies outside the usual top 14 then you can follow me on Facebook or Twitter, where I share a food allergy card every day of the week.