I have never heard of giving eggs to horses. Never read it in any feeding programs on the net. But to get the best source of protein laid down into your horse's condition, we use soy bean meal. Up to a cup a day for a horse mixed into your feed. Works a treat and it has the highest usable amount of protein (43%) as opposed to something like linseed which is not as good and can cause other problems. It is relatively cheap too, as you don't give too much to get a good result.