All modern light horse breeds carry the blood of the arabian. IMO they are the only breed that is known to successfully cross on most others.
They are also the purest breed and a different subtype wth less vertabraes, tail bones aned ribs than other breeds. Some mustangs aslo have this trait. Especally thse of almost pure spainich blood. Infact if you ask me I think the only 2 crosses acceptable for a mustang are the Arab and maybe the Andulusaion.
I did see an Andulsion Kiger cross. Looked like an Andulsion dun. I did breed my Arab stallion ot a mustang mare this year. They are hoping for an endurance prospect. Shalom