Soooo.....in humans if you are a twin or your mother had a set of twins, or you have many twins in your family,etc. You are more likely to have twins yourself (some,but not all types of twins are hereditary)
Then....in chimeric horses the same thing happens....twins are believed to have fused. So in these brindles stallions producing "brindle" offspring couldnt they really just be chimeric because even though chimeric isnt "heridetary" the chance of having more sets of twins IS and thus have a much higher chance of producing twins. And a higher chance of them fusing to produce chimeric?
So it kinda makes the chimeric somewhat hereditary anyways?
I hope this makes sense....lol...