Complex sentence: Stallions with white markings other than a small star are not eligible for licensing by the Highland Pony Society, which actively discourages white markings of any description other than the small white star.
Split into simpler sentences: Stallions with white markings other than a small star are not eligible for licensing by the Highland Pony Society. The Highland Pony Society actively discourages white markings of any description other than a small white star.