I raced a bitch in the early 90s she broke track records and won bend and straight championships.
People used to slag me over for what they called giving her too much.I would enter her in her weight class and if there was a 10yd dash on she wud go it that as well.Sometimes i wud put her in a no limit or up to 40lb scratch race too.
The trick is to keep them injury free,not to difficult with racing as long as the ground isnt to hard,but coursing is a different ball game,suddenly changing direction causes a lot of stress on feet and joints
So i would say it depends how serious u are about rac