You might be interested in past posts on the topic:

• Were there known instances of 'breeding' slaves for certain traits/purposes during North American slavery?
  ^(03 Feb 2013 | 41 comments)
  ^(answered by /u/Talleyrayand)

• Selective Breeding During American Slavery
  ^(14 Dec 2015 | 2 comments)
  ^(/u/sowser discusses possible evidence for the practice.)

You can ask followup questions by commenting with the question and username of an expert in the body of your comment, directing it towards them with a mention.