Also BTW, did you know that Brazil imported 11 times as many slaves as America did? (4.9 million vs 0.305 million, source Wikipedia).
Yes, and the conditions of slavery in Brazil were so bad that far fewer slaves produced offspring.
In Brazil, it was cheaper to work slaves to death, then buy replacements, than it was to allow the slaves to procreate.
In the U.S., slaves were encouraged to be Christian, to marry, to have children.
Yes, there were lots of exceptions, but marriage and children for slaves were the norm.
http://spartacus-educational.com/USASmarriage.htm