Slaves were dispensable, whereas horses and oxen were costlier. [fact]
As long as imported African labour was relatively cheap to replenish, planters could afford to use people rather than animals to perform the most back-breaking tasks. After all, slaves were dispensable, whereas horses and oxen were costlier to import and less likely to survive in the unforgiving climate.
Stella Dadzie, A Kick in the Belly- Women,…, loc. 186