Were slaves considered animals

Not exactly. It's a bit more complex. American slaves were literally property, and some slave owners may have considered their slaves livestock. But, slaves were a considerably greater investment, both purchase and daily care and keeping than even the most expensive breed of horse.

During the American Civil War, horses were purchased for an average $150.00, whiles slaves were routinely sold for more than $2,000.00. During the same period, the average household income was around $1,800.00 a year.