Industry - sentient or otherwise - no longer uses use horses anymore because their productivity per unit cost is lower than machines. They were never smart enough to produce more than brute force value. In small numbers they are able to earn their keep as entertainment sources and pets.
Their population is largely function of their ability to provide utility in those two domains, plus wild numbers we protect in response to mostly our aesthetic tastes.
What will become of humans once our productivity per unit cost is significantly lower than AI? This could come soon. If it comes, it could easily be the one of the most important issues humans have ever faced. Keep in mind that your normalcy bias is shouting at you that that it will never happen.