It's a good question, but there is more to it than hiring extra horses:
More horses can help to produce more fodder, true. In order to grow more fodder you need not only more horses but also more manure. Since you don't have more horses (and/or manure) you can't grow more fodder. That's what limited agriculture until the industrial revolution.
The industrial revolution made more and better mechanical equipment available to assist horses first, and replace them later on. Following and during the industrial revolution we have another revolution: the chemical revolution. That's when artificial fertilizer became available and affordable.
The artificial fertilizer is more important than horses when you want to raise food production. Theoretically you can import extra horses to plow more fields. Those fields have to be fertile enough to support crops. If those fields were fertile, they would have been under the plow already.
Thus, you need to make them more fertile with additional fertilizer after plowing. Which means having to import not only horses, but also manure. Which was, apart from being smelly, fairly expensive and in limited supply. Artificial fertilizer created with inorganic chemistry made that possible and more important: affordable.
Yes, you can import both horses and manure. But then the cost would become prohibitive. That's the other limitation: the food/fodder must be affordable as well.
Before the industrial revolution the republic of the United Netherlands, particularly the province of Holland, was the most heavily industrialized area of the world. The horse wasn't that important. Since distances in Holland are relatively very small and the country is somewhat wet, the barge was used for transporting goods, not so much horses and carts. Holland didn't grow much food or fodder. They bought it from elsewhere. Holland is also a windy country, so they used that power with windmills - where the word mill (as: 'factory mill') comes into action. They solved their problem not by importing or hiring more horses, but using a very different method to overcome their problems.