Even now, a properly raised racehorse is prohibitively expensive.
In the past, when horses were used for everything from simple racing to transportation to combat, the value of horses was higher than it is now, but never lower.
Until modern times, the reason why large cavalry = a symbol of a powerful army was because it was impossible to raise and train those expensive war horses in large quantities except for nomadic tribes or quite powerful countries (and even for those powerful countries, there were cases where it was impossible).
The value of horses on the battlefield was very high in the past because the value of war horses was absolute for transporting supplies in a time when there were no automobiles or armies that did not rely on cavalry.
But they slaughter it and feed it as meat.
In past war records, when horses were slaughtered and fed to soldiers, 99% of them were almost defeated or on the verge of surrender.
Representatively, during the Japanese Invasion of Korea, Kiyomasa Kato had his supplies cut off by the Joseon army during the Battle of Ulsan Fortress, so he endured miserably, drinking not only horse meat but also horse skin, and barely escaped.
Even during Napoleon’s Russian expedition, the retreating French army was so miserable that they even had to eat horse meat with gunpowder.
Even in the 20th century, during the Battle of Stalingrad in World War II, the German army slaughtered all the horses they had, fed them to their soldiers, and then surrendered to the Soviet army.