I think you want Arthur C. Clarke's 1951 novelette "Second Dawn", first published in Science Fiction Quarterly, August 1951, available at the Internet Archive. That story was the subject of this old question and also this one, but I'm afraid the previous answers don't have enough detail about the story for a positive identification as the answer to your question.
Here is Clarke's description of the anatomy and culture of his aliens:
Jeryl and Eris came of a race which, in Nature's lottery, had been luckier than most—and yet had missed one of the greatest prizes of all. They had powerful bodies and powerful minds, and they lived in a world which was both temperate and fertile. By human standards, they would have seemed strange but by no means repulsive. Their sleek, fur-covered bodies tapered to a single giant rear-limb that could send them leaping over the ground in thirty-foot bounds. The two forelimbs were much smaller, and served merely for support and steadying. They ended in pointed hoofs that could be deadly in combat, but had no other useful purpose.
Both the Atheleni and their cousins, the Mithraneans, possessed mental powers that enabled them to develop a very advanced mathematics and philosophy; but over the physical world they had no control at all. Houses, tools, clothes—indeed, artifacts of any kind—were utterly unknown to them. To races which possessed hands, tentacles, or other means of manipulation, their culture would have seemed incredibly limited; yet such is the adaptability of the mind, and the power of the commonplace, that they seldom realized their handicaps and could imagine no other way of life. It was natural to wander in great herds over the fertile plains, pausing where food was plentiful and moving on again when it was exhausted. This nomadic life had given them enough leisure for philosophy and even for certain arts. Their telepathic powers had not yet robbed them of their voices and they had developed a complex vocal music and an even more complex choreography. But they took the greatest pride of all in the range of their thoughts; for thousands of generations they had sent their minds roving through the misty infinities of metaphysics. Of physics, and indeed of all the sciences of matter, they knew nothing—not even that they existed.
Our heroes make the acquaintance of another species called the Phileni:
It was a little creature, scarcely half their height, and it did not hop, but walked upon two jointed limbs that seemed very thin and feeble. Its large spherical head was dominated by three huge eyes, set far apart and capable if independent movement. With the best will in the world, Jeryl did not think it was very attractive.
Then Therodimus uttered another whistle, and the creature raised its forelimbs toward them.
"Look closely," said Therodimus, very gently, "and you will see the answer to many of your questions."
For the first time, Jeryl saw that the creature's forelimbs did not end in hoofs, or indeed after the fashion of any animal with which she was acquainted. Instead, they divided into at least a dozen thin, flexible tentacles and two hooked claws.
The two species enter into a partnership:
"We have developed our minds, and our minds alone, until we can go no further. As Aretenon has told you, we have now come to a danger that threaten our entire race. We are under the shadow of the irresistible weapon against which there can be no defense.
"The solution is, quite literally, in the hands of the Phileni. We must use their skills to reshape our world, and to remove the cause of all our wars. We must go back to the beginning and re-lay the foundations of our culture. It won't be our culture alone, though, for we shall share it with the Phileni. They will be the hands—we the brains.
All right, so the aliens aren't very horse-like, and their handy assistants aren't all that humanoid. Do you think this could be your story anyway?
