Related to this M.Y. question, which I relayed to a friend, he suggested asking this related question:
וְי֙וֹם֙ הַשְּׁבִיעִ֜֔י שַׁבָּ֖֣ת ׀ לַיהוָ֖֣ה אֱלֹהֶ֑֗יךָ לֹ֣א תַעֲשֶׂ֣ה כָל־מְלָאכָ֡ה אַתָּ֣ה וּבִנְךָֽ־וּבִתֶּ֣ךָ וְעַבְדְּךָֽ־וַ֠אֲמָתֶךָ וְשׁוֹרְךָ֨ וַחֲמֹֽרְךָ֜ וְכָל־בְּהֶמְתֶּ֗ךָ וְגֵֽרְךָ֙ אֲשֶׁ֣ר בִּשְׁעָרֶ֔יךָ לְמַ֗עַן יָנ֛וּחַ עַבְדְּךָ֥ וַאֲמָתְךָ֖ כָּמֽ֑וֹךָ׃
but the seventh day is a sabbath unto the LORD thy God, in it thou shalt not do any manner of work, thou, nor thy son, nor thy daughter, nor thy man-servant, nor thy maid-servant, nor thine ox, nor thine ass, nor any of thy cattle, nor thy stranger that is within thy gates; that thy man-servant and thy maid-servant may rest as well as thou.
Note: - The English translates וְכָל־בְּהֶמְתֶּ֗ךָ as "thy cattle". This may be a loose / vague translation. In particular, Meshech Chochma commentary states that this phrase includes birds, which are certainly not cattle.
According to Rabbi Ishma'el's 13 Hermeneutical principles, we have in this verse a case of פרט וכלל - a specific list, vis., "Ox and ass" followed by a generalization, vis., וְכָל־בְּהֶמְתֶּ֗ךָ. When this situation occurs, the rule is that the generalization comes to include all other animals in the same category.
So, considering this rule in combination with what Meshech Chochma included, would horses, or any animal, for that matter, be prohibited from ding melacha on Shabbat?