The Prophet ﷺ forbade taking payment for the stud service of a male animal.
حدثنا إسماعيل حدثنا علي بن الحكم عن نافع
أن النبي ﷺ نهى عن ثمن عسب الفحل
Its isnad is sahih. Ali bin Hakam is Banani. Bukhari, Abu Dawud, and Nasai narrated this hadith, as in Muntaqa 2785. Asb al-fahl, with a fatha on the ain and a sakin on the sin, means the stud animal's semen, whether horse, camel, or otherwise, and taking payment for that is forbidden.