What is meant by "it is permissible if the covering is controlled by number of times, or by a specified time, though it is disliked" in the context of the prohibition of selling stud services of a camel?

The origin of this issue relates to the conditions of sale, and that the sold item must be in existence at the time of the contract. Therefore, selling a non-existent item is void. An example of this is selling what is in the loins of male animals (their breeding). The Malikis have permitted leasing a male animal for breeding if the lease is for a specified period or for a specified number of times. It is not permissible to lease a male animal until the female becomes pregnant. If pregnancy occurs before the end of the period or the number of times, the lease is terminated, and the owner of the female must pay the rent for the time or times that have passed. Al-Adawi mentioned in his supercommentary on Sharh Kifayat al-Talib al-Rabbani the permissibility of mating for a specified number of times or period, and that prohibiting it is disliked (makruh), and that taking payment for it is not among noble character traits (makarim al-akhlaq).