Stabilization of extragonadal sperm reserves in stallions: application for determination of daily sperm output

摘要

In order to accurately predict the number of mares a stallion can breed during a given time period, it is necessary to know the number of sperm in ejaculates when the stallion is actively breeding. Once extragonadal sperm reserves (EGR) are stabilized, the number of sperm in ejaculates can be used to estimate daily sperm output (DSO). Colorado workers found that 5-7 consecutive days of ejaculation are required in sexually rested stallions to deplete EGR [1], and therefore suggested collecting semen once daily for 2 weeks and averaging the number of sperm in ejaculates obtained during the 2nd week or, alternatively, using the number of sperm in the ejaculate on Day 7, as representation of DSO [2,3]. Texas workers have recommended once daily collections for 10 days, averaging the number of sperm in ejaculates collected on Days 8-10 to represent DSO [4]. In another study, the numbers of sperm in ejaculates on Days 5-7 were averaged to determine DSO [5]. Due to time and cost constraints, lengthy collection protocols are often impractical. It is unclear whether the number of days of once daily ejaculations required to reach DSO varies with testicular size. This trial was performed to evaluate the influence of testicular size on the number of consecutive days of semen collection required to stabilize the number of sperm in ejaculates of sexually mature stallions.