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Every stallion owner’s worst nightmare: 2 months into the breeding season and your stallion is not settling his mares.  His bloodlines are impeccable, and he had a great start to his performance career so this year you offered to stand him at stud to outside mares, and the response has been great, 40 mares booked in his first season!  As a responsible and experienced stallion owner, you had a breeding soundness examination done and he passed with flying colors; good testicular size, good sperm production, good motility, concentration and morphology and his semen responded very well in a 48-hour cooled semen trial. He should be able to handle a book of 40 mares without problems.  So why isn't he settling his mares?

Those of us who work with stallions are routinely asked to determine a stallion’s fertility prior to breeding mares or to investigate the cause of low fertility. Often this requires sending the stallion to a specialized veterinary clinic or a veterinary school. Advances have been made in stallion fertility evaluations through the use of computerized sperm motion analyzers (CASA) and flow cytometry.

Diagnosis of infertility in stallions usually starts with a complete reproductive history and then collection of semen to evaluate seminal parameters, testis size and the potential presence of bacteria in the semen. A more detailed evaluation might also include drawing blood for hormonal analysis.

Knowing and keeping track of the concentration, or the number of sperm per milliliter, of each ejaculate for a stallion is very important for a variety of reasons. The concentration of his semen, along with the volume of his ejaculate, is used to determine the total number of sperm he produces in a given collection. These two numbers (volume and concentration) are used to calculate insemination doses. Also, keeping a record of each number can help stallion managers recognize if there are any changes in the reproductive health of the stallion. Slight variations are likely nothing to be concerned about. However, if the number of sperm in the ejaculate varies drastically, from collection to collection or a steady decrease in his total number of sperm over time, one may begin to ask what is causing the change. This information is valuable so that any concerns can be addressed as soon as they arise.

Shuttle or Dual-Hemisphere Stallions are terms used to describe breeding stallions which travel between the Northern and Southern Hemispheres for their respective breeding season. Several questions arise when discussing shuttle stallions and may include: Why do stallion owners incur the costs and risks of sending their stallions thousands of miles away? Does the lack of sexual rest affect their fertility? Is there a way to service mares in a different hemisphere without sending the stallion so many miles away?

To understand why seminal plasma is beneficial in some situations and potentially harmful in others we must first review what it is, where it comes from and what we think are its roles in reproduction. The term seminal plasma refers to the fluid portion of ejaculated semen in which the spermatozoa are suspended. This fluid consists of secretions from the accessory sex glands in the stallion’s reproductive tract. These include the ampullae, the vesicular glands (seminal vesicles), the prostate gland and the bulbourethral glands (figure 1).

Once young colts and fillies reach the age of puberty their behavior may become an issue in the show ring or on the race track. Castrating a colt which you intend to use for breeding purposes may not be an option and mares are not typically permanently sterilized. Their sexual behavior may also cause problems with housing, trail riding, etc. In this article, Dr. Ed Squires discusses some of the common ways stallion and mare owners suppress the behavior of their horses.

For most facilities, using a phantom is the preferred method of collecting semen from a stallion, as it is an efficient, organized and generally a safe process that mimics the natural position during live breeding. Ground semen collection (see video below) is an alternative option to the typical collection of a stallion on a phantom or mount mare.  This article describes ground semen collection, primarily summarizing previously published clinical and research reports of Sue McDonnell and colleagues at the University of Pennsylvania and Jim Crump of Roanoke AI.

There are many reasons and techniques for collecting a fractionated ejaculate from a stallion. In this article we will discuss some reasons why and demonstrate the technique we have used in our laboratory to manage a stallion with excessive gel fraction that contaminates ejaculates collected using standard in-line filter equipment.

Juvenile and older males entering a new career as a breeding stallion don't have the luxury of a changing cascade of hormones or an event like parturition to jumpstart their innate nature to show them how to be a stallion. There is likely only a change in routine, location, or in their training schedule that cues them into their new roles as breeding animals. Many stallions make the transition seamlessly. Simply acting on the behavior they have been trying to use for years, allowing their behavior to mimic their springtime rise in testosterone. When exposed to a female, they have little doubt about the job at hand and will readily take to live cover or phantom training. Additional information for training the young stallion for collection can be found in our article, Collecting Semen from the Young Stallion. However, for some, the transition proves far more difficult and oftentimes frustrating for the stallion and for the staff at the shed.