To the mare owner, he’s handsome on the video, and in person, he’s virile—but what’s this stallion’s record in getting mares pregnant? To the stallion owner, how does this horse measure up under the microscope—and build his reputation as a sire?
No matter how attractive the stallion, he’s only successful as a breeding stallion if he sires foals. Producing a foal depends on how reliably he puts out spermatozoa that can fertilize the mare’s egg. To evaluate that output and to maintain the breeding stallion, it is often helpful to enlist the aid of an equine practitioner.
One such individual is Lisa Metcalf, MS, DVM, who operates Honahlee PC, an equine reproduction center in Sherwood, Oregon. “All my clients routinely test stallions in extenders, for fresh semen, and for the best management techniques for that stallion,” says Metcalf, who is also a Diplomate of the American College of Theriogenologists.
Whether the stallion breeds by natural cover or artificial insemination (AI), his sperm quality is what defines his success. Every stallion is unique—you evaluate his breeding soundness through a series of evaluations of the ejaculate you collect. To examine a stallion’s data, let’s see what goes on after the breeding shed—in the laboratory.
Evidence of Viable Sperm
If you’re the stallion manager, you begin appraising a stallion’s sperm by inspecting both the raw ejaculate and the extended semen samples. Diluting the ejaculate with an extender protects the sperm and therefore lengthens its life for short-term storage or transport.
Start by determining the concentration of the ejaculate. You can count millions per milliliter (M/ml) by using one of two instruments:
1. Hemacytometer. This device is used to determine cell concentration, along with a microscope to count the cells. Ideally, the concentration of raw semen should be 100 M/ml, at a minimum.
2. Spectrophotometer. This automated, more powerful instrument speeds up the process, but at some cost in accuracy. Jos Mottershead
of Equine-Reproduction.com notes, “These devices are not as accurate as the hemacytometer, as well as being more expensive, although more convenient.” Many devices are based on the spectrophotometer, including Accuread, QuickCheck, DVM Stat, and Counterpoint.
For breeding with AI, you’ll likely use extended semen. Mottershead explains, “ The aim is to obtain a final diluted sperm concentration between 25 M/ml and 50 M/ml. With the Kenney extender, one of the most common, a minimum extender-semen dilution ratio is 3 to 1, and preferably 4 to 1.” To reach the optimal concentration, the ratio of the dilution can vary, because the stallion’s sperm production may be inconsistent.
“It is essential to count each ejaculate,” Mottershead says. “Some people get one ejaculate counted by a veterinarian, and then attempt to use the same concentration from then on. There can be a tremendous variation between ejaculates.”
A proper count is essential to determine the proper dosage as well. Bo Crabo, DVM, Cave Creek, Arizona, adds, “For frozen semen, you need approximately 1 billion sperm cells in the dose, or at least over 800 million.” And the count should be done quickly. Hamilton Research, Inc., manufacturer of the Equitainer, recommends extending the sample within 10 minutes of collection. The extender itself should be heated to 37°C.
The next inspection is for motility. Metcalf explains, “You need a fairly good microscope, and the ability to heat the extended sample to 37°C (body temperature) to evaluate motility accurately.” Under the microscope, look for progressively motile sperm—seeing that at least half are swimming forward and in a straight line, not in circles or backward. Recognize, though, that motility is a tool, not a guarantee of a stallion’s fertility. “Motility is an indication, but it’s not really correlated with fertility,” says Metcalf. “It’s a poor correlation.” Crabo agrees, calling the motility-fertility connection “a sad story.” Relying on reports of motility can lead to disappointment.
Factors Beyond Motility
For fertility, the sperm must be both viable and able to impregnate the mare upon arrival of the egg. Therefore, when you’re in the lab looking at sperm, you need to look for more than movement: the normal shape of sperm, and how to estimate their longevity to make it through transport.
Normal shape. “Morphology is better correlated with fertility than motility,” says Metcalf, along with “composition and fluidity of the plasma membrane.”
Crabo explains, “Essentially, in fertilization, the sperm membrane and the egg membrane fuse. The egg engulfs the sperm. Therefore, the condition of the membrane is really important.” He adds, “There is seminal plasma there that can inhibit the sperm fertility.” Choosing the right extender for the stallion can influence the effect of this plasma.
Longevity. You can’t predict by visual inspection how long sperm will live in storage prior to insemination. Re-examining samples at scheduled intervals is the only way you can estimate the longevity of a stallion’s cooled semen.
If the stallion is to breed through frozen semen, he must be able “to freeze.” Frozen semen is processed with a cryopreservation agent, which also influences the ability of the individual’s sperm to inseminate the chosen mare.
Despite the variables, breeding through frozen semen has a major upside:?it increases a stallion’s opportunities, with nearly the same success rate as AI. “Pregnancy rates have definitely increased with frozen semen, so much that we are now at the point of appointment breeding,” says Metcalf.
Proper Handling After Collection
Even if the stallion produces quality sperm, AI management can affect the chances for conception. “Many of the problems I see with ‘abnormal’ stallions are actually corrected with improved management,” says Metcalf. “Sperm are very sensitive to light, cold, heat, and other environmental factors. We need to realize how sensitive the sperm are to these factors to minimize damage.”
When collecting a sample in a very hot or cold climate, be aware that “ambient weather conditions can play a part,” says Mottershead. Temperature is important—not too hot, and not chilled on the way to the lab. (By the way, your lab could be the kitchen of your house.) Once semen is collected, commercial reproduction services can evaluate it. These specialty companies use top-level equipment for authoritative, objective analysis.
“If you have a stallion with a fertility problem, you should consider sending a sample to a lab that has state-of-the-art equipment, such as computer-assisted motility analysis and flow cytometry,” advises Metcalf.
It’s a good idea to evaluate a sample before every breeding season. Mottershead believes this annual checkup is vital, even if the stallion has established a good record in fertility. “To look at evaluating for the correct extender, we recommend to do that prior to the first shipment. There’s no guarantee he’ll ship the same this year.” He adds, “If you find the viability isn’t lasting for the same duration as you want, maybe another extender would work better.” To gauge the quality of shipped semen, keep samples to inspect at both 24 hours and 48 hours after collection. Mottershead also advises a test at 72 hours as well, especially if shipping to a region without overnight delivery, or when the mare’s ovulation date could be unknown. “Some people may be happy with 30-percent motility at 96 hours, but remember that motility does not equate to fertility,” he says. Mottershead also suggests to mare owners to invest in their own Equitainer. That reduces cost over the years, and assures consistent quality of shipment. Stallion managers can learn techniques for handling semen through attending short courses. Colorado State University is a well-known source for such training.
Managing for Fertility
Beyond careful handling, the stallion requires methodical management. He can be treated pretty much like any other horse when it comes to nutrition, exercise, veterinary treatments, and hoof care. However, one nutritional product, Magnitude, has been shown to improve the motility and “shippability” of a stallion’s semen. This feed supplement for stallions contains omega-3 fatty acids and supplies Docahexaenoic Acid (DHA), important in sperm development.
Management of the stallion’s lifestyle is more critical, because lifestyle can greatly influence sperm quality, especially when training and showing. “With some stallions in heavy work, we suspect that the testicles heat up so much that you don’t see top quality semen,” says Metcalf. “So you might offer breeding with frozen semen of good quality during that time.”
With working stallions, it may take 60 days before their sperm quality is back to normal. However, she adds, “I have a number of stallions who have no problem with being collected in the morning, and jumping a Grand Prix course in the afternoon.”
The solution is simple enough:?work the stallion in a manner that sustains his sperm production. “Every stallion is different,”?says Metcalf. “If he’s used infrequently, it is important to keep his extragonadal sperm storage reserves flushed out so you always have the best quality semen for shipment.” She adds, “Some stallions tolerate collection every day, others only two times per week.” On the other hand, says Mottershead, a stallion that’s used too often could “deplete his gonadal reserves.” He notes that most stallions will not have this problem, because the demand isn’t that great for their semen.
Eventually, all stallions lose potency. Typically, quality starts to decrease around age 13. Of course, individuals vary, with some 8-year-olds dropping in quality, while some 20-year-olds are still going strong.
For the mare owner investigating a stallion’s production, what’s most important are the chances for conception. Mottershead advises asking about first cycle conception rate, and the EVA status of the stallion. For the first cycle conception rate, he says, “for on-farm AI or live cover, you should see something in excess of 65 percent; shipped, 55 percent; and frozen, 45-50 percent.”
For anyone managing a breeding stallion—or the mare owner investing in a stud fee for a planned foal—quality is what makes a stallion valuable. The number and quality of his progeny establish his reputation as a proven producer.