Learn Equine Semen Analysis
What semen analysis actually involves and what those percentages really mean.
Every breeding season, social media fills with posts like “The semen we got tested at only 10%—what can I do for a refund?” or “The vet said the semen was bad, I doubt my mare will get in foal.”
Before jumping to conclusions, it helps to understand what semen analysis actually involves and what those percentages really mean.
Why Your Vet’s Experience Matters
Most veterinarians receive only a brief introduction to equine reproduction during their training. Their focus covers many species, not just horses. Unless they complete extra study or a reproduction residency, their hands-on knowledge of equine breeding is limited.
That is why it is worth working with a specialist in equine reproduction. Their training and equipment are designed for accurate semen handling and analysis. Many mare owners learn this the hard way, after several breeding cycles with no success and no clear explanation why.
The Basics of Equine Semen
Stallion semen is delicate. It is easily damaged by heat, cold, or sunlight. The wrong temperature for even a few minutes can kill most sperm cells.
An ejaculate has three parts:
Pre-ejaculate, containing seminal plasma
Sperm-rich portion, containing the fertile sperm cells
Gel fraction, which is filtered out before processing
Under a microscope, a normal sperm cell has a head, a midpiece, and a tail. When examined, you will see live and dead sperm, those missing tails or heads, those swimming in circles, and some that just vibrate in place. Only the sperm with a full structure that swim straight or nearly straight are capable of fertilizing an egg.
Understanding Morphology and Motility
Morphology describes how the sperm cells look.
Motility describes how they move.
A morphologically normal sperm swims forward with good speed and direction. Those with bent tails, missing parts, or poor movement are considered abnormal.
When semen is processed for insemination, the lab must count both normal and abnormal cells to calculate how many viable sperm are included in each breeding dose.
Total Motility vs Progressive Motility
When you hear a percentage like 80% or 90% motility, it is important to ask what kind of motility is being measured.
Total motility counts every sperm cell that moves, in any direction.
Progressive motility counts only the sperm swimming forward in a straight or semi-straight line.
A stallion may show 80% total motility but only 60% progressive motility. Many people confuse the two. In reality, most stallions average between 50% and 60% progressive motility right after collection.
How Semen Is Evaluated
There are two main methods—subjective and objective evaluation.
Subjective evaluation uses a microscope and a sperm counter. The semen must be diluted properly so that individual sperm can be seen clearly. This method depends on the skill and experience of the person viewing it.
Objective evaluation uses a Computer Assisted Semen Analysis (CASA) system. This software measures movement and speed more accurately and helps prevent human error. CASA is considered the most reliable method for evaluating semen quality.
Calculating the Breeding Dose
Once concentration and volume are measured, the total number of sperm is calculated. From there, the lab works out how many progressively motile sperm are in the sample and how many doses can be prepared.
For example:
Concentration: 355 million sperm per millilitre
Volume: 40 mL
Total sperm: 14.2 billion
If progressive motility is 60%, that equals about 8.5 billion viable sperm.
Traditionally, each dose for cooled shipped semen contained at least 1 billion progressively motile sperm to allow for cell loss during transport. Newer studies show that even 200 million progressively motile sperm at the time of shipping can result in successful conception when insemination is well timed.
However, most breeders prefer to stay with the higher standard for safety.
The Role of Semen Extenders and Apps
Semen must be diluted with an extender that protects the sperm during storage and shipping. The ratio depends on the stallion, the extender used, and the target sperm concentration.
Tools like the Botupharma USA app or the Equine-Reproduction.com semen calculator help breeders and vets calculate exact volumes and ratios. These tools reduce human error and improve consistency in breeding results.
When the Vet Says “It Arrived at 30%”
Hearing that semen has only 30% motility sounds alarming, but it may not mean the shipment is poor.
The first step is to make sure the semen is warmed properly before viewing. It should be mixed gently, warmed to body temperature, and examined quickly. If the sample overheats, dries out, or contains too many sperm in one viewing field, the motility will appear much lower than it actually is.
Semen that sits too long in a syringe tip or is warmed incorrectly can appear dead, even when it is not. Some veterinarians have been known to use microwaves or hair dryers to warm samples, which instantly kills the cells.
To confirm accuracy, reputable stallion stations often hold back a sample to check motility 24 and 48 hours after shipping. This allows them to verify whether the semen remained viable in transit.
If the dose was calculated at 1 billion progressively motile sperm before shipping and arrives at 30% motility, that still leaves about 315 million viable cells—enough for good conception chances when timed properly.
Key Takeaways
Low motility percentages alone do not always indicate poor semen quality.
Proper warming, dilution, and timing of insemination make the biggest difference.
More sperm does not always mean better results. Too much semen can cause uterine irritation and lower fertility.
Consistency and accurate evaluation are what truly determine success.
Understanding semen analysis helps you have informed discussions with your vet and your breeding station. It allows you to interpret reports, set realistic expectations, and recognize when an issue lies in handling rather than quality.
In breeding, precision matters more than numbers. Work with qualified reproductive specialists, ask questions, and learn how to read the data that tells the real story.
Credit: This is a summary of the information on this site: Learn Equine Semen Analysis. If you want to do a deep dive, click on the link.
Poll: How confident are you about understanding semen analysis and breeding results?
I rely completely on my vet and rarely question semen reports.
I understand the basics but get lost when percentages are mentioned.
I can follow semen reports if they’re explained in simple terms.
I’ve learned enough to discuss results confidently with my vet.
I could probably explain the difference between total and progressive motility to someone else.
What’s one thing you’d still like clarified about semen evaluation?
Would you like to see more posts along these lines?
Please put your thoughts in the comments below.
Highly informative and easy to understand. I learnt a lot