Prepare your Mare for Breeding Season

Breeding season is fast-approaching. Here are five tips to prepare your mare—whether she’s a donor, a recipient, or carrying full-term—and ensure she stays healthy.

By Thiago Boechat, With Kaycie Timm

Group of mares walking along fence in pasture
Keeping your mares under lights allows you to regulate their cycles by extending the amount of time they perceive as “daylight.” You’ll want to bring your herd in before dark and keep them in a well-lit area until around 10 p.m., then again starting from about 5 a.m. until full daylight.

The key to a successful breeding season starts with a healthy mare. Whether you have one broodmare or a full-scale operation, these proven tips will help you prepare before it’s time to breed.

Tip 1: Culture your mare to check for infection. Ensuring that your mare starts breeding season on a healthy note begins long before spring. In fact, the best time to start preparing is at the end of the preceding season. 

Before you shut down your mare, culture her to check for infection. If your veterinarian discovers anything that causes concern, treat the infection, then, at the start of the next breeding season, culture her again to ensure that she’s clean before making plans to breed. 

Quick Tip: If you only have one or two mares to breed, it’s likely most convenient to haul them to your vet’s office to be cultured. If you have a barn full of broodmares, schedule an appointment for your vet to come check all your mares at your property at the beginning and end of breeding season.

Tip 2: Use light to regulate your mare’s cycle. You want your mare to foal out as early in the season as possible, so she needs to start cycling close to the beginning of breeding season. Whether you plan to flush your mare or breed her to carry her own foal to term, you’ll need to control the length of time her body perceives as daylight hours. 

The most obvious option to accomplish this goal is to bring her inside before dark and keep her under lights until around 10 p.m. You can use a timer or manually turn the lights back on around 5 a.m., then leave them on until it’s full daylight. Depending on the size of your breeding operation, you can either bring one mare into a stall with lights set on a timer or keep a group of mares in a lighted pen. Both strategies accomplish the same goal of shortening the period of darkness and causing your mare to begin cycling sooner.

Quick Tip: If you don’t have a space to bring your mare(s) inside under lights, you can purchase a mask designed specifically to regulate the amount of light your mare perceives without interrupting her turnout schedule. That way, your mare can stay outside and still get the amount of the light she needs to regulate her cycle. Light-blocking masks can also be helpful with a horse you need to separate before breeding, such as an older mare who can’t stay out with a herd. of broodmares. 

Blaze faced mare with her head through metal stall door
If possible, it’s ideal for your mare to stay near the stallion’s location so the semen is fresh when she’s inseminated.

Tip 3: Provide your mare with the hormones she needs. When you’re preparing to breed a mare, whether she’s a recipient mare, a donor being flushed, or a mare that will carry her own foal, you’ll need to give her hormone supplements. Work with your veterinarian to develop a regimen including hormones to encourage your mare to cycle; hormones to make her ovulate on schedule; and progesterone (or synthetic progesterone) to keep her pregnant, even if it’s only long enough for an embryo to develop. 

Quick Tip: In most cases, it’s helpful to check hormone levels before breeding, then modify your regimen accordingly. For example, if you find your mare’s progesterone level is low, you’ll want to supplement her until at least 100 days after breeding to keep her levels high enough to maintain pregnancy. After that, a healthy diet will keep her hormone levels strong. 

Healthy for the Duration

Once your mare has been successfully inseminated, it’s important to keep her healthy throughout the pregnancy. In addition to key hormones early on, your mare may need vitamin and mineral supplements as she reaches the third quarter of the gestation period. This will help prevent her foal from developing deficiencies or bone problems while still in the womb. About 30 to 45 days before your mare’s foaling date, monitor her closely. When she’s close to foaling, using a foal-alert system can help ensure that you’re on-hand to help when she’s ready to foal. 

Tip 4: Know the semen that you plan to use. While your mare’s preparation plays a major role in the success of the breeding, some stallions have more delicate semen. In that case, you’ll need to inseminate very close to ovulation or consider using deep-horn insemination methods. The best way to ensure success is to have your vet palpate the mare frequently so he knows when she’s about to ovulate.

Quick Tip: You might think a larger semen sample would make it easier for your mare to conceive, but that’s not usually the case. In fact, a low-volume, highly concentrated dose offers the greatest chance for success. That’s because a larger volume often means there’s more semen extender, not more semen. 

Tip 5: Get everyone on the calendar. Coordinate with your veterinarian and the stallion’s owner to schedule insemination with fresh semen at the optimum time in your mare’s cycle. It’s always best to keep your mare near the stallion’s location so the semen is fresh. This prevents any unwanted mishaps if she ovulates sooner or later than anticipated. 

Quick Tip: Remember, even if your mare’s cycle appears normal from the outside, that doesn’t always mean she’s ready to carry a foal. Work with your veterinarian to prevent infection and check for any complications that could hinder her pregnancy before you attempt to breed. 


Thiago Boechat first came to the U.S. from Brazil in 1993. He returned home to attend veterinary school at Universidade Do Oeste Paulista, but returned to the States in 2004. Since then, he’s achieved success at multiple NRHA major events, including the NRHA Futurity and Derby, and currently serves as ranch manager at Silver Spurs Equine–Oklahoma. 

Determine Your Horse’s Bodyweight

Knowing your horse’s bodyweight is an essential management component for determining the best nutrition plan to keep him healthy.

By Dr. Jyme Nichols, Bluebonnet Feeds

Most horse owners and veterinarians underestimate bodyweight when using only visual assessment. A livestock scale is the most accurate method for determining your horse’s weight, but it’s not easily accessible by most horse owners. This poses two questions for horse owners:

  1. Is it really that important to know your horse’s bodyweight?
  2. Without having access to a scale, are there other ways to make an educated estimate of bodyweight?

Here’s what you need to know.

Understanding Bodyweight

Bodyweight is the single most important factor needed for establishing a nutrition program for any horse. Nutrient requirements set forth by the National Research Council are based on bodyweight, therefore you must have at least a general idea of your horse’s bodyweight to determine the appropriate set of nutrient requirements he requires. Bodyweight is correlated with nutrient requirements and total feed intake; larger horses have higher nutritional requirements and must consume more total food than smaller horses.

Understanding bodyweight is also important when it comes to following label guidelines for feed. Many horse owners don’t consult with a nutritionist when choosing a feed program and must rely on the feeding instructions provided by a feed manufacturer. These instructions are required by law to be listed either on the bag or on an attached tag. Each manufacturer may list instructions in a slightly different format, but they’re always based on bodyweight.

For example, one feed tag may instruct to feed 0.5 pound for every 100 pounds of bodyweight. Another may instruct to feed 0.5 percent of bodyweight. For both examples, that would mean feeding 5 pounds per day if your horse weighs 1,000 pounds. However, if you underestimated your horse’s bodyweight, and he actually weighs 1,250 pounds, your horse should have been fed 6.25 pounds per day. If you overestimated bodyweight and your horse actually weighs 800 pounds, he should’ve been fed 4 pounds per day.

In the case of underestimating your horse’s bodyweight and feeding too little, your horse can end up in a negative energy balance, meaning he’ll begin to lose weight and drop in body condition. If you overestimate your horse’s bodyweight and feed too much feed, he’ll begin to accumulate excess fat and become overweight or obese. Both situations can have negative effects on the health and performance of your horse.

Estimating Bodyweight Without a Scale

While a scale is most accurate, it’s not always most practical. Several systems have been established to help you estimate bodyweight.

The most convenient and inexpensive option is a weight tape, which estimates bodyweight based on circumference of the heart girth. However, this is the most inaccurate method. A 2002 study by Ellis and Hollands evaluated the accuracy of four weight tapes on 2,000 horses, including 112 different breed types, and found significant differences among the tapes.

A preferable method for estimating your horse’s bodyweight is the use of calculations that consider both heart girth and length of the horse as shown on page 114. Additionally, consider your horse’s body-condition scoring, neck circumference, and girth-to-height ratio.

The Henneke body-condition scoring system, based on a 1–9 scale, is the gold standard in evaluating body fat. It evaluates specific areas of fat accumulation, seen at right.

Although body-condition score has been an industry standard, it’s a subjective system and isn’t especially useful in differentiating areas of regional adiposity that may be indicative of disease. For example, heavy fat deposits along the crest of the neck are associated with altered metabolic states such as insulin resistance. A standardized 0–5 cresty-neck scale developed by Carter et al. (2009) is a subjective scoring system developed to help assess regional fat deposits that may indicate health concerns.

Girth-to-height ratio (G:H) is another useful tool in assessing proper body condition in horses and is similar to body mass index (BMI) in humans. For this assessment, a measurement of the heart-girth circumference is divided by height. Horses are considered overweight if the G:H ratio is greater than or equal to 1.26 and obese if the ratio is greater than or equal to 1.29. Ponies are considered overweight and obese at G:H ratios greater than or equal to 1.33 and 1.38, respectively.

The Result = Healthy Horses

Horses that are managed at their optimal healthy bodyweight can lead longer, healthier, happier lives and be less likely to suffer from various metabolic diseases and possibly career-ending performance-related injuries.

With tools such as weight tapes, bodyweight calculations, body-condition scoring, cresty-neck scoring, and girth-to-height ratios, even horse owners who don’t have access to a weight scale are capable of maintaining proper bodyweight and condition of their horse.


Dr. Jyme Nichols

Dr. Jyme Nichols grew up on a cattle ranch in the northern Nebraska sandhills. She’s been involved with horses and agricentire life. Dr. Nichols, an ARPAS-certified Professional Animal Scientist (PAS) in the equine discipline, has been presented with research awards from the Equine Science Society and the American Society of Animal Science.

Assisted Reproductive Technologies Allow Your Mare to Show and Breed

Today’s assisted reproductive technologies mean you can show your mare and breed her, too.

By Barb Crabbe, DVM, Photos by Kaycie Timm

Mare and foal graze in pasture
You adore your mare so much, you’ve decided to breed her. But, ideally, you want to continue showing her. Learn the basics of two breeding procedures that let you have your cake and eat it, too.

There’s nothing like a good mare—especially yours. She’s smart, strong, and spins on a dime. It took a while to convince her, but now that she’s decided you’re “the one,” she gives you all she has in every run. If last year’s earnings mean anything at all, you can hardly wait to see what’s coming this year. But, on the other hand, you’d love to breed her so you have a young prospect with all her outstanding qualities.

Enter assisted reproductive technologies—advanced breeding techniques that make it possible to have it all: another stellar year in the show pen and that foal you can point toward futurities! You’ve probably heard about these techniques that allow your mare to produce a foal (or maybe more than one) while she continues to train and compete. In this article, we’ll take a deep dive into how each of these techniques works.

The Basics

To understand how advanced reproductive technologies work, it helps to know a little bit about the early stages of conception and what it takes to create a foal.  

When your mare has a heat cycle, fluid-filled vesicles called follicles develop on her ovaries and grow during the period of estrus. Within each follicle is an egg (called the oocyte).  At the end of estrus, one dominant follicle will typically release an egg, which then passes into the oviduct (a tube connecting the ovary to the uterus). In some situations, there will be multiple dominant follicles, resulting in multiple ovulations. 

For a mare to become pregnant, semen must be deposited into the mare’s uterus very close to the time of ovulation. Individual sperm travel to the tip of the mare’s uterine horn and enter the oviduct where the egg is fertilized. That fertilized egg then remains in the oviduct for five or six days before passing down into the mare’s uterus. 

Once in the uterus, the tiny embryo travels around for approximately 15 to 16 days before implanting itself in the uterine lining. Once settled, the embryo develops and grows. The following requirements must be met for a successful pregnancy to result for a mare. 

  • The mare must produce a viable egg and release it from her ovary. 
  • Viable sperm must be available at the right time and in the right place to fertilize the egg. 
  • The egg/fertilized embryo must successfully pass through the oviduct to reach the uterus. 
  • The uterus must provide a healthy environment for the embryo to successfully implant and grow. 
  • The uterus must provide a healthy environment for the embryo to successfully implant and grow. 
Group of mares and foals stand in pasture
Embryo transfer usually has a 50% breeding success rate, but with an experienced vet and a well-managed recipient herd, that rate can be higher.

For assisted reproductive technologies such as embryo transfer  (ET) or intracytoplasmic sperm injection (ICSI) to be successful, they must accommodate all these steps. Here’s how they work. 

Embryo Transfer

What it is: Embryo transfer means an embryo is taken from one mare and put inside another for gestation and delivery of the foal.  

How it works: During embryo transfer, your mare (the donor mare) is bred just as she would be if she were to carry a pregnancy to term. The breeding will be closely monitored with ultrasound examinations so your vet can determine the exact time of ovulation.  

At the same time your mare is being monitored and bred, the mare that’ll carry her foal (the recipient mare) is also being monitored. For best success, the recipient mare will ovulate one to three days after the donor mare. Because this timing is so important for success, embryo transfer facilities often have large herds of potential recipients, which increases the odds that there will be a suitable mare available to receive an embryo at just the right time. 

On approximately day seven or eight after ovulation, your veterinarian will flush the embryo out of your mare’s uterus by infusing fluid, then recovering that fluid through a special filter that catches the embryo. Your vet will identify the embryo under a microscope and then prepare it to be placed into the uterus of the recipient mare. If you choose to work with an embryo transfer facility with a large recipient herd, the embryo may be shipped to a distant location before being placed in the mare. 

Why choose ET: Embryo transfer provides a way to breed your mare while she continues to train and compete. It’s also possible for your mare to produce multiple foals each year. ET has become quite common, and many veterinarians are comfortable with the procedures of breeding a mare and flushing embryos—making it easily accessible for most horse owners. Success rates for embryo transfer are high. Estimates say you can expect a pregnant recipient mare in approximately 50% of breedings, and with an experienced veterinarian and a well-managed recipient herd that percentage may be much higher.   

In addition, if you’re breeding an older mare or one with poor fertility due to problems with her uterus or cervix that would prevent her from successfully carrying a foal to term, embryo transfer is a good option. 

When using a recipient mare, timing is critical for all phases of the breeding process, from  synching cycles to procuring semen to breeding. These scheduling constraints are inconvenient but can make or break the success of your breeding endeavor.

The downsides: Convenience and scheduling constraints are downsides of ET, particularly if your mare has a heavy training and competition schedule. Time of ovulation can’t be completely controlled—nor can ideal scheduling for the embryo flush. You’ll be at the mercy of your mare’s cycle during those periods. Additionally, she may require sedation or other medications throughout the procedure that can create conflicts with medication rules.   

Finally, embryo transfer will only be successful if you mare’s reproductive function is normal regarding ovulation and movement through the oviduct following fertilization.

This is typically less of a problem for a young, healthy performance mare, but can create challenges for an older mare or a mare with fertility issues that involve more than just the uterus. And if you are breeding to a subfertile stallion or one with limited semen available, successful embryo transfer does require a full dose of good quality semen. 

Intracytoplasmic Sperm Injection 

What it is: During ICSI, an egg is harvested from your mare, inseminated in a laboratory, and implanted in another mare for gestation and delivery of a foal. 


Contemplating embryo transfer or ICSI is a bit like dining in a five-star restaurant. When it comes to cost, if you have to ask, you probably can’t afford it. Although costs vary depending on your geographical location, accessibility of facilities, and available expertise, expect to spend anywhere from $4,000 to $7,000 for an embryo transfer and $8,000 to $12,000 for ICSI. And there’s no guarantee the procedure will be successful. It’s always possible you’ll pay the bill and end up without a foal to show for it.

How it works: The first step for ICSI is aspiration of the oocytes from your mare’s ovaries, which is performed with an ultrasound-guided needle inserted through her vaginal wall and into individual follicles.  Oocytes can be collected from either dominant, mature follicles near the time of ovulation or from immature follicles. 

In the early stages of development of these techniques, collection of dominant follicles was more popular—primarily because mature oocytes are easier to aspirate and have a higher rate of developing into a viable embryo. Once harvested, mature oocytes are much more sensitive than immature oocytes, making successful transport much more complicated.  

Collection of immature oocytes is much less time-sensitive, and multiple eggs are commonly collected at the same time. On average, six to eight eggs can be collected as often as every 14 days. Although the success rate with each individual oocyte may not be as high for immature versus mature oocytes, the larger numbers collected mean overall success in establishing a pregnancy is just as good, if not better.  This, combined with the scheduling convenience and improved technical skills of practitioners performing the aspirations, has resulted in a
gradual shift toward ICSI using immature oocytes as a more common procedure. 

If collection doesn’t occur at a facility with an ICSI laboratory, the oocytes will be transported to an ICSI facility where they’ll be fertilized using  microinjection of a single sperm cell, then held for six to eight days. If the fertilized egg successfully develops into an embryo, it’ll then be transferred into a recipient mare’s uterus for gestation. 

Breeding laboratory door
When using a recipient mare, timing is critical for all phases of the breeding process, from  synching cycles to procuring semen to breeding. These scheduling constraints are inconvenient but can make or break the success of your breeding endeavor.

Why choose ICSI: Like embryo transfer, ICSI provides a way that you can breed your mare while she continues to train and compete and also allows her to produce multiple foals each year. Success rates are good,  but depend on a number of different variables, including the number of oocytes that can be collected with each attempt and the skill of the practitioner. If your mare has a heavy training and competition schedule, pursuing a pregnancy via ICSI will disrupt this schedule less than breeding via embryo transfer.  

Finally, if your mare has fertility issues that include abnormal cycles/failure to ovulate, a blocked oviduct, or an unhealthy uterine environment, she can still produce a foal as long as she has healthy oocytes available for collection.
If you hope to breed to a subfertile stallion or one with limited semen availability, ICSI has a much lower requirement for sperm than
embryo transfer. 

The downsides: Although ICSI is becoming more prevalent, fewer practitioners are comfortable with oocyte aspiration techniques compared with embryo transfer, and availability of ICSI laboratories capable of performing the sperm injections is still limited. As expertise becomes more widespread, however, the breeding industry is headed in this direction. If you plan to breed your performance mare, ICSI is clearly something to consider.


If you have a top-notch mare, there’s a good chance you’ve thought about retiring her as a broodmare when her performance days are done.  If you’d like her to carry her own foals, it’s important to plan ahead. Older maiden mares (even those that have had an embryo-transfer or ICSI foal) can present some reproductive challenges. If your mare has never carried her own foal to term, there’s a greater chance her cervix will fail to relax normally during her estrus cycle. She’s likely to retain fluid in her uterus after breeding, which can increase the risk of inflammation (known as breeding-induced endometritis) or even infection that’ll reduce the chances she’ll get pregnant.  To minimize this risk, it’s best if your mare can carry a foal to term before she’s 10 years old. If the futurities and early derbies aren’t part of your plan, some experts believe it’s reasonable to breed your mare as a 2-year-old before intense training begins. For others, taking a year off as a 7- or 8-year-old would be something to consider. 


Dr. Barb Crabbe is a graduate of UC Davis School of Veterinary Medicine and completed an internship in large animal medicine and surgery at Washington State University. Crabbe is a private equine practitioner and owner of Pacific Crest Sporthorse in Oregon City, Oregon. She’d like to thank Ryan Ferris DVM, MS, Dipl. ACT of Summit Equine in Newberg, Oregon, for assistance with preparation of this article.