Precious Cargo - Breeding with shipped semen, cooled or frozen
by Christine Hamilton

It has happened to many of us - you’ve been showing and competing with your mare when suddenly you get an urge to hear the patter of little hooves. Why not? It will expand your horse experience that’s for sure. Nothing trains an equestrian like an independent-minded little one. With today’s advancements in the world of shipped semen, frozen or cooled, you can choose from stallions across North America or even the Atlantic, without your mare leaving the home barn.

There are, however, easy mistakes to make. Just as every novice learns to double-check that girth, there are some basics every horse person should know before they enter the breeding arena.

Horse Sport sat down with veterinarian Dr. Racquel Rodeheaver of Equine Field Services at Colorado State University’s Vet Teaching Hospital to see what advice she gives to clients breeding their mare for the first time. Rodeheaver’s extensive experience in equine reproduction includes time spent at the well-respected practices of Rood & Riddle in Kentucky and Littleton Large Animal Clinic in Colorado. She also worked at CSU’s renowned Equine Reproduction Laboratory before running her own private ambulatory practice.

She’s had a lot of experience helping owners get their mares in foal.

Breeding Soundness Exam
Before you consider breeding your mare you should have a thorough breeding soundness exam performed on her. Rodeheaver explained, “[A breeding soundness exam] entails a very thorough physical exam and a reproductive exam, which would involve evaluating her conformation reproductively and doing a rectal palpation and ultrasound”. The ultrasound will give the veterinarian a quick view of the mare’s uterus and ovaries, checking for uterine cysts and fluid and for ovarian activity.

“Then we would do a vaginal exam, a cervical palpation and exam and a uterine culture. A culture allows us to test for any type of bacterial or fungal infection involving the uterus. We call that endometritis.

“Finally, we would do a uterine biopsy. We take a small sample of tissue in order to determine if there is any inflammatory condition in the uterus or any kind of aging changes or fibrosis that might limit the pregnancy.

“The goals are to really look at the mare’s reproductive health so that we can come up with a prognosis, or a level of expectation of what our chances are of getting her bred.”

The exam will help you get an overall idea of your mare’s reproductive health and catch potential problems early, such as a predisposition to uterine infection. It also helps you decide how best to manage your mare.

Rodeheaver explained, “I serve clients on an ambulatory basis. I also have the luxury of having a [clinic] facility available. For a mare that doesn’t have any reproductive problems, I will manage her [at home] on the farm. If we need to manage her more intensively, say we have to treat her uterus with antibiotics, lavages, [etc.] most often I will encourage you to bring the mare into the facility”.

Before the Breeding Season Begins
There are several other things to consider before you start breeding your mare. First and foremost is nutrition.

According to Rodeheaver, “If a mare does not have adequate nutrition levels, then her reproductive performance is going to be affected. For most broodmares, I like to be able to feel their ribs but not see them; and that would be a body condition scale of five to six”, on a scale of 1-9. A mare’s nutritional requirement changes when she moves from a performance career to the breeding shed. Your veterinarian can help you set up a feeding program.

Rodeheaver continued, “It becomes critical with a pregnant mare in the last four months of pregnancy because that’s when the developing fetus has its most rapid bone growth. Nutrition is an important aspect of trying to prevent some of the developmental bone disorders that can happen [in newborn foals]”.

Another thing to consider is the stallion, of course. Selecting the stallion involves more than pedigree and/or conformational compatibility with your mare. You must also consider what the stallion manager/owner’s fees are, whether or not the stallion will ship semen and whether or not he offers frozen or cooled-shipped semen.

Early in the Breeding Season
Once you’ve picked your stallion you need to pick the time you want to start breeding. With cooled-shipped semen when you breed is dependent on the stallion’s availability. He may have a set collection schedule (Monday, Wednesday and Friday only) or he may only be available for a certain number of months due to a show schedule.

Your target breeding time also depends on when you want to breed. Rodeheaver said, “If we are not trying to target a breeding date in February, then a lot of horse owners have no problem breeding their mares during the natural breeding cycle”, in May, June, July.

She pointed out that in a number of cases “there are clients that want foals born as close to January first as possible. In those situations we want to try to accelerate a mare through the transitional period”.

“In the winter, [mares] stop cycling; and there are a lot of hormonal and endocrine mechanisms that shut down over the winter months. When a mare starts to think about breeding season again, she enters a time when she is hormonally priming the pump. When a mare is priming her reproductive pump, breeders say ‘she’s in transition,’ or ‘she’s in her transitional cycle’.

“The biggest factor that triggers a mare into the transitional cycle is increasing daylight hours. The eye senses the increase in day length and the ovaries start developing follicles where eggs will eventually mature. In late transition, a mare will begin developing large, dominant follicles.” Eventually, one will ovulate, releasing an egg.

“[The mare’s] first ovulation is fertile, but a lot of times it’s a headache to predict. A mare in late transition may grow a dominant follicle, then it may regress and she’ll start to grow another one that may do the same thing,” without ever ovulating.

“It’s especially difficult when trying to time an ovulation with a shipped semen order. When breeding with cooled or frozen semen, I recommend documenting the first ovulation of the year [without breeding on it], then making plans from there.”

Once a mare has shown her first ovulation, she has entered her breeding season and should cycle regularly.

When left to nature, a mare will come into the transitional period as the daylight hours lengthen. You can bring her into it earlier with artificial lighting. Rodeheaver advised, “It takes advance planning. You need to have a mare under lights for 60 days prior to your target breeding date”. So, if you want to begin breeding in February, you start her under lights in December.

Rodeheaver explained, “You need to have the mare in a stall where you [have enough light to] read a newspaper in any corner of the stall. Make sure that she is not able to get her head outside the stall door to avoid the light”.

“You want to increase day-length to 16 to 18 hours, so keep her under lights until 10:00 or 11:00 at night. Be sure to turn the lights off, the mare has to have a night period.”

Breeding the Mare
Rodeheaver looks at “breeding through a couple of different avenues. When you’re dealing with fresh semen, the viability and longevity of the semen is longer, therefore, your time of breeding and your time to ovulation can be a broader window. Usually you want your time of ovulation to be within 48 hours of your time of breeding with fresh semen”.

“With cooled-shipped semen you have to narrow down that window. You want your time of breeding to be within 24 hours, prior to ovulation. With frozen semen, it’s even narrower. So, because that window becomes narrower, and we have to time insemination so closely to ovulation, it requires more intensive management of the mare.

“A normal cycling mare has a three-week cycle: two weeks they’re out of heat, one week they’re in heat. When [the client] sees that mare come into heat, that’s when we want to check her [via ultrasound] to monitor the developing follicle.

“I check the mare initially every other day and then at least every day as we get nearer to the time of breeding.”

With cooled-shipped semen Rodeheaver wants to give a stallion manager “at least 36 to 24 hours notice” before ordering. She continued, “When I establish that there is a dominant follicle that is maturing normally along with signs of [heat], I’ll go ahead and order semen”. With frozen semen, the breeding doses are already on hand.

To help better predict the ovulation, veterinarians can use different hormones that will cause a dominant follicle to ovulate.

Rodeheaver explained, “There are two different ways to induce ovulation. One is called human chorionic gonadotropin (HCG); it’s an intravenous injection. HCG will induce ovulation within about 36 hours”.

“The second agent is GnRH, gonadotropin releasing hormone. We call that Ovuplant. That is an implant that is given subcutaneously in mares. That will induce ovulation within about 40 hours.

“There’re advantages and disadvantages to both. HCG is less expensive. It can also be less effective if it’s given multiple times throughout a mare’s breeding history. Sometimes it is less reliable as to the exact timing of ovulation.

“Ovuplant is more expensive. It has a more precise timing of ovulation once it’s given. The standard practice right now is to administer it and then once the mare has ovulated, to remove the pellet you implanted. There has been history of mares not coming back in to cycle normally”, if the pellet is left under her skin to dissolve on its own.

With cooled-shipped semen, Rodeheaver arranges “a time to inseminate the mare based on what the expected delivery time is of the shipment”. If a mare is at her clinic to be bred with frozen semen, she thaws the straws and breeds the mare there.

She continues to monitor the mare via ultrasound to verify when she ovulates. If the mare doesn’t ovulate as expected, Rodeheaver will breed her again, reordering cooled-shipped semen or thawing another dose.

Evaluating the Semen
Sometimes evaluating the semen you receive is “limited on an ambulatory basis. Not all practitioners have a microscope that they can take into the field with them”. It’s another advantage of having the mare at a facility where that equipment is readily available.

Rodeheaver stressed that, “if you’ve gone into a second breeding situation and you don’t know what semen quality is it’s important to get it evaluated”.

Semen is usually evaluated based on its motility, or how well the sperm cells are moving. In most cases, the higher its motility, the higher its fertility. However, Rodeheaver pointed out that often with cooled-shipped or frozen semen, “motility does not always equal fertility”. Stallions vary greatly as to how their semen responds to the cooling or freezing process. Semen with good motility may not be fertile and vice versa.

For that reason, even in cases where the semen motility appears poor, Rodeheaver recommends going ahead and breeding the mare. She doesn’t question semen fertility until she’s in a second or third breeding cycle and she can’t attribute the reason why a mare is not in foal to anything else.

Final Comments
In any shipped semen situation, Rodeheaver stressed the importance of being “in good communication with the stallion manager”, especially in the case of cooled-shipped semen. “This is a team effort.”

The long-distance aspect of a shipped semen situation can make things frustrating, especially if a mare is not getting in foal. Rodeheaver added, “All of us have the goal of getting the mare bred. If we can all focus on that goal, then communication is clear, respectful and cooperative in working toward that effort”.

And, by the way, “Don’t forget to have your mare checked at 14 days for a pregnancy! It’s the best time to take care of a twin situation, if necessary, and if she’s open [not in foal], she should be coming back into heat ready to go again”.

There are advantages and disadvantages to both cooled-shipped semen and frozen semen. Cooled-shipped semen is typically collected and shipped via overnight delivery for breeding the next day. With cooled-shipped semen, you want to breed the mare within 24 hours prior to the time she ovulates (releases an egg). So, the semen must be ordered timed to when the veterinarian thinks the mare will ovulate. In addition, cooled-shipped semen does not keep very long. Few vets will use cooled-shipped semen that is over 48 hours old because of the risk of bacterial growth in the semen.

The advantage is that cooled-shipped semen has a typically higher fertility. The disadvantage is that it must be ordered as needed and it will not keep.

With frozen semen several breeding doses can be sent at one time for a veterinarian to have on hand as needed. However, because fertility rates are typically lower, most veterinarians feel that frozen semen should be bred within 12 hours prior to ovulation. Veterinarians will often ultrasound a mare twice a day or more in order to time the breeding just right.

Frozen semen also requires more expertise in the way it is handled and the equipment it requires. Techniques for freezing vary greatly and each frozen semen shipment should come with detailed instructions as to how many straws make one breeding dose and exactly how it should be thawed. Breeding facilities should have liquid Nitrogen holding tanks, water baths for thawing, etc.

The advantage is that frozen semen is immediately on hand for the veterinarian’s use. The disadvantage can be a reduced fertility and greater management requirements.
Rodeheaver often manages mares with cooled-shipped semen at their home barns. With frozen semen, she said, “It just makes more sense to have the mare at a facility, because I like to [ultrasound] her more often”. The frozen semen can also be kept in a facility’s liquid Nitrogen tank. “Can it be done at the farm?” she said, “Absolutely. My recommendation is for the mare to come to the facility.”

Watch out for these mistakes when receiving shipped semen!
• Double-check the shipping address!
• Know when a shipper is supposed to arrive!
• Be able to track the package!
• Don’t leave shippers in extreme heat or extreme cold!
• Don’t open the shipper. Let your veterinarian handle
the semen!

What are some things I need to know before I sign a contract?
Who is going to breed your mare—select an ambulatory veterinarian with equine reproductive experience or a local breeding facility? Make sure the veterinarian uses an ultrasound.

The fees involved and when they are paid—know the charges for collections and/or breeding doses, shipping charges, stallion service fees and shipping container deposits.

Shipping availability — with cooled semen, verify that you have overnight delivery service or that the semen can get to your regional airport.

Semen availability — with cooled semen, know the collection schedule. With frozen semen, know how many breeding doses are sent with each shipment.

Return policies and Live Foal Guarantees - know what happens when your mare does not get in foal.

Horse Sport March, 2003