What a week! I am exhausted just from watching the clinic staff in recent days – Springhill Equine has been in full swing for breeding season these past two weeks! In honor of that, I felt it was time we continued our discussion on horse breeding. This week, I would like to segue into the male side – basics of management of stallions and geldings. A stallion is a male horse that has not been castrated and is sexually mature (vs. a colt, which is not mature). A gelding is a stallion or colt that has been castrated. Sexual maturity is reached at about 4 years of age, but many colts will exhibit stallion-like behavior and sexual activity as early as 8 months of age. They should be separated from females when this is observed.

Castration, or removal of the testes and associated structures, is commonly performed on horses, as stallions can be tricky and difficult to handle and manage. Stallions are often housed in facilities separate from mares so no accidental breedings occur. They must be handled with a firm but cautious hand. With all of this said, there are many stallions out there who are considered docile and easily managed.  Geldings that are castrated before significant stallion behaviors develop, on the other hand, make wonderful companion and riding animals, and are generally more docile. If a stallion is castrated later in life (eg, more than 2 years of age), stallion-like and/or aggressive behaviors may persist post-castration. It is not recommended for the beginner horse-person to own a stallion – usually males are only kept stallions (or ‘intact’) in situations where they will be specifically used for breeding purposes. Some are left intact until physical characteristics develop (eg, larger size, crested neck), and are then castrated. Thoroughbred racehorses are often kept as stallions so they have the potential for a breeding career if their racing career proves successful.

Let’s talk more about the specifics of the male horse reproductive tract. As with any mammal, both stallions and geldings have a penis as their external genitalia. Unlike humans, however, the male horse’s penis at rest is telescoped within itself, and is housed inside the body during the majority of the time. He will externalize the penis (as one would extend a telescope) during times of sexual arousal, for urination, or during sedation/relaxation. There can be medical issues that result in the horse becoming unable to retract the penis, and can become a major problem if left externally for an extended period of time (just like they say on the Viagra commercials – 4 hours is too long!). Tumors and other skin conditions of the penis are relatively common in horses, so regular cleaning of the dirt and skin oils (termed ‘smegma’) from the penis and sheath is important. The vets here at Springhill Equine clean any male horse who is sedated for a dental float, and check them thoroughly for any signs of cancer or other abnormalities.

Stallions also have a pair of testes housed externally in the scrotum. Veterinarians are aware of several conditions that can arise with the scrotum and testes – including infections, tumors, testicular torsions (a medical emergency that presents often as severe and sudden colic), and scrotal hernias. The testes is the assembly factory for sperm, while the next-in-line epididymis is responsible for sperm maturation – eg. packaging and storage. On ejaculation, the sperm leave the tail end of the epididymis, where they are waiting in storage, and travel up toward the pelvis along the ductus deferens (analogous to the vas deferens in humans) until they dump into the urethra (also the exit for the urinary tract) at about the level of the anus. Fluid is added from three different glands (bulbourethral glands, seminal vesicles, and prostate) to help the sperm along their journey. They travel along the urethra through several feet of penile tissue (whose base is just below the anus internally) before exiting with the goal of seeking an egg. In our next blog, we will discuss the various routes a sperm can take to reach that egg – with the stallion actually breeding a mare, or via artificial insemination (A.I.) with fresh, cooled, or frozen semen.

Thanks for stopping by to read my blog this week, maybe next time I could see you in person at the clinic (for some pets)! Keep emailing if you have any specific questions you would like me to cover in my blog (or in the newsletter, for that matter!)! May your litter box be clean, and your food bowl full!

Anyway, we are supposed to be discussing breeding. We have been discussing the many aspects of the cycle of the mare, from seasonality to the hormones involved, the appearance of the uterus and ovaries when the mare is in and out of heat. We will discuss more about the actual breeding in the near future (semen will be covered with the stallion), we are going to assume that your horse has been bred and it is time to look for a pregnancy!

14 day embryo

We typically suggest a pregnancy check at day 14, when the embryo is large enough to be detectable by ultrasound, but when it is in the stage of moving around the uterus. A horse embryo rolls around the uterus for an unknown reason – presumed to be associated with the mare’s recognition of her pregnancy – prior to finding a spot to nestle in. If there is any chance your horse has had a double ovulation, it is critical that your horse be checked between day 14 and 16 post-ovulation. This is the optimal time to reduce twins before the embryo fixes and implants at day 17-18. To reduce a twin pregnancy, the embryo is “pinched” or crushed, with the aim of allowing one of the two twins to survive. This is easiest when they are small and mobile.

This sounds awful, but you must remember that while twin pregnancies do occur and survive to delivery, it is extremely rare to have a pair of twin horses survive to a year of age. A growing foal demands that their placental surface cover all available surfaces of the uterus, so sharing simply isn’t tolerated. Twin pregnancies that aren’t reduced result in one or both foals aborting, or they are born mummified, dead, weak, and/or undersized, and many born alive die soon after birth. If having one healthy foal survive a twin pregnancy is lucky, having a pair is a miracle. The 14-16 day embryo is the best time to manage this condition.

Many older mares have cysts in the lining of their uterus. If we have seen your mare before, we have an idea of where her cysts are located along her ‘Y’ shaped uterus. Cysts and embryos can appear similar sometimes, but the primary difference is that cysts remain the same in size and location, and embryos move and grow. One can imagine a cyst as a peg on a pinball machine, where the ball (embryo) can be delayed, stuck for a moment, or stopped completely if there are a number of them in a group. If there is any question if the structure seen is a cyst or an embryo, a check in hours or days will usually reveal the answer.

Once a single pregnancy is confirmed at 14-18 days, we also recommend checking your mare at 25-30 days. At this time, we look for a heartbeat, which will confirm that the embryo is alive and well. If it is not, we recommend giving the horse prostaglandin to lyse the CL, terminating the pregnancy before the endometrial cups form. Once these structures form, if the pregnancy is lost, the horse will be finished for the season. It will take the rest of the breeding season for the cups to resorb and uterus to return to normal.

Well thanks for stopping by to read my Blog! Until next week, keep up with your own pranks, and stop by to give me some pets! May your litter box be clean and your food bowl full! 🙂

Last week I covered that horses are seasonal breeders during long daylight hours.  Determining when that optimal amount of daylight happens to have our mares cycling is the tough part!  To begin with our Doctors rectally palpate the ovaries and uterus.  Normal ovaries are about half the size of a human fist, getting slightly small when the mare is out of heat and larger when in heat.  During the winter the ovaries shrink down to the size of walnuts.  The uterus on a normal cycling mare varies in tone during an estrous cycle (the period between ovulations).  When your mare is in heat the uterus is very loose and floppy, when she is out of heat it is firm like a well toned muscle.  If a mare is not yet cycling the uterus feels loose and floppy but the ovaries are small.  So palpation is the first clue.

Next an ultrasound machine is used to look at the ovaries and uterus.  Again our Doctors find that mares who are not cycling will have small ovaries with very small (less than 10mm) follicles and a uterus that feels like an in heat uterus but looks like an out of heat uterus (more on the difference later).  If in doubt our Doctors will pull a progesterone level.  A small amount of blood is taken and tested to determine if these levels are low, high or in the middle.  Mares who are not cycling yet will be very, very low.

Now comes the tricky part….Before mares actually ovulate for the first time in a season they build a few big follicles which don’t ovulate, the uterus starts to have tone and everything looks like it is headed in the right direction only to stop just before ovulation occurs.  This can mean several ultrasounds a few weeks apart to determine when your mare is finally ready for breeding!

Dr. Lacher and Dr. King have determined your mare is cycling and we can now work on breeding her.  What the heck does that mean and what are they looking for to determine the perfect time to order semen or send her to the stallion?  Three things have to happen for everything to be perfect: a follicle of 35-38mm in size, a uterus with a hint of edema, and an open cervix.

The ultrasound image below would be what Drs. Lacher and King would be looking for.  They would measure across the black circles to determine when one reaches that magic 35-38mm.

Ovary

Uterus

They will also be looking at the uterus to see if there is any edema present.  Edema is a very normal part of the cycle.  The edema is seen in the image on the right and makes the uterus look like a wagon wheel or orange slice.  Once at least a small amount of edema is present, a follicle of the correct size is seen, and the Doctors palpate an open cervix then an ovulatory timing drug such as deslorelin is given.

Drugs such as deslorelin help us precisely time ovulation.  Once given 90% of mares will ovulate within a 36-48 hour window.  This makes ordering semen from far away, making appointments with stallion owners, and timing of frozen semen insemination much easier.

Next week we will talk even more about the joys of the cycling mare and the fun of breeding!  Until then may your litter box be clean and your food bowl full!

Let me tell you something – for a cat, Easter is heaven. There are all the usual joys of holiday snacking – cookies, delicious cakes, and other goodies flowing in from our wonderful clients. However, instead of having a cold winter day, surrounded by snowmen and the scary horned beasts in nativities, just think about Easter. Small, squeaky chicks, ducks and rabbits on a warm spring day, with many flowers to sniff and soft grass to roll in. And, of course, the always-popular Peeps in the microwave trick. I think it may be my favorite holiday.In celebration of spring (known to us in the Animal Kingdom as the season of the dreaded twitter-painting), I decided to begin a series on breeding your horse. It is a very complicated subject, and very different from what you know about people (or dogs or cats for that matter). In every discussion about equine reproduction, it is important to remember that all individuals are different, and so there can be (and usually are) exceptions to nearly every rule.Every species is unique when it comes to reproduction, and so I’ve learned that we classify many things about it – such if the species is ‘seasonal,’ or only breeds during one part of the year (horses are, cats and people aren’t!). If it is seasonal, when? Horses are considered seasonal breeders, and breed during the time of the year when the days are longest – eg. spring and summer. This is the opposite of say, sheep, who are seasonal but in the fall.  Funnily enough, both end up having babies in the spring (as sheep are pregnant for about 5 months and horses are closer to 11). In Florida, we enjoy a prolonged breeding season due to our ample sunlight, so fall breedings and foalings are not uncommon.

Let’s talk more about seasonality. In winter, the mare generally is considered ‘seasonally anestrus.’ ‘Estrus’ (while many definitions exist) is the term scientists use to describe heat, or the period that the female is receptive to the male. In the horse, it is usually 3-7 days long, with an average of five days. ‘Anestrus’ is the term for when an animal does not experience heat cyclicity. This brings us to another classification for the horse – ‘polyestrus,’ or having multiple heat cycles in one season. All together, the horse is considered seasonally polyestrus (long-day breeder) with a period of winter anestrus. That was your check point – if you don’t understand that statement, please go back to the top of the blog.

Now let’s talk about the transition periods. Horses experience vernal (spring) and autumnal transitions – progressing from the anestrus period to the cyclic period, and back again. Spring transition is a matter of key concern for many people, most notably, the Thoroughbred racing industry. A Universal birth date of January 1^st is assumed for all Thoroughbred racehorses, and so the first baby born in the New Year is the oldest and the strongest in the pack. During these periods, the ovary is slowly adjusting to the new patterns. We will discuss more about ovarian activity and the corresponding changes in the uterus during our next blog, as we will about the specific changes that occur during the transitional periods. As always, thanks for reading! May your litter box ever be clean, and your food bowl full!