• James E Aarons DVM

Palpating the Ovaries: Fear of Failure, Chapter 33


Once Tina identified a horse as coming into estrus she arranged a pre-breeding exam. The breeding shed is a two-room affair: the lab, and the horse room. Obviously, the horse space is the largest; there is a metal pipe cage with swinging doors where the mare stands comfortable and accessible to procedures. And in the other corner is a dummy mare set in a permanent receptive pose, basically a barrel attached to a pole, with gimmicks and pretties attached. And to enhance the ambiance, the entire shed is paneled in knotty pine wood.


Anyway, Tina would find a mare in heat and call me to perform a uterine culture, cytology, and biopsy. If all those tests came back normal, we'd short-cycle her the middle of her next cycle, setting her in line for AI, artificial insemination.

If any results came back abnormal I worked to resolve the problem. Usually, it was an infection in the uterus.

While I'm inside reviewing Tina's paperwork regarding the mare's cycling history, she's in the breeding area getting the mare ready for me. The horse is caught up in the metal cage; we call it the stocks, held by a handler at her head grabbing the lead rope. Usually, we only needed one handler, but two were helpful in midseason.

Tina wrapped the tail with a six-inch long roll of brown gauze, unrolling the material starting at the place where the tail starts, to prevent hairs from getting in the way of our examining. I was readying for the rectal palpation, pulling a long plastic sleeve up to my right armpit, dribbling copious amounts of lube onto and around my hand and wrist, readying to plummet into the mare's rear, her rectum, the top hole. Smearing the lube on her anal sphincter, and holding my fingers in a teepee formation I pushed in, inching forward searching for feces. The poop had to come out before I could work myself in. Once the rectum was evacuated I pushed back in and began a methodical review of the mare's organs, feeling the tone of the cervix and uterus as well as the activity of the ovaries, i.e. whether or not they had follicles, these bubbles I could feel meant she was cycling.

Two places to explore: Rectum or Vagina:

The rectum allows me to push my hand above the vagina, the cervix, the uterus, all the way to the ovaries.

Next I drop down to the vulva, after cleaning up of course, and check the vagina and the cervix by looking at it through a speculum.

That was the prep work, the rectal palpation. I palpate everyone in heat a few times throughout the month to get a feel for where the gal is in her yearly, then monthly cycle. Tina and I do this for the entire herd each year. The mares that still have babies suckling require an extra handler; even these new moms are assessed for the next AI reception.

Today we were doing a pre-breed workup on a mare in burning heat. That's why she was stamping her feet,and the handler always yelling at her, yanking her chain.

Tina smiled refocusing on tidying the rear up for the vaginal probe by scrubbing the vulvar area more than a few times, making sure to get goobers out of cracks and crevices because cleanliness is good.

My turn came when Tina could no longer see any dirt on a newly wetted handful of moistened cotton; she nodded and allowed me to take over.

I unsheathed a vaginal speculum, a twelve-inch long reflective cardboard tube. That and a flashlight allowed me to see into the vagina, the first abyss behind the vulvar lips. Pointing the flashlight beam along the long silver tube, I pushed the speculum straight forward and a little down looking for the cervix, it was the primary structure in the vagina, looking like a round mound of tissue with a hollow center, the os, or opening into the uterus. This mare's cervix was floppy and flaccid, leaning downward as if it were tired, or hiding the os from the penis maybe, in a kind of hormonal pre-tease? I scanned the walls of the vagina looking for abnormal bumps or redness, especially checking the vaginal floor for signs of irritation suggesting urine pooling. Everything looked good; I was ready to push into the cervix, first with a swab I guided into the uterus through a protective tube to keep it from getting contaminated from the outside. The swab was then rolled onto a blood agar plate and then a glass slide to give me a culture and cytology. If no bacteria grew on the blood agar in three days in the incubator the mare was clean. Cytology would also bear this out, showing only normal vaginal epithelial cells, not white cells suggestive of inflammation and infection. Finally, I penetrated the cervix a final time pushing a two-foot long uterine biopsy forceps having large jaws to dig into the uterus, chopping off a piece of tissue for histopathology; this is the final of the three tests. The small tissue sample is dropped into formalin and sent to the laboratory for histopathology.

After all these results are in Tina and I will let the clean mare go for ten days, then short cycle her with a prostaglandin injection to get her into the breeding lineup ASAP. Tina was set to inseminate her when I told her it was time. Now we needed to chart the growth of the follicle on the ovary until it burst open, freeing a mature egg to mate with sperm that we were ready to drop in at the perfect moment.

Here is a diagram of an equine ovary with follicles at different stages of maturity, starting with the Primary Follicle, #1 and ending with ovulation after the Graafian Follicle (#4) bursts open freeing the egg.

This is a cool series of ultrasound scans that shows a developing follicle almost past the 40mm stage. The second shot is a day later just before ovulation. You see the thin tissue lining the follicle? That secretes estrogen, and when ovulation occurs the follicle will fill in with blood and begin to remodel into the corpus lutea, the tissue that secretes progesterone. Now the body readies for an embryo implant, preparing for a long term pregnancy.

Using my black and white ultrasound to image the ovaries I look for enlarging black spots growing from the whiteness of the ovarian tissue. These dark regions are called follicles, and each follicle contains one egg. The follicle is growing in blackness because the follicular fluid surrounding the activating egg is increasing, continuing to fill with fluid until it ruptures, usually when the follicle enlarges to 45 mm, about the size of four fingers. The rupture is termed ovulation. Breeding starts when the egg is released, traveling from the ovary into the oviduct of the uterus. Sperm have more than sufficient stamina and will power to swim across the entire uterine body, picking a horn to swim up, some meet the egg as it drops into the fingers on the oviduct. These fimbriae gather the ovulated egg towards them, pushing it into the oviduct, so the baby grows inside the uterus and not ectopically.

Last Chapter: Equine Repro Man Next Chapter: Breeding Shed


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