Page 24 - January 2007 The Game

24 The Game, January 2007 Canada’s Thoroughbred Racing Newspaper
THE ROLE OF PROGESTERONE
Equine Health
This pivotal hormone can make or break a pregnancy.
by Karen Briggs
For the first two weeks of a mare’s pregnancy, the hormones produced are the same as those she normally has when she is 'open' and in diestrus (out of season). But that all changes around Day 14. In an open mare, the hormone called prostaglandin destroys the corpus luteum (formed from the tissues of the burst ovarian follicle, after ovulation) at that time ... while in a pregnant mare, the corpus luteum persists and continues to secrete progesterone, the hormone which prevents the mare from coming back into heat, tightens the seal of the cervix (the entrance to the uterus) to prevent infection, and causes the uterus to become increasingly vascular (blood-engorged) to help nourish the unborn foal.
Horses are fairly unique in terms of how progesterone continues to be secreted to maintain the pregnancy. In the base of the pregnant horn of the mare's uterus, distinctive, irregularly-shaped areas develop in a ring configuration. These are called the "endometrial cups", and they secrete a special hormone called equine chorionic gonadotropin (eCG), detectable in the bloodstream by about Day 35 of the pregnancy (and sometimes persisting till about Day 150). Only a
few other species are known to use this mechanism, including elephants and rhesus monkeys.
eCG's role is to maintain and develop the corpus luteum beyond Day 35, and even trigger further corpus lutea to develop. Meanwhile, progesterone secreted by those corpus lutea ensures that the mare doesn't come back into heat. By somewhere between Day 70 and 100 of the pregnancy, the endometrial cups start to shrink in size, and eventually detach from the uterine wall and slough off, allowing the placenta to take over the job of progesterone secretion.
After the fourth or fifth month, progesterone levels gradually decline, till they reach a low of about two nanograms per millilitre by about Day 180 of the pregnancy. By that time, though, the pregnancy is well-established and able to continue to sustain itself without so much hormonal support.
Progesterone surges once again just prior to foaling, to stimulate the development of the milk-producing glands of the mare's udder.
Progesterone is critical for the maintenance of an equine pregnancy, especially in the beginning stages. A
deficiency of this hormone
may be responsible for many
cases of early embryonic
death or abortion. In theory, since the mare's system of progesterone production is more complex than in most species, there's more opportunity for something to go wrong. But why would a mare have a progesterone deficiency?
The most likely explanation would be a malfunction of the corpus luteum (or lutea) -- for example, the secondary CLs may fail to develop sufficiently between Day 40 and 60 to take over progesterone production, or the primary luteal cells might cease progesterone production pre- maturely, before the endometrial cups can get the secondary system up and running. Abortions at the fourth or fifth month stage are often blamed on the placenta secreting insufficient progesterone. It's also possible that the secondary CLs sometimes send out contradictory signals by secreting estrogen (stimulating estrus) rather than progesterone ö about one in five pregnant mares will show signs of behavioural estrus (responding to a stallion), indicating that this biological glitch may be quite common.
Because progesterone levels are so
crucial to a healthy pregnancy, many veterinarians recommend the administration of extra progesterone, in the form of the drug altrenogest (Regu-Mate), as a preventative measure for mares who are suspected of being difficult to keep in foal. This therapy is something of a matter of debate, with some practitioners considering it a wise precaution, and others seeing it as of questionable benefit.
Regu-Mate is generally administered for the first third of the pregnancy, by squirting 10 cc daily in the mare's mouth. After the first three to four months, the mare can be gradually weaned off it, though some veterinarians recommend continuing the daily dose through almost the entire gestation if she has a history of aborting. Regu-Mate is expensive, and administering it is inconvenient (it requires wearing gloves, and some mares are less than cooperative about their daily dose). But on the up side, the drug has no notable side-effects on either mare or foal, nor should it affect the mare's future fertility.
Dave Landry Photo
The Course of a Lifetime
My first year of racing, 1973, was a year of exponential growth. At a time when very few women were race riding, I had earned a valid jockey’s licence. I had won my first race, or, in racetrack lingo, broken my maiden. I was apprentice for B&V stables and I now had the respect of most of the jockeys at Suffolk Downs in Boston. Every race was like a full college course compressed into a short series of heart stopping moments—every move I made resulted in instant suc- cess or near disaster. When I’d ridden jumpers, I could repeat the same mistake without dire consequence, but in the middle of a pack of thundering thoroughbreds, one mistake could cost me my life.
I’d made many of the usual apprentice errors. One time I was weaving my way through the pack to get into a huge opening right behind the front runners. I drove my horse through, ready to challenge the leaders. The moment I galloped into the opening I saw why it was empty—a bandage was unravelling from the hind leg of one of the leaders, a lethal ribbon streaming out behind him. I snatched my horse up just as he was about to step on the bandage and flip over. Lesson learned: jockeys do not leave huge, gaping holes in the middle of the pack without good reason.
At 40 mph, a horse will move as much as two feet laterally when changing leads. In one unforgettable race, I watched a young jockey in front of me dash for the opening on the inside rail going into the clubhouse turn. Just as his horse began to squeeze in, the horse in front switched leads and closed the opening. Though I was several lengths back, the terrifying sound of heels on heels reached my ears. The young jockey’s horse stumbled but managed to right himself and stay on his feet. It was a lesson neither of us would forget.
My education continued one morning when a train- er approached me with a rather unusual request. He had a sponsor who wanted to see his horse break on top.
Suburban Squire, a four year old gelding, had never shown speed and the trainer asked me if I thought I could get him in front. After my first gallop on the horse I asked for two weeks to re-school him. Exactly 14 days later, Suburban Squire and I broke from the gate and went to the lead. I nursed him around in the three- quarter of a mile race and finished third in a photo.
My reward was another horse from the same stable, a five year old stallion named Cabtrail, who would prove to be the greatest challenge yet. Woe to any rider, apprentice or journeyman, who didn’t follow Cabtrail’s rules. When beginning the morning exercise, the colt would gallop along with his head turned sideways, first peering at the infield and then swivelling around to watch the horses on the outside rail. When he was ready, he would straighten his head and only then was I allowed to take a light hold of the bit. In a race, I had to break without touching Cabtrail’s mouth and let him get into gear before taking a hold. If I did this, he would break straight. If I took a hold, it was anyone’s guess which direction he would go in.
A jockey who threw a horse’s head away coming out of the gate would be heavily penalized by the stewards if that horse changed paths and bumped another horse. I knew I’d never be able to convince the stewards that this horse would only change paths if I did take a hold. I put my acting ability to good use to make it look like I was steering the horse without actually touching the bit. Later that year, I was not available to ride Cabtrail in a race. The jockey didn’t follow instructions and Cabtrail veered into the outside horse, stumbled and unseated his jockey.
After this incident, the trainer hired me as his sole jockey. My education continued with more unusual horses to ride. Suburban Squire, the only uncomplicat- ed horse, was now allowed to run his preferred style from off the pace. Another gelding, who I remember
only as Big Red, had front ankles that looked like two bags of marbles. Red would start off stiffly, but when he gave a little toss of his head, I knew he was ready to go. Well meaning friends advised me not to ride him, but Red was a wise old campaigner who taught me many lessons. He knew instinctively when a hole would stay open and when it wouldn’t, giving me a more confident sense for judging the situation.
Soon other trainers were offering me their sore or totally neurotic horses. I drew the line when it came to unsoundness but, at least once, I would try out the eccentrics. One horse
A Head at the Wire
The tenth in a series of real life stories by Paddy Head majeek05@hotmail.com
had suddenly decided not to break from the gate and I was hired to find out why. I spent two hours in the starting gate one morning while other horses came and went, breaking beside me. Eventually we had to be backed out. My conclusion was that the horse must have a good reason for not wanting to run anymore. I don’t know what method was finally used to persuade this horse to break from the gate but in his next race, he broke his leg and was destroyed.
Jockey Paddy Head weighing out
Like any first year student, I was learning my lessons, some with a smile, some with tears, but I didn’t regret a moment of my education.