welcome to this lecture on the basics of stud farm...

Welcome to this lecture on the basics of stud farm practice. The basics we are referring to are the “bread and butter” procedures that a veterinarian contends with on a daily basis at a stud farm.

Due to the advent of ultrasonography, teasing is less important than it used to be. However it is still quite important. In fact there are some instances when one simply has to tease a mare to ascertain if she is where we think she is, in her estrous cycle. Perhaps more importantly, sometimes one has to determine if a mare is in “psychological” estrus as well as “physiological” estrus. This is absolutely essential in Thoroughbred practice where all breeding is “natural” as opposed to breeding that is done by artificial insemination (AI). Mares cannot be teased efficiently in large groups because many mares will hang back, away from the stallion, even if they are in estrus. This is especially the case if mares in a paddock are teased across the fence. Perhaps 20 or 30% of mares in estrus will not come forward and display receptive behavior to the stallion. The most efficient way to tease a mare is to restrict her movement in a set of teasing stocks and to let the stallion come into close contact with her.

In this case a mare is being used as a so-called "live mount" for semen collection. First, she's teased to see if she will remain motionless and will not kick the stallion. If she is in diestrus she will kick or strike out with her front legs. Even though a mare might be in good standing estrus, it is wise to apply a twitch and sometimes to lift one of the fore limbs as the stallion approaches. This is because some mares are frightened at the approach of the stallion. At stud farms where artificial insemination is used exclusively, "live mounts" are seldom used. Instead, a dummy or "phantom mare" is used to collect semen. This is shown in the two images on the right-hand side. Semen collection is far easier and safer when using a phantom mare. That is probably why the individual at top right has a big smile on his face!

When one is using only artificial insemination, it is seldom necessary to tease mares because ultrasonography gives us so much information as to the status of the reproductive system. In this photograph, the ultrasound image at top left shows that the uterus is under the effect of estrogens, giving it the remarkable edema pattern (arrow) seen here. This is due to the presence of the large follicle in the ovaries, this one being about 4 cm in diameter. After a follicle has reached a diameter of perhaps 3.5 cm, one can expect ovulation at any time. The orange arrow at lower right points to a corpus luteum where an ovulation has. Incidentally, it is impossible to say how old this CL is. The follicle adjacent to it has yet to ovulate.

Sometimes it is helpful to be able to regulate the time of ovulation in a mare. Mares may languish at stud farms for very long periods of time, incurring substantial board fees and being exposed to the risk of infectious diseases. Therefore one wants to leave a mare at a stud farm for as short a period as possible. This can be done using a combination of hormones known colloquially as P&E. In essence, progesterone and estradiol given intramuscularly for 10 days, during which time the estradiol component causes suppression of FSH Secretion, regression of follicle development and prevents further follicle growth. The progesterone only serves to keep the mare out of estrus during this time. A prostaglandin injection is given at the end of treatment to ensure that there is no luteal tissue present when treatment stops. A new follicle waves starts immediately after treatment stops and after about eight days, a pre-ovulatory follicle is present. To ensure that ovulation occurs as predictably as possible, an injection of hCG is given on the morning of the eighth day. This causes ovulation to occur with a great predictability about 1 ½ days later i.e. on day 9.5 after the end of P&E. treatment. P&E is also used commonly to synchronize the time of ovulation with shipments of cooled semen or to control ovulation closely, so that repetition of insemination with frozen-thawed semen is kept to a minimum. It is also used for synchronizing the estrus cycles of mares for embryo transfer (ET).

To ensure that ovulation occurs as close to the desired time as possible one usually tries to mimic the endogenous surge of LH that occurs during estrus. If you revisit your basic physiology, you will be reminded that the LH surge in mares is particularly long, about to 5 days or more, usually peaking about one day before the end of estrus. This means that any hormone that is used to mimic that surge must also have a long acting effect. Native GnRH i.e. the natural hormone is not able to elicit a long lasting surge such as this unless it is given using special treatment methods, beyond the scope of this discussion. Therefore potent, long-lasting analogs of GnRH are used. The analog that has been developed for this purpose is deslorelin, sold under the trade name “Ovuplant”. Ovuplant is given in the form of an implant subcutaneously adjacent to the vulva lips or in the neck region. It should be removed after 48 hours, not left in situ. If it is not removed, deslorelin will start to have a suppressive effect on the release of gonadotropins, causing a delay in the onset of the next estrus period; an effect that is used as a contraceptive in other animals. This effect is true of all stripes of GnRH, native or analog. Ovuplant is a highly effective and safe product, widely used on stud farms. An injection of hCG, often used under the trade name “Chorulon” is also a highly effective hormone for inducing ovulation. It is a complex glycoprotein molecule that is slowly broken down by the liver because it is conjugated to a long "tail" of sialic acid. This allows it to have a similar effect to the prolonged LH surge that normally occurs in mares. The chief advantage of hCG is that it is inexpensive. Also, contrary to an older belief that hCG induced auto-antibodies that resulted in diminished efficacy, hCG remains effective even if it is used repeatedly. Another benefit of using hCG is that current doses are much lower than those previously used (750 IU vs. 3000IU) further decreasing the cost of using this hormone. These advantages make hCG more popular than deslorelin in some practices. However it appears as though cost is not an important factor on many stud farms therefore deslorelin (Ovuplant) continues to be widely used in preference to hCG although there is no rational reason for doing so.

This lecture pertains to the female side of stud management only. Although this represents the lion’s share of stud work, stallion management, semen collection, processing and A.I. are of course of major importance!

To see a movie on the collection, handling and shipping of semen see your web listings.

This lecture pertains to the female side of stud management only. Although this represents the lion’s share of stud work, stallion management, semen collection, processing and A.I. are of course of major importance! To see a movie on the collection, handling and shipping of semen see your web listings.

Early pregnancy diagnosis is of critical importance on a stud farm. This is not only from the point of view of knowing that a mare is pregnant or not pregnant and should be rebred; it is critical for the management of twin pregnancies. Mares are first examined for pregnancy between 14 and 16 days after the presence of an intact follicle. This is because equine embryos are motile within the uterus up until about 16 days after ovulation. After that, it is very difficult to separate twin embryo units from one another so that one can be crushed safely. The problem is that we don’t usually know exactly when it is 16 days after ovulation because we don’t know when ovulation actually occurs. The reason for this is because we only visit stud farms every two or three days. Therefore when an ovulation is confirmed by ultrasonography, that ovulation could have occurred at any time within the 2 to 3 day period before that examination. It is impossible to say how old a corpus hemorrhagicum is by its appearance on an ultrasound image. If we underestimate the age of embryos and there are two of them present on day “14 to 16” it is quite possible that we could find ourselves dealing with a set of twins that is 17 to 19 days of age; too old for the safe management of a twin pregnancy. If we estimate the duration of pregnancy after the time when we lost saw an intact follicle, this problem cannot occur.

Great care is taken to examine all parts of the uterus during pregnancy diagnosis, especially the body of the uterus where embryos are often missed in one’s haste to withdraw the transducer. Sometimes these pregnancies are just on the inside of the cervix! After the initial diagnosis of pregnancy at 14 to 16 days, we will follow the pregnancy until there is clear evidence of an embryo separating itself from the walls of the embryonic vesicle at about 19 to 22 days of age. Additional examinations are commonly performed at about 28 days of gestation when the vesicle is approximately bisected by the yolk sac on one side and the allantois on the other. A heart beat can be seen clearly at this time and is usually in the range of about 200 to 220 beats per minute. Image F shows the anatomy of the chorion, yolk sac, allantois, amnion and the embryo itself at about 28 days of age. Later examinations for pregnancy are usually done at about 60 days for fetal sexing and at about four or five months to ensure that the pregnancy is progressing normally before the approach of winter.

Click here for interactive image

It is useful to remember the various profiles of hormones at play during pregnancy. This will help you to determine which tests to use to verify the status of pregnancy at particular times. It will also save you some embarrassment if you should choose to examine progesterone profiles during the last half of gestation.

As foaling approaches, so does angst in the owner. This is understandable because foaling is a very dramatic event. It is very difficult to predict the exact time the foaling but one tries to do this to circumvent foaling problems. These problems include such things as neonatal isoerythrolysis, ventral ruptures, maternal injuries and fescue toxicosis. One of the first signs of foaling is evidence of lactation (unfortunately, it is also one of the first signs of abortion during the last trimester). Before secretions are actually produced, the udder will remain flaccid for some time then we usually fill with colostrum very rapidly. This is worthy of mention because one must never forget that the antibody content of colostrum increases rapidly only at the very end of gestation. Therefore, if foaling is induced the quality of the colostrum will often suffer and failure of passive immunity (FTP) will be a problem.

There is no perfect device to determine when a mare will foal. An almost- ideal device would be one that could be placed across the cervix, to warn one of early cervical opening. Even this would not warn of transverse presentations. An excellent compromise is this FM transmitter (Foalert) that is fastened across the dorsal part of the vulvar lips. It is inserted when the mare shows the first signs of mammary enlargement. When the two sections of the device are separated by the advancing fetal membranes, the transmitter sends a signal to an alarm, cell phone or pager. In the experience of this author, this has saved the life of several foals.

When the mammary gland shows the first signs of enlargement, small amounts of milk can be taken for electrolyte measurement. Usually this is done as soon as the milk turns a smoky-grey to white color. As shown in the next slide, these results are interpreted using a table to predict if foaling is imminent.

This slide show the table just mentioned. It is used to make decisions about the safety of inducing foaling or predicting when foaling might occur. Using a combination of the calcium, sodium and potassium content of the colostrum, one obtains a score that indicates how close foaling might be. For example: If the calcium content is greater than or equal to 7 mmoles/L this is given a score of 10 If the sodium content is greater than or equal to 30 mmoles/L this is given a score of 15 If the potassium content is greater than or equal to 35 mmoles/L this is given a score of 15 Therefore the score for this sample would be: 10 + 15 + 15 = 40. This means that foaling is imminent and if required, foaling can be induced with minimal risk.

Your obligation during a foaling is to ensure that the amnion is transected as soon as possible. After that you will ensure that the presentation and posture of the foal are normal. The position of the foal will normally correct itself spontaneously. In general, one should intervene as little as possible. After the foal has been born, one should ensure that it has risen and suckled within three hours of its birth. Incidentally, the placenta should have been expelled within three hours as well.

When considering whether or not to induce foaling, remember that once it has begun, foaling cannot usually be stopped. Therefore the veterinarian must assume responsibility for everything that may occur as a result; good or bad. The moral of the story? Don’t foal with Mother Nature!

After all foalings, placentas must be retained by the stud owner so that they can be examined for completeness and normalcy by the veterinarian. Examination of the vaginas of mares immediately after foaling should be encouraged as a routine procedure on stud farms. Owners sometimes object to interventions done in the immediate post-foaling period but the early discovery of an anterior vaginal tear may prevent evisceration and save the life of a mare.

After every foaling, one must always ensure that the foal has obtained sufficient passive immunity. If there is any doubt as to the status of passive immunity, additional immunoglobulins should be given intravenously.

welcome to this lecture on the basics of stud farm...

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