STUD NOTES

MANAGEMENT OF TWIN CONCEPTIONS

WHAT ARE THE OPTIONS?
At Yallambee we are not at all concerned about breeding a mare that is likely to have a multiple ovulation. We rely on our management to overcome the events that may unfold as a result. There are two extremely important dates we keep in mind when dealing with twins. Sixteen days post ovulation and 36 days post ovulation. Their importance will become evident further in the text.

The very first thing we do is map out any cysts in the mares uterus. Cysts experience very little, if any change during the breeding season. Also they do not move around in the uterus. Thus, if we confirm cysts - their shapes and position - prior to breeding, we are in good stead for accurate pregnancy diagnosis on our very first test. The greatest relevance of cysts to multiple conception diagnosis is that some can look awfully like a pregnancy, or if there are so many of them, it makes accurate pregnancy diagnosis very difficult.

We will always breed any mare that is ready for breeding, regardless of the fact she is likely to have a multiple ovulation. We are delighted to have multiple ovulations, especially in the mare of questionable reproductive capability. To us it means we have a greater chance of achieving our first objective - to get the mare in foal.

DIAGNOSING TWINS
Best practice is to have a fairly accurate idea of when ovulation occurred - it is more relevant than the service date in this regard. The ovaries are scanned for ovulation/s, after service (probably about 48 hours). The number and side of ovulation/s are noted. Should there be any other mature looking follicles still remaining are re scanned for a possible asynchronous ovulation 2 or 3 days later, and this information is also noted.

If only a single pregnancy is found from known multiple ovulations, especially the asynchronous example, a subsequent pregnancy test should be performed a one or to days later, depending on the initial ovulation circumstances.

The timing of the initial pregnancy test is important. Ideally at 13 and not more than 14 days post probable ovulation date should be when the initial pregnancy test is performed. We like to diagnose and have dealt with twins before they undergo embryo fixation at 16 days.

Assuming diagnosis of twins has occurred before fixation, crushing one of the embryos is a relatively simple procedure. At day 13 the embryos are mobile, and of a size that are quite easy to diagnose and manipulate. This is an extremely advantageous to the vet when twins occur as we have all options available to us in our subsequent management. If they are not big enough to do the job simply, then we revisit the procedure the following day.

Upon initial confirmation of twins there may be one of four scenarios:

1. The twins may be well apart,
2. They may be close together, but not touching,
3. They may be adjacent, and touching, or worse shadowing (one behind the other)
4. Age disparity resulting from asynchronous ovulation

Scenario one is a simple routine matter of crushing one twin, allowing selection of which is to go.

Scenario two is also relatively simple, but one of the embryos needs to be moved away before crushing takes place.

Scenario three is more difficult. Diagnosis can be more difficult, as twins may be so close, that only an impression of their presence may be detected. In these cases there may be multiple looks and/or attempt to eliminate a twin.

These twins need to be separated before crushing can progress. As the twins are mobile, the simplest and most sensible procedure is to put the mare to one side for a period of time. Usually we will continue to complete the rest of the veterinary session. We will then re-present the mare to the vet. Quite often on a second or subsequent look, we find that the twins have moved far enough apart on their own accord. If this is not the case, there is always tomorrow for another look and opportunity to perform twin elimination. This of course is dependant on a 13 or 14 day diagnosis.

Scenario four, provided still mobile the older of the two conceptions is likely to be the chosen one to eliminate for the simple fact it easier to maneuver and physically crush.

As intimated above, usually there is a degree of manual separation of the twins is often required of the vet. If crushing occurs with twins in a close proximity, then we are at great risk of damaging the remaining embryo. The fluid released from the crushed embryo may affect the viability of the remaining embryo.

By carefully maneuvering one of the twins away from the other, up to the tip of a uterine horn, the embryo is subjected to the pressure of the ultrasound transducer and the pelvis, and then crushed. Generally the vet will do this procedure in a sweeping action, always monitoring the whereabouts of the desired, remaining embryo, and then back to one they are trying to move. Some veterinarians prefer to perform this procedure with the assistance of a rectal relaxant. An uncooperative mare in the crush can make this a difficult task. Tranquilizers may be used to calm the fractious mare.

Once crushing has successfully been achieved we routinely give the mare a drug that has an anti-prostaglandin effect. Whether this is of any help or not is open to debate, but it does make us feel better that we have done all possible to protect the remaining embryo. The mare will be re-examined 3 days later to check that growth has occurred (remembering that growth is rapid at this stage and the embryo will have nearly doubled in size in this short space of time).

If growth has occurred, then there is no reason that the single embryo has any less chance of survival than a normal pregnancy. An unsuccessful crushing will nearly always be confirmed on this follow up examination, in which case we will immediately bring the mare back into season with the use of prostaglandin drugs.

Twins verified at 13 days post ovulation. These were manipulated: The larger of the two was (squashed).	The same mare two days later, with only a single growing embryo. Note that the scale on the scan is the same as the picture on the left, indicating how much an embryo grows at this stage.

Should twins be discovered after fixation, and they settle together (as a great many do), then our options are much more limited. The following management will also apply to those twins that are inadvertently present at the 27 days, or later pregnancy testing.

Unless twins are well apart after fixation, then crushing is may not be the recommended option. Veterinary research suggests that approximately 70% of twins will naturally result in one embryo remaining by day 40 under these circumstances. So the way to go here is probably sit it out, monitoring the pregnancy. This is the point where day 36 comes into play.

Endometrial cups form between day 36 and day 40. If a pregnancy is aborted after this time there is very little chance of the mare coming back into season to be re-bred that year as the cups produce progesterone and prevents the estrus cycle.

If the time of the breeding season allows for re-breeding, and this is the desired course of action, then abortive measures must take place before day 36 (about 30-32 days). If the time of season does not allow for re-breeding, continuing to monitor the pregnancies for one to go naturally is an option. This may extend out to as far as day 60 or 70 before abortion is again reconsidered.

There is one further successful procedure that can be used to reduce a twin pregnancy to a single pregnancy. However, it is a surgical procedure that requires an expert to perform. A needle of potassium chloride or penicillin is injected directly into the heart of one of the fetuses'. The preferred time frame in which to perform this procedure is between 70 and 110 days.

All mares are carefully re-examined for the possibility of twins at their routine 27 days pregnancy test. This is especially the case with those mares that had a known multiple ovulations and a single embryo diagnosed on the initial test.

We have had twins in extremely cystic mares that have got out to 25-27 days. The reason for this is that diagnosis is virtually impossible until we have discernable heartbeats and embryonic girdles. These mares are the heartbreaking group, as they are probably reproductive problems anyway. Generally this group we will sit on, hoping one will go naturally if crushing is not an option.

Despite all efforts, twin conceptions can eventuate from a mare that appeared to have only a single ovulation. Therefore, whenever we pregnancy test a mare (whether she has had a known multiple ovulation or not) we assume there is a possibility of multiple conceptions occurring.

With the extremely high success rates (about 95%) of the experienced veterinarian manipulating twins in early pregnancy, I see no need to sit and wait on a multiple pregnancy that may or may not sort itself out. We will nearly always opt to crush a twin. If record keeping is accurate, scanning is professional, and mares are presented at the right time, then twins are not an issue of concern.