Monozygotic Twins; Identical Twins?

[FatCatFarm]

A dutch warmblood mare I had sold in foal and who was 5 days past her due date, was delivered of deceased twins from the same placenta yesterday morning. Both twins had to be pulled as the mare experienced a dystocia. At first I thought the vet must have missed twin embryos on US but was told he was astonished to find twins and only one placenta. Very rare as I understand it. Fortunately the mare is reportedly recovering nicely.

The owner said the vet characterized them as identical though she said their markings were not, despite there being only one placenta, I would imagine they were genetically identical. Both were chestnut fillies with lots of chrome.

Anyone else ever have this happen?

[stoicfish]

The owner said the vet characterized them as identical though she said their markings were not, despite there being only one placenta, I would imagine they were genetically identical.

The particulars of markings are not determined by genetics so that makes sense. Clones do not share the exact same markings either.
Twins are very rare and I imagine this is more rare. But that is hard to know as many people do not find out. (sex is the give away and color but after that, it would be hard to know)
Identical twins can have their own placenta also.

[FatCatFarm]

[QUOTE=stoicfish;8084230]

Identical twins can have their own placenta also.[/QUOTE]

I did not know that. Interesting to know.

[Hillside_H_Ranch]

True “identical” twins, i.e. twins that developed/split from a single embryo have been reported in horses, but literally only a handful of times. It is extremely, extremely rare. I would not diagnose the type of twins based upon how many placentas seemed to be present. But it is interesting!

[SouthernYankee]

Just out of curiosity how was the mare bred? Live cover or AI?

I ask because the likeliness of twins goes up when the mare is bred via AI. The last time I bred was with AI, and mine had twins on her 10 day check. Vet came back at 14 days and removed one of the embryos.

[stoicfish]

[QUOTE=SouthernYankee;8084835]
Just out of curiosity how was the mare bred? Live cover or AI?

I ask because the likeliness of twins goes up when the mare is bred via AI. The last time I bred was with AI, and mine had twins on her 10 day check. Vet came back at 14 days and removed one of the embryos.[/QUOTE]

Fraternal twins are very common. That is the result of two eggs being dropped and the interesting thing is that it may be as common in live cover but not as many live cover breeding’s are checked with ultrasound. With the exception of the Tb world and I believe I saw a article that said it was probably more common in horses at the end of a season but only recently observed with ultrasound.

[FatCatFarm]

The mare was bred via AI and was ultrasounded to rule out multiple embryos and only had the one. She was bred in late April for an end of March foal. Her last ultrasound was at 40+/- days. My vet did the AI; the mare was sold; and her current owner had her vet check her in foal via ultrasound twice. In fact, on her first US, around day 18, her vet declared the mare not in foal and came back a week later to flush her, and in abundance of caution, re-ultrasounded the mare and found the embryo; and then came out two weeks later for a recheck with a follow-up ultrasound and confirmed the embryo was “growing”.

A possible red flag that she was carrying twins was a comment her owner made to me that she thought the mare was already showing a lot when presented at a Keuring in September. I saw photos and did not think her particularly large though and this was her third pregnancy.

I wonder what the chance of this occurring is, 1 in 100,000 - more? Her owner is not a breeder and bought the mare more as a personal riding horse with her being in foal a happy bonus. Such a shame. As one would imagine, she’s a bit traumatized by the outcome.

[Hillside_H_Ranch]

No. The mare did not have only one embryo. Even if it was truly an “identical twin”, the splitting of the embryo occurs prior to even the 14 day check. The division occurs very, very early in the pregnancy; close to conception. So yes, the vet did miss the second pregnancy at every check, which is hard to conceive of at 40 days, when two large pregnancies with heartbeats would have been present. As far as I can tell from a brief search of the literature, there are only 2 or 3 reported, verified incidences of identical twins in horses. I’m sure there are more, but those are the reported cases.
And no…AI does NOT result in a higher number of twins. Twins generally occur from multiple ovulations in the mare, so has nothing to do with the type of insemination or breeding. In fact, TB mares have a higher incidence of twinning than most other breeds, and those mares are almost always bred in a live cover situation.

[Home_Again_Farm]

My only case of twins being carried long into a pregnancy was from a cycle where the vet never worried about twins because she was absolutely certain that the mare did not double ovulate. Obviously, that vet was wrong.

I have always checked and rechecked since that sad situation. Mares often produce multiple embryos. My latest repro vet also has told me that there seem to be many multiple ovulations when deslorelin is used during a cycle.

[FatCatFarm]

Wait, if I understand the process of identical twinning correctly, one embryo divided to produce two, yes? But could they be so close together as to appear as one in the case of identical twinning?

I can see where in the case of double ovulation, twins can be missed because that’s two separate embryos floating around separately. Or do identical twin embryos do the same thing once split?

The reason I ask is the owner’s vet is a vet whom I no longer use because he missed two sets of twins for me in the past. I had brought this fact up to the mare owner when she bought the mare and planned to use him to manage this pregnancy and then again when she told me what the outcome was just via text message and I didn’t have all the details thinking well, I did warn her about this guy. But then she told me they were identical with one placenta so I just assumed they would have appeared to him as one embryo. Thanks!

[FatCatFarm]

I just talked to the mare owner again and yeah, I do now think this vet dropped the ball and didn’t know what he was looking at when at 18+/- days there were twins and he misdiagnosed it as a fluid collection because he thought what he was looking at was too large to be a pregnancy. Geez!

[Home_Again_Farm]

My bet is that he can’t count placentas, too. :winkgrin:

[FatCatFarm]

I’m with you there! Poor mare!

[Hillside_H_Ranch]

[QUOTE=Home Again Farm;8085721]
My bet is that he can’t count placentas, too. :winkgrin:[/QUOTE]
This would be my bet, too.

But to answer the question, no…identical twins would not behave or appear any differently on ultrasound. They are two separate embryos, and would appear the same as any other sort of twins. This is, unfortunately, just a case of undiagnosed twins.

[FatCatFarm]

Thank your for sorting out my erroneous assumption based on the information I had to hand.

[Nadia]

I bred my maiden mare last year . She was checked at 16 days and vet saw 2, so he took out the small one. He wanted to do a recheck in a week and she had twins in one sack. We were planning a trip to Davis to reduce one, but on the recheck before Davis, she seemed to be losing one of the twins…We waited another week and the recheck showed that she now had one healthy embryo…Perfect …fast forward six months, and she aborted the pregnancy…she had twins…2 sacks…so she actually conceived quads! We were all stunned !

[FatCatFarm]

Wow Nadia, so sorry!

[Nadia]

Oh, thanks…I really should stop reading this breeding forum…It makes me sad.I lost the mare to an inoperable lipoma on New Years Day…Owning horses is not for sissys

[elizabeth_Callahan]

There have been multiple cases now of twins that have occurred after the transfer of a single embryo at 7 days into the recip mare. Itis rare,but can happen.