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  Discussion on Using a recipient mare in winter anestrus to avoid having to sync mares??
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New Member:
pacifecm

Posted on Saturday, Feb 12, 2011 - 3:52 am:

We are doing embryo transfer with donor and recipient mares on opposites sides of the country (with utilizing vitrification or using a recip herd as back up if needed). The donor mare's vet says we can avoid syncing the mares if the recip is still in winter anestrus and the recip mare is given drugs (progestrone he may have said) to prepare her to accept the embryo, however she won't cycle her own first. I kept asking questions as to how that works and kept getting "it's like using a recip mare with no ovaries." Great answer, expect, I had no idea you could even do that.

Is this a viable option? When do mare's in the Northern US usually leave anestrus? We certainly don't want a foal born Feb 1st when it's 15 degrees at night. I know you can, but I don't want to. Is it possible to extend anestrus (I don't think I can take away sunlight).

And just so it's covered, yes, the donor mare is under lights and cycling regularly at this time.
Moderator:
DrO

Posted on Saturday, Feb 12, 2011 - 9:35 am:

Hello Kate,
Actually the work for ET into ovariectomized mares is quite old:

J Reprod Fertil. 1987 Jul;80(2):395-401.
Establishment and maintenance of pregnancy after embryo transfer in ovariectomized mares treated with progesterone.

Hinrichs K, Sertich PL, Palmer E, Kenney RM.
Section of Reproductive Studies, New Bolton Center, School of Veterinary Medicine, University of Pennsylvania, Kennett Square 19348.

Abstract
Pregnancy was established and maintained after embryo transfer in 3 ovariectomized mares treated with progesterone only. Four ovariectomized mares were used as recipients, and 7 transfers were performed. Progesterone in oil, 300 mg i.m. daily, was given starting 5 days before transfer of a 7-day embryo. If the mare was pregnant at 20 days, progesterone treatment was continued to 100 days of gestation. The 3 pregnant mares carried to term and delivered live foals with normal parturition, lactation and maternal behaviour. No differences were seen between pregnant and non-pregnant ovariectomized mares in jugular plasma concentrations of oestrogen, LH or FSH from day of transfer (Day 7) to Day 20. Pregnant ovariectomized mares showed a rise in LH, reflecting production of horse CG, starting at Day 36. Oestrogen values remained low until Day 50.

I must say I have not heard of pulling this little trick in mares during winter anestrus but do not see a reason it would not work. Extending winter anestrus: place the mare in a darkened stall starting at 4pm and leave her there until next morn should prevent the onset of spring cycling. Usually mares in the middle latitudes of the US begin with weak cycling in late Feb to Mar but the first successful ovulation in late March to early April. Far Northern latitudes would be a little later but I have no actual dates. It is very variable from mare to mare.
DrO
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