05-01-2012, 11:05 PM
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Somewhere between 60 and 90 days the weight of the foal in the uterus pulls the uterus over the pelvic rim into the abdomen. When you palpate a mare from that time until 7 or 8 months (and sometimes longer), the uterus cannot be found. You have to determine pregnancy by feeling the ovaries as they are being pulled down and have taught ligaments that can be felt pulling on them. You also go by the lack of being able to cup your hand over and around the uterus. An empty uterus will be flaccid and easy to get around. You can follow it from one ovary to the other.
Sometime after 7 months (varies from mare to mare) the foal is big enough that you can literally run into it in front of and under the ovaries somewhere. At about 9-10 months, the foals head should be in the birth canal and a person can feel it - hopefully, if it is in the correct position.
I still prefer rectal palpation over ultra-sounding after 25 days. I can sometimes pick up a foal at 22 or 23 days and occasionally it take up to 28 days if the pregnancy is in the body of the uterus instead of one of the horses. US is very useful if you have a double ovulation and you are checking for twins, but I see more mistakes made with one of them than an older Vet that has palpated hundreds of mares. I've been palpating them for about 40 years, so I am very comfortable with it. I have found that many young Vets neverlearn to get very good at it and just depend on US them.