My friend did a test like this when I was pregnant and it was right!!! Haven't done it with the horse though!!! Not sure what point you would have to do it over! With me it was the back of my hand!
it is done with a nail & hair from the horses tail, and you hold it above the flanks, tis a bit of fun, my two the maiden is having a colt & the T.B. a filly, so we shall see
Oh crikey, forget the tail hair it doesn't make any difference unless it is all you have available. I use a bit of baler cord on an eye bolt held a couple of inches over the loins.
It has been 100% correct on whether my mares are pregnant, about 50% on gender. (I still get the Vet in to scan though)
My Vet thinks I am a total fruitcake, but as I'm British he accepts this as normal, but he admits that it does appear to work (his wife even tried it on my gelding and the stallion to check) my Farrier thinks it is hilarious and shows all his clients his 'party trick'
It does get a little confused and frantic when used on cats though.