Hello...
My friend has a colostrum refractometer, which we were using to test the milk to see if there was a correlation between the level of colostrum and then when the mare foaled.
This tool is SUPPOSED to be for testing the milk to see what quality of colostrum the foal is receiving. Right after the mare foals, but before the foal nurses, you are supposed to test.
Well the mare last month that we tested, tested VERY GOOD (27) and foaled THREE DAYS later. Unfortunately, she was also dripping milk. We watched the level of colostrum then drop over the few days down to 13. The iGg test on the foal is very low.
I don't think that it is an accurate tool for predicting a foal, but it can be an additional element you can use to see how close they are.
Andrea