An device used to measure antifreeze in your car radiator will suffice. If all the balls float, you can assume the colostrum to be of good quality. This corresponds to a specific gravity of about 1.060. Of course, this is a rough estimate. Once the foal nurses, you can measure the IgG content at 18-24 hours after the foal nurses.
Several tests are available, some even foal side.
The Cite Test can be performed on whole blood, plasma, or serum and can be done on the farm. Treatment of this disorder depends upon when you detect a problem. If the foal is over 24 hours old, a plasma transfusion is required to bolster the IgG concentration. The foal may need between 1 - 3 liters. Plasma administration should take place over several hours, however, it may not be practical to administer it this slowly.