This was posted years ago by pintopiaffe...great info so just pasting for everyone...The only thing I would add is get pH strips that go to 6.2 (or even lower). When milk tests that low it is a sure sign of "coming soon"
Milk Testing 101:
Step #1: Get milk. Not so easy. You must convince mare, once she has sufficient udder, to 'let down.' Think foreplay. Massage, a little baby oil can help, warm wet washcloth... then some poking, like a little baybe nose would do. Next, strip out a bit of milk. First squirt or two goes nowhere, it's not accurate. You need only about 2 good squirts, or way too many itty bitty squirts. Collection container can be a nifty little plastic cup like
a Nyquil cup, or, (my favorite) a shot glass. Shot glass cleans easier, and somehow, seems more appropriate.
Step #2: Observe. First milk will be like water. You don't even have to waste a strip on this. next will look like Pee. Clear but yellow in color. This is often preceded by a very thick, sticky, clear stuff. Dunno what that is. Won't test, don't bother wasting a strip unless you are *reeeeealy* anxious. I know you're tempted since this is the first sign of 'change' and is sticky... o.k., go ahead, try it. I'm right.
Next will change to lemonade. That's when you start testing. Next will be lemonadey, but with tiny, tiny flecks of white. closer still... Final change will be to cloudy/grey/bluish. If you're brave, taste a drop or two. Early milk will be salty. When she gets close, it will be sweet, or to me, 'rich' like the taste of cream (which I don't think has so much a taste as a 'texture' or aftertaste.)
Stickyness is worth noting too. Early, early stuff--the clear, thick goo is sticky, but later, when the milk dries on your fingers, if it's sticky and flakes like sugar water drying--you're closer.
Step #3: Testing Equipment and procedures. You may buy the "Mare Foal Predictor Kit" (Jeffers is cheapest I've found, 1-800-Jeffers) which makes you feel like Beakman (luved that show!) and is pretty user friendly, or the Chemetircs "Titrets" (just the name makes me laugh! punch... ) which are also supposedly user friendly. (Haven't ever braved them, so this post only applies to 'strip' tests.) OR, you can build your own kit for about $20 LESS than either of the above by buying Water Hardness test strips. Best brand I've found is "AquaChek" which tests calcium only. A local pool shop was able to order these and have them in 2 days for me.
EVEN BETTER are Hot Tub strips. Four-or-five-way strips which test calcium, pH and some other stuff that mares really don't care about. I use "Baqua Spa" and "Soft Soak". Both are made for Bromine-Free, Chlorine Free Spas & Hot Tubs. Readily available, cheaper than the Aqua check (which is weird, since they have 4 in 1 tests) AND have the added entertainment value of pH testing. Brand isn't important, what you're looking for is a test that measure Calcium as CaCO3 in Parts Per Million (ppm) from 100-500 at least. As I said, a pH test is bonus fun.
-You also need some type of small (5cc) test tube or larger than 3cc syringe with cap, a 3cc Syringe, a 1cc syringe (insulin syringes are perfect) and, the magic potion: DISTILLED WATER. This is the secret "testing solution" in the commercial kits. The key is it has no inherent minerals, so the test is accurate.
-Ratio for testing is 6 to 1, or 3 to 1/2. For me, all I can ever get early on is 1/2 cc of milk, so I use 3cc of distilled h20 to 1/2 cc of milk. Mix 'em together, WELL in mini-test tube or syringe.
-Dip strip for one second. Do NOT shake off if it's the spa test strips. DO if it's the others. (i.e. follow the directions for the particular strip)
Step #4 Time, observe and bang head against wall... The calcium only strips show changes in 15 seconds. pH at 30. The mare strips are supposed to be checked at 1 minute, but if you see earlier changes, that's good, and part of how you figure how close you are.
Step #5 Interpreting results:
Calcium: Less than 100 ppm, you can go 2 days before rechecking unless you notice other, significant changes. Above 100ppm, but less than 200 ppm, check daily, in the evening. Once you hit 200 ppm, you've GOT MILK. 90% of mares will foal within 24-48 hours. Over 500 ppm, camp out in the stall, here we goooooo....
On the mare strips, 1-3 squares in a minute, 2 days before next check. A FAST three though, recheck daily. 4, something like 80% chance in 24, 5, within 12 hours. a FAST 4 or 5 and buckle in, we're off...
pH: Found out by accident when I couldn't get my regular calcium strips how useful this is. You CAN test pH, and it's actually a very reliable and easy indicator! pH will be well over 7 up until you've got Colostrum (over 8.4, the "high" test on the spa strips) When you get colostrum, pH will drop to below 7. The information I found is when it gets below 7, you're within a few hours. This second measure is INVALUABLE test could be helpful for a mare who has a high calcium count for a couple of days. The pH will not drop until just before foaling. She WILL GO within 6-24 hours.
**adding** the pH is a DRAMATIC change. All the strips I've used have been 'fuschia'' color at the high end, and yellow at the low. When the milk has changed, it stays VERY yellow. BUTTER yellow. Below 6.8, off the charts low. I know it's exciting when it is peachy, and that means things *are* changing... but you still could have a day or two to go--for me it means testing at least every 8-10 hrs. once I see it start to drop.
Finally, it's really, really obvious in the test tube with the water what you've got. After doing this a few dozen times, I've noticed the milk that is real MILK, i.e., close, stays in suspension. With just half-a cc in the tube, the entire sample looks cloudy, like you put water in a not-rinsed-milk-glass. It STAYS this way. Earlier samples settle and need to be reshook. In the end, all the evidence leading up to dipping the strip tells me my answer, I just like the empirical evidence to justify booking out of work.
Obviously you have to take in these results with an eye towards other signs like dialation/elongation of the vulva (we really can't 'see' dilation, but some folks refur to the vulva changes as such,) softening of the tail head etc. And the standard disclaimer about maidens apply: they break all the rules, so don't RELY on any signs at all.