I just tried this for the first time... Had a bull get hurt, and I needed to know if everything was pregnant or if I needed to be scrambling to find a bull for any stragglers. My vet was already there to take a look at this bull, so I had him palpate the cows I thought should be 40+ days. I knew there were 2 cows that had bred to the bull 29 days before, and I knew he wouldn't be able to pick those pregnancies up by palpating the cows. I had him draw blood on those two plus one more he called open, and I sent it to Southeast Animal Labs near Rome, Georgia (I'm in the Southeast).
Finding information about where to send the samples and how to package them was the biggest obstacle. I finally found the lab I wanted to use, printed off the instructions for packaging, and took the blood to the PO. Shipping & packaging cost $5.50 plus the $2.50 per sample for the tests, so it's cheaper than most anybody you can get to palpate cows. I figure it's safer on the embryo since it's possible to abort one palpating...I've had that happen a couple of times over the years, even with very reliable and experienced people doing the palpating. I've never been very handy at drawing blood, so that's something I'd have to get better at if I were gonna do a bunch of em. It's not as easy as it sounds, but it took my vet a few seconds. Pluses are it's very cost effective and it's safe, and I assume the results are at least as reliable as other methods of preg checking. The biggest drawback is waiting for the results which will be a few days by the time you mail samples, etc. I shipped my samples regular mail last Friday morning, confirmed yesterday that the samples had arrived at the lab on Monday, and she told me I should would have results by the afternoon (yesterday). I was disappointed when I didn't hear from anybody by the time I figured they would be gone for the day, but I had an email from the lab last night before bed time. Cows should be at least 28 days bred, and the test can't tell you how far along they are, just if she's pregnant or not. So I think it depends on your situation whether it's a better option than palpation to determine pregnancy.