We test every foal here within 12-15 hours after birth and the foal has nursed for IGG levels. My vet says the new recommended level should be greater than 800. I had a filly born three years ago where she was up almost immediately, frisky and nursing well. I had the IGG test done within 12 hours of the filly nursing, but as soon as the vet got the results (within half hour when she arrived back at the clinic), she called me and said she was coming back out because the IGG level was only 578. The vet gave the filly synthetic plasma to bring the levels up and, again, we had to wait 12 hours... but that still did not do the trick. The next day the vet came to give the filly plasma via IV (costly, but I would have gone this route in the first place had I known the synthetic stuff does not always work). Finally, after another 12 hours, her IGG was 2,000....but, in the meantime she developed joint ill in her left hock and had to have it flushed every day for two weeks, she was on antibiotics for a month and a half and had to be confined to a stall the whole time to keep her from running and weakening the hock joint. Long story short and after almost $4,000, that filly survived and never had any problems after that. I doubt she would have made it had I not tested her initially, and the plasma via IV did the trick but not before her immune system suffered. The dam was bought a month and a half prior to the filly being born, and the dam was severely underweight when I got her....I attribute that as the reason for the low IGG levels because the dam was not producing good colostrum, even though the milk looked normal and the filly was nursing furiously! The next year, this dam was fat and sassy and had a perfectly normal, healthy filly. I do hate to pay a farm call and pay for the test (costs keep going up), but it is really worth it in the long run. I always get the vet to give a Tetanus Toxoid shot to the foal at the initial vet visit as well.