I had an experience with a set of live twins. Nothing to do with ph. One bull calf and one heifer calf. Assumed the heifer was free martin and sold it. kept back bull. Sent in th test for bull. I did not indicate he was a twin. He seemed to be clean by pedigree. Bull seemed to be clean but a little fuzzy. Anyway, got a th defective calf from bull. Apparently as I understand it....if you have a set of twins it is good to test both individuals even if you are are only keeping one calf for breeding. Somehow the twin affect blleeds over between calves and muddies the water somehow. If both calves are tested things can be cleared up.