Maybe jumped the gun here.
After doing a bit of research (its a bit difficult to understand all the cattle breeder talk) but I did more searches on the other cattle implants. Namely Synovex H...guess what. Looks like you are not supposed to breed cattle that has been treated with that implant either. Synovex H is just Test Prop & Estradiol!! Never heard of any birth problems from guys hittin test prop.
If this is correct then my conclusion is, that the reason you cannot breed these animals (after being implanted) is not birth defects or things of that nature but simply because the FDA does not allow you to breed implanted cattle plain and simple.
Again I could be wrong here. But that is the conclusion that I have come to.
-GP