Has anyone experimented with using cow after birth on k-9s?

Yes. They are hard to work with because of their texture. Seems you have two ways to work with them. Either completely rotten down or semi dried to the point you can grind them. I use them some but haven't found them to be anything super great like I hoped. Ive heard discussions about aging them without air but haven't tried it.

I don't have experience with horse or cow afterbirth.

I do know that it was always a race between me and our LGD as to who got the lambing afterbirth. So fresh is also a possibility in a flat or dirt hole set, but it is not easy to work with other than a one piece and done type of bait.

Kansas trapline products has a lure thats after birth based called blood runner. Probly like everthing else timing when used and where is the key.

You'll hear a lot of people say that the coyotes are coming in to eat the after birth. Most adult cows eat the after birth of their young. So, the question is, why is there a lot of coyote activity around calving areas? They might get some that is left lying around, but not much. Are they looking for or eating something else? What's your thoughts?

I think they get more afterbirth than you may think. I know on the fall calving cows the vultures will come in flocks and that's mostly all they are eating. We also get quite a few eagles this time a year on our spring calvers. Coyotes also eat the crap the first day or two the calves are alive.