These are things I try not to think about. And not just with animals: plants have grown from and frequently come in direct contact with poo, and that's not a great thought either. Maybe it will be easier when vat grown meat scales up.
We have the water cycle, the carbon cycle, etc. The planet is reusing materials all the time. Thus, some of your clean drinking water was someone's pee at some point before.
I don't see why that is gross at all. Drinking actual pee would be super gross. But drinking water that used to be pee is still just water now and that's all the matters.
I've pointed out that soil is already loaded with remains of dead animals. But to no avail.
By definition decomposers are converting the animal products into basical minerals and nutrients because THEY are eating the meat.
Otherwise plant matter couldn't even be eaten because some of the carbon has been through the carbon cycle and was previously an animal.