[Tucker39]

Down on the dairy farm, my Dad made every effort to prevent any cow from eating her “afterbirth”. He claimed it decreased their milk production if they are it. I can’t see any benefit to cattle in eating it. AFAIK, they are pretty strict vegetarians all their lives. Certainly not carnivorous.

[Battle Axe]

In the wild, the mother will eat the placenta so that predators will not know she has given birth. Newborns are a prime target of the predators.

Some dairy cows will eat it and some won’t. I did have one cow that could not digest it after she ate it and became quite septic.

[gundog]

Probably mostly to keep it from attracting predators. I wouldn’t think that a jolt of animal protein would hurt milk production, much. But, what do I know? Dairy cows were bred to crank out milk in a protected, artificial environment. Raising a calf has different requirements. Seed and nectar eating birds feed their offspring insects, as they need protein that the sdult’s diet would not provide.

[Tennessee Conservative]

I think it’s instinctive from their wild days to keep predators from smelling the afterbirth and attacking them since the newborn isn’t able to run yet. Wild animals do it for that reason and I think it’s a leftover instinct in domestic animals.

[Mrs. Don-o]

Isn't that where Bovine Spongiform Encephalitis ("Mad Cow Disease") came from?

IIRC, it was due to an infection by a misfolded protein, known as a prion. It resulted from the practice (widespread at the time in the UK) of feeding meat-and-bone meal to young calves of dairy cows.

From there, the prions spread to humans, resulting in a kind of Creutzfeldt–Jakob disease. No cure, sometimes fatal. And it doesn't manifest until maybe 4-5 years after initial exposure.

Prions. From same-species flesh. Not part of a good, balanced diet.

[Albion Wilde]

Down on the dairy farm, my Dad made every effort to prevent any cow from eating her “afterbirth”. He claimed it decreased their milk production if they are it. I can’t see any benefit to cattle in eating it.

It's an instinct in many kinds of mammal moms, thought to be a protection for the helpless newborns so that predators won't smell the blood. Most mammal newborns have a pleasant odor (once bathed) that helps fool predators (and also helps create bonding with its relatives); but the placenta apparently smells tasty to wolves, mountain lions, etc.

So it's rather affected as well as disgusting for human moms in comparatively secure circumstances to do this.