I can't imagine the herbicide is coming from the manure. More likely the compost. People put weed treated lawn clippings in the compost to be picked up for compost.
My neighbor treated his lawn with a broad leafed weed killer and when he mowed the lawn, he fed the clippings to his cows. They died. All three of them.

Actually, it was coming from the manure. If you read the article (link posted above) you'll see the chain. The manure used in the compost was being taken from several different dairies. The suspect herbicide is aminopyralid. The cows from some of the dairies ate the silage that had grown where that herbicide was used to control weeds. It apparently doesn't hurt mammals, but it passes through them unchanged. So their manure carries enough of the potency to kill broad-leafed plants.

It was said "mowed the lawn, he fed the clippings to his cows. They died. All three of them."

Are you absolutely certain? If so, what was the active ingredient?

"It was said" ??? What are you referring to?

I'm referring to the first response to OP's thread given by botann z8 SEof Seattle

My neighbor told me he put WeednFeed on his lawn. I suppose it was 2-4-D that killed the cows.
I should have read the article.

Yes, I'd be concerned about aminopyralid in the manure. What about the milk? Is it in that too? It wasn't mentioned. I wonder why.

"The Bottom Line
 The best sources for pesticide-free compost are those that have been analyzed and certified.
Home-made compost is also a good choice as long as you are sure your materials are
contaminant-free.
 Unregulated compost can contain pesticides, heavy metals, and other environmental toxins that
may be harmful to you and your plants.
 If you must have your lawn sprayed with persistent, broadleaf herbicides, be sure to use a
mulching mower and leave the clippings in place. Do NOT compost them or bag them for clean
green removal.
 Soil testing for heavy metals is crucial for any landscape where plants are grown for human
consumption"

Here is a link that might be useful: The Myth of Clean Compost

My thoughts exactly.
Mike

One more reason to use real compost, instead of the manure-sawdust or manure-bark mixes that are becoming so common nowdays.

I would imagine that many people do put lawn clippings in their yard debris bins when they do use Weed n'Feed products instead of leaving them on the lawn.