Animal feed bag hereabout (7)

I believe the answer is:

herbage

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'animal' is the definition.
Although both the answer and definition are singular nouns, I don't understand how one could define the other.

I don't understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for herbage that I've seen before include "Plant life" , "Vegetation" .)

I've seen this clue in The Globe and Mail.

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