Is it possible that was the case?

From what you post, it seems like you give them a more naturalistic environment, so that could contribute to less stress on them.

Sticking a wild hog in an inch of aspen would probably stress them out a bit.
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"What is man without the beasts?
If all the beasts were gone,
men would die from great loneliness of spirit.
For what happens to the beasts,
soon happens to men.
All things are connected."

-Chief Seattle (Duwamish Tribe)

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