When an escaped and injured circus wolf is found in the bush, a selfish boy denied owning a dog nurses the wolf in his wardrobe hiding it from his mother’s prying eyes, a determined dog catcher and the cruel circus owner who wants to give the wolf to an animal testing laboratory.

You have too many antagonist in the original logline, that doesn’t mean they shouldn’t be in the script, it’s just making the logline a little long.

Here is a logline attempt with only one antagonist:
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“When he saves an injured wolf from a cruel circus owner, a selfish boy must hide the creature or lose the lupine to the lab to which his former owner has sold the beast.”
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Hope that helped, good luck with this!