Twenty-eight-year-old Mickey was bitten on the face by a Staffordshire pit bull terrier-type dog while he was resting in a field in Immingham.
It is thought the dog was one of three which went into the field from Homestead Park.
The attack caused Mickey to employ a donkey's natural defence tactic – lowering his head and charging.
Ellie Hickson, 12, cares for Mickey and his pal Murphy when they are resting after a summer in Cleethorpes.
The Oasis Immingham Academy student said: "We heard the donkeys screaming at about 8pm and I saw a dog run off.
"It wasn't until the morning that we saw Mickey had blood on his face. They wait for me every day after school. Mickey is the boss and looks after Murphy."
The family were put in charge of the donkeys' care after their owner, Mike Wade, appealed in the Telegraph for winter grazing land.
Ellie's mum Hayley Cowen came forward and has also called for dog owners to ensure their pets are trained properly.
She said: "The donkeys were fine before with our two dogs, but now they are wary. A couple of days later, a dog killed two of our chickens, injured another and hurt one of our ducks. It makes me angry that irresponsible owners let their dogs loose into our private property."
The donkeys will return to Cleethorpes at Easter, and it is Mickey's last year before retirement.
A spokesperson for Humberside Police said: "Two men and a woman were walking three dogs in Homestead Park when the dogs got into a field where the donkeys were situated.
So basically they fled the scene with their vicious dog?
"It is alleged the dogs attacked the donkeys and one sustained facial injuries. Local neighbourhood officers have made attempts to locate the owner of the dogs and attempts will continue to do so."
A spokeswoman for the Grimsby branch of the Blue Cross Animal Hospital also had tips for dog owners.
She said: "Try to socialise and train your dog with donkeys/horses from an early age, so they are not a scary or exciting thing to come across.
"Ensure you have your dog under close control and have a reliable recall through training. If you do not have a sound recall, please keep your dog on a lead."
Giving nice tips to irresponsible owner in the hopes that they'll be responsible is a waste of time. It's like doing a public service announcement reminding people that they're required to have auto insurance. The scofflaws/criminals don't care and won't change.
(This is Grimsby - Mar 8, 2013)
