Egress-fence failure when only part of animal is out?

Need legal definition of egress in terms of lawsuit. Does this apply to the whole body or can egress apply to part of the body? Ex: a fence is meant to prevent eqress of
an animal. The animal's head and neck go 1) over the fence and cause
damage or 2) through the fence and cause damage. Has the fence failed to
prevent egress? Thank you.