alert(myJSON) outputs:
[{"breed":{"msg":"Breed is required","placement":"#breed_error_1","return":"false"}},{"breed":{"msg":"Breed does not exist","placement":"#breed_error_2","return":"true"}}]

$.ajax({
            type: 'POST',
            cache: false,
            url: "validate_breed",
            data: element+"="+$(elementSelector).val()+"&v="+validateElement,
            context: document.body,
            dataType: 'JSON',
            success: function(myJSON){
                alert(myJSON);

                for(var i=0;i<myJSON.length; i++){
                     console.log(myJSON[i].breed.return);
                }
            }
        });