Surprise surprise! Dogs don't like being treated unfairly. A researcher has found that if dogs are not given the reward that they see given to other dogs they stop cooperating. I'm surprised it was thought worth doing the experiment. Unless dogs had minds totally different from ours they were bound to dislike unfairness. The same would surely be true of any social mammal. The technical term invented for this by the way is 'inequity aversion'.
What is astonishing is that so many people think that human society can be run with a level of unfairness beyond anything any other species has experienced. If the gap between the rich and powerful and the poor and powerless is too big, then of course the poor stop cooperating, beyond the bare minimum that they have to do to stay alive. In my lifetime we have gone from the extreme unfairness of the 1930s, through the increasing fairness of the post-war years and on to the record breaking unfairness of the past 30 years. If we do not greatly reduce the inequalities within and between countries, our world will fall apart in a chaos of war and plunder.