Studies right now are showing that drinking milk after working out can promote muscle growth and actually reduce weight gain. But the studies are based around drinking about 2 cups of milk after exercising.

Other studies have shown that drinking to much milk can have long term effects from the increased calcium like creating bone spurs. Not to mention you are increasing the amount of build up of the hormones farmers are using on cow's to increase milk yield in your body. There are no proven studies yet - but the fact remains.

So what it means if you are trying to build muscle mass then drink some milk after an intense work out. A gallon of milk isn't doing you any real benefit.