Any kind of cardio competes with overal calories, fat/carbs/protein, essential aminos, vitamins and minerals that your muscles need for recovery. If you are serious about gaining mass, you;ll need to add an extra 600 calorie meal for every cardio session you do. Also, don't go running or do cardio that's hard on the legs for at least 3 days after a leg workout---you'll just hinder the recovery. Lastly, don't do cardio within a few hours of weight training. Doing cardio before drains you of energy you need to lift hard and heavy. Doing cardio after depletes glycogen stores so far that recovery is drastically impaired. I do 30-45 min on the tread mill every 2 weeks while bulking just to keep fit. Anything more is just detrimental to bulking.