Potatoes are full of carbohydrates and really help an animal finish but you will have to feed much more than 2 lbs. They are about 80% water so feeding 20-30 lbs/day would be more like it. There are two main drawbacks imo, Make sure sure you chop them up so they do not choke on them. The cattle absolutely love them and will really go at them hard and gorge themselves. Because of all the water, the manure will become quite loose. This is not really a problem in the feedlot but if these are show calves, more cleaning and bedding will be needed. Another way to feed them is to ensile them in a silage pit. There are usually some seed potatoes left over after the crop is planted and we put them in the pile as we are making it. The potatoes "cook" and basically come out as mashed potatoes with the skin on.