Also depends on the size of the bales and the weight of the tractor/fluid in tires etc.
For many livestock operations, the WEIGHT of the tractor is much more important than the hp. If you are talking about 5x6' large round bales, I would say that most 50 hp range tractors are not designed for nor safe for lifting 1500 lb bales that high unless fluid in tires and firm level ground.
If you are talking about smaller bales then maybe. Safety is number 1 concern. People are killed in tractor accidents way too often.
Jim