Just to clarify, Cavy Cuisine is for pigs over 6 months, Cavy Performance is for pigs under 6 months. The reason it is like this, is because Cuisine is timothy based and Performance is alfalfa based. Young pigs need alfalfa because they need the higher levels of calcium found in alfalfa to grow and develop properly. If you can only get Cuisine, that is fine. You can give your pigs alfalfa hay as well as a grass hay, or supplement with veggies that are high in calcium such as parsley. Have a look at Ly&Pigs food chart for other veggies high in calcium.
That being said, don't overdo the calcium! Pigs can develop sludge in their urine which can lead to stones. It should also be said that there have been cases where Oxbow causes powdery urine for some reason. Bpatters has a running list of these cases, so you could always ask her if you would like more info.
I also wanted to add, that Kleenmama and Sweet Meadow are other options for pellets and hay. Kleenmama is said to be the best, but you can only order it if you live in the US.