The delicious natural treats for small animals are made of 100% all-natural alfalfa and contain no artificial glue, sticking agents or cardboard.
The Alfalfa Chew-nels’ unique tubular or tunnel-like shape will entice small pets to play and hide in them, as well as promote natural chewing and nibbling. The chew tubes are extremely durable and will hold up to your small pet’s constant chewing."
These are basically cardboard tubes covered with alfalfa hay flakes. I have one in medium, which would work for smaller pigs, and one in large. The pigs like them so far (which is not surprising since they love cardboard and they love food). The boys nibbled on the ends of their tube while the girls ate the hay off the sides of theirs. They enjoy running in and out of them like they do with regular cardboard tubes. The alfalfa hay does flake off a bit, so if you use fleece bedding it can get a little messy. That would be my main complaint about these. Also, I wish they were made with timothy hay instead of alfalfa, since you shouldn't feed guinea pigs alfalfa hay after 6 months, but I figured the amount of hay on these tubes wouldn't make much of a difference. I can see these tubes being very useful boredom busters if you have to leave the pigs alone for a little while. The best thing about them is how durable the cardboard tubes are! I have had them in the cage for weeks now and even though much of the alfalfa hay is gone and the pigs nibble on them pretty regularly, the tubes are holding up well.
You can find this on Amazon. You can buy them individually or in bulk to save money: