Their nails can get really long and have to be kept trimmed otherwise they can start to curl inwards and cause a lot of discomfort. If your piggies have white or clear nails this is quite easy as you can see where the little blood vessel in the nail is and trim the nail back to that. You should be careful not to cut this vessel as it will bleed a fair bit (I have done it before!) However if their nails are dark it's not so easy and is a matter of guesswork really. I have some special clippers and with my pig who has dark nails I just trim off the pointy bit so that his nails are not too sharp. If in doubt a nurse at your vets should be able to show you how to do it.