Guinea pig feet and nails + cage floor

Question
My guinea pig cage has a metal floor, with a tray underneath that catches all their mess. I am concerned that this may hurt their feet, walking on this type of surface because it does not have anywhere flat to step on. They have been in this cage for a few months; they were babies not too long before that and i had them in a huge woodchip-filled tupperwear container. they loved it in there, but i find the tray much easier and convenient to clean. i am just concerned about their feet, and if the metal could hurt them over time.

also, how often should their nails be trimmed?  

Answer
Yes over time the cage with the wire floor bottom can and will hurt their feet. This really isn't the best cage method, but people do do it anyways. There is a condition that can come from a pig being housed this way. It is called "bumblefoot." "Bumblefoot" is when the feet get extremely red, sometimes pussy and sore. It can irritate them so bad they bleed from it and get painful sores. I know it is soooooooooo much easier to clean the wire caged bottoms that are meant for a rabbit. I mean litterally it takes less than 5 minutes, but in the end it does make the pig suffer. Guinea pigs have smaller feet than a rabbit does, so sometimes they just slip right through. A couple reccomendations are to put a piece of sturdy cardboard or linoleum on half of the cage so they can some how relax. Imagine wearing high heels on a sewer grate. Your feet would constantly get stuck. Another possibility is to get another cage entirely. I have fairly large cages for each of my pigs, and I just pick up the entire plastic cage bottom, and dump it in a 30 gallon trash bag. It does wonders, and it makes the job go really fast. I can't tell you what to do, so I'll have to leave the final decision on what you do with your pigs up to you. Their nails should be trimmed every few weeks, or how I go by it, is when they're painfully digging into me. Make sure they don't become too long. A rescue pig I have unfortunately has terribly curly deformed nails, even when they are cut short. He walks very awkwardly. This is result of them not being cut BEFORE they became a problem. The nails can actually curl back  up into your pigs foot. Make a fist keeping your thumbs standing straight up. That's what can happen. If you have any more questions feel free to ask me :) I wish you and your pigs a lifetime of health, happiness, and love. :)