We don't go to shetland shows yet, but do like to go to local open shows. I still like to present my ponies as if it were Congress though. I have three ponies that I'm conditioning right now, 2 mares and a filly, and they each need different amounts of feeding and conditioning. And I'm always tweaking our program a bit to adjust to what each one might need.
We feed Purina complete diets (the mares get Equine Sr., the filly gets Adult or Sr., depending on her condition), Purina Mare & Maintenance, Black Oil Sunflower Seed and soaked Beet Pulp with a bit of bran or oats to balance the Ca
hos. They get very little hay, maybe a small handful of alfalfa if they look 'munchy' or bored. They generally would get turn out on sparse pasture as well, but have been kept in the barn or on dry lot for the last couple of months (that's a whole 'nuther thread). This diet is more in response to a string of colics I had a while back than to conditioning, but I'm more interested in keeping their guts moving than anything else at this point.
As far as amounts go, mine vary so much between the ponies that it probably wouldn't be much help. My 41" mare needs twice as much feed as my 40" mare. When she's conditioning, she gets nearly as much as my big horses at rest (she's a really hard worker). I originally cut the filly back, because she came out of winter/spring fat, but now I'm gradually increasing her feed as I increase her work. But here's how I determine where to start. Read the guidelines on the back of the bag. Find out the weight capacity of whatever feed scoop you are going to use for each feed. I have it written on the trash cans that I store my feed in. "1 red scoop = 3 lbs." It varies from feed to feed. Also, Purina dealers or your vet should be able to give you a body conditioning score chart (or ask the vet to score her next time he's out). That will give you a good idea where you are starting. Then you can determine where you want to go, and just make little adjustments. I'm always evaluating my ponies and my feed program, and can even alter it in small amounts every few days sometimes. It makes hubby (my helper) nuts sometimes.
For conditioning my mares, in normal years we lunge at good working paces for 20 +/- minutes every-other-day. This includes trot poles and little 'pop over' jumps occasionally. I call it 'cardio day' or 'sweat day'. This year I'm hurt, so have been doing a lot more free lunging. On the non-lunge days, we do long, brisk walks (up to 2 miles/day, with breaks to chat with the neighbors). Right now it's just in a halter, or the lead-line pony might wear her tack. When I'm healed, this will be ground-driving or driving. These are also the days we practice in-hand exercises or new things; 'tech day' we call it, lol.
For my 2 year old filly, right now we are just trying to figure out a way to work her without hurting me. She's just sooooo TWO. Busy, busy, busy. Lots of free-lunging and long walks. But she's bored, so I'm going to have to step it up a bit. I started her on the lunge line this week, and she hasn't yanked me around too much. We are going to introduce her to the bitting rig and hopefully in a another few weeks I can start ground driving her a bit. Ugggghhhh.... she's just so two!