Have copied this from our diet guide
Pellets
The vast majority of readily available pellet brands is alfalfa based; this needs to be taken into account for an overall diet.
Here is our current UK pellet brand chart:
Nugget Comparison Chart
Please feed pellets and not dry mixes/mueslis, which lead to selective feeding and long term health and teeth problems. Mueslis and dry mixes have now being scientifically proven to be detrimental to rabbit health if fed long term; while there is no comparable study for guinea pigs, the same can be assumed for them.
Pellets Or Muesli / Dry Mix?
Pellets and shop treats often account for overweight, so do not be too generous. If you suspect overweight, reduce the amount of pellets and stop any treats. Don’t do it in one fell swoop, though, or you will have a riot on your hands! Overweight guinea pigs are at a higher risk in operations as well as in the development of long term health issues, so by spoiling your piggies with food – as tempting as it is – you are doing them no favour!
It is also often better to feed a limited amount of pellets and veg in as many bowls as you have guinea pigs, ideally a couple of times in a day, so pellets and veg are eaten in one go (about half to one handful per serving per piggy, i.e. 10-20g). This means that all your pigs have an equal chance at eating their allotted portion, you are less likely to have a greedy hogger/overweight problem, the pellet bowl doesn't get peed/pooed in or attract mice etc. as you can remove the bowls in between meals. As unlimited hay is making the bulk of the diet, your guinea pigs won't go hungry in the meantime and can concentrate on what they should be eating most!
The Importance Of Weighing - Ideal Weight / Overweight / Underweight
Fast growing young guinea pigs up to 4-6 months old
Ca. 40g (just over 1 oz) pellets in order to account for the slightly raised need of more calcium, protein and vitamin C. Please be aware that the extra amounts needed are in fact very small and that they are fully covered by our recommendation.
It is advisable to feed pellets in smaller portions more than once daily rather than just topping up a big bowl. Young piggies often pee (and poo) into the bowl, so you want to empty and clean it daily. If one your piggies is very greedy or dominant, you may want feed smaller portions in bowls that are spaced at least a body length apart.
Slow growing sub-adults between ca. 4-12 months old
Once the weekly weight gain slows down and stops, you can very gradually reduce the amount of pellets you are feeding accordingly until your guinea pigs have reached adulthood.
Fully grown mature guinea pigs over 12-15 months
1 tablespoon of pellets per piggy per day is all that is needed to keep your piggies trim and healthy!
A healthy adult weight is between 800-1500g depending on the individual size; the average weight for fully grown pet piggies at the peak of their lives at 2-3 years old seems to be about 900-1300g.
The Importance Of Weighing - Ideal Weight / Overweight / Underweight
Ideally, you try to aim at 1000-1200g, keeping in mind that the individual variance in guinea pigs is very large and that the ideal range will cover only about 75% of all piggies. So please don't panic if a piggy is naturally larger or smaller; it can still be perfectly healthy and live a normal happy long life!
Older guinea pigs (4 years plus) tend to slowly lose the condition of their prime (2-3 years) and become a bit more bonier. You still need to check with your vet that there is no underlying treatable problem and you need to see a vet quickly if any weight loss is sudden and large (over 2 oz/50g).
Experienced owners measure their piggies' ideal adult size less in weight than in heft. A healthy piggy should have a ribcage that can still be felt, but where not every single rib is standing out. If you can't feel any ribs at all, then your piggy is likely overweight and you may want to reduce the pellet intake and cut down severely on any treats or cut any fatty/sweet treats out completely.
The individual body shape, especially in sows, can vary a lot, so a big bum end is not necessarily a sign of overweight.
