Guinea pigs cannot produce vitamin C in their bodies and need a fresh supply in the diet every day. Good sources are green leafy vegetables, fresh and dried grass, fruit and specially supplemented pellets or mixes sold for guinea pigs.
Guinea pigs are obligate herbivores, eating only plant material. Their natural diet consists of grasses and other plant material. Although there are many very pretty looking guinea pig mixes on the market, you need to know that they consist a mixture of different ingredients that are not well balanced foods for guinea pigs individually, but when eaten together form a balanced meal. If the guinea pig selects only one type of ingredient within the mix and feeds exclusively on that, it is a bit like us eating only meat or only potatoes or only broccoli. When guinea pigs are kept together, which is often the case, a ‘Jack Spratt and his wife’ situation can develop.
Too many guinea pig foods on the market have more protein than fibre so it is good to find a grass and herb based pellet for guinea pigs with the proper level of fibre and high fibre to protein ratio.
A good pellet is grass based, smells sweet and looks green. One well known complete extruded ‘pellet’ food for guinea pigs includes fishmeal in its ingredients, presumably in an attempt to achieve a higher protein level in the analysis, which I suppose would be fine if we fed them fish and they ate it, but I haven’t come across a fish eating guinea pig yet. The only time I have heard of fishmeal being used in guinea pig diets is in South America where they are a local delicacy and being fattened up for the table..
The use of grains in extruded biscuits means the fibre levels have to be obtained from other sources and, as with some pellets used in mixes, this can come from straw treated with urea. If feeding a manufactured diet you should check the list of ingredients. I prefer feeds which list actual ingredients rather than hiding behind loose terms like ‘of plant or animal origin’!
Although it has not been scientifically proven, there was a time when the Cambridge Cavy Trust had significant numbers of guinea pigs being brought to them, all on a well known commercial guinea pig mix and all with the same symptoms that were a cross between urinary tract and diabetes. When transferred to a diet of grass and goat mix these animals improved. They also did well on the same company’s rabbit mix that was free from artificial colouring, and their symptoms returned if they went back on their original diet with the artificially coloured biscuits in it.
As their natural diet is grass, it makes sense to keep them on it. They need the long indigestible fibre in grass and hay for their digestive system and to keep their continually growing teeth ground down to a normal length. They can live quite happily on a diet of good quality hay, pure dried grass, wild plants and herbs and vegetables. Good quality hayshould be available even if feeding mix or pellets.
Good foods for guinea pigs include the outside leaves of cauliflower (but not the white ‘flower’), split the stem of the leaf down the middle; stems of broccoli chopped into quarters lengthways are also enjoyed although they have little nutritional value; broccoli flowers, green or black cabbage, kale, chicory, carrots, parsnips, sweet corn outer leaves and the silk (sweet corn is fattening and overheating but makes a good winter food), raw beetroot, celery, cucumber, small amounts of parsley, small amounts of apple although it can cause mouth sores in susceptible animals; wild plants including plantain, golden rod, cleavers, yarrow and dandelion in a balanced salad – dandelion is a diuretic and can make their droppings soft if fed to excess.