Please have your piggy vet checked. This kind of intensely red coloured urine (porphyrines, not blood) is typical for the onset of a urine infection or cystitis. Symptoms are usually not consistent at the very onset, but the sooner you can start treatment, the less uncomfortable it is going to be for your piggy. At this early stage not all pees contain blood (which can present in surprising quantities in still clear pees) and not all pees will contain porphyrines.
Please follow our diet recommendations; including filtering water, the amount and quality of pellets you feed and the calcium content of the diet (which needs to be carefully balanced) to minimise the risk of long term problems.
Long Term Balanced General And Special Needs Guinea Pig Diets
If your guinea pigs are still living outdoors, please consider bringing them indoors or under cover for the winter. Guinea pigs don't deal well with major short term temperature swings, and we have had nights with temperatures coming close to frosts as well as warm days in very quick succession lately.
Cold Weather Care For Guinea Pigs
Hot weather management and heat strokes