Unless you weigh your guinea pigs fairly regularly then it can be really difficult to check for changes in weight. Weight loss or gain can be an indication of a health problem, and it can be one of only a few symptoms. The weights of your guinea pigs will change a little throughout the year, but dramatic weight loss can merit a trip to the vet. Weights vary a lot because there are big physiological differences between individuals and breeds. For example, Rex guinea pigs will often be a little larger than some of their friends.

Weights go up and down a little throughout the day
Once you’ve established your guinea pigs’ base weights, then guidelines are as follows:
If your guinea pig weighs less than about forty or fifty grams less than the last weigh in, this can just be part of normal fluctuations.
If your guinea pig weighs more than fifty grams less than the last weigh in, then weigh them each day and give them some more dry food just in case.
If your guinea pig weighs around one hundred grams less than the last weigh in, then this is very serious, and implies there is something seriously wrong. If this has been happening over a long period, then it’s still cause for concern, and your pet will need to see a vet immediately.
Foods For Weight Gain
If your guinea pig hasn’t been well and needs a bit of TLC, then we recommend giving them a little more dry food than usual, a little more hay, and offering them some carrots and corn which are good, dense foods for your pet.
Grace, 24 February 2020
Hi, my guinea pig is 4 years old. I noticed that she has suddenly losing a lot of weight. She used to be a REALLY chubby guinea pig but lately i am able to feel her hip bones and her ribs. I have been trying to give her foods like carrots now, so she will gain some weight but if it gets any worse i will take her to the vet. Not to mission that i am younger than 13 so i will need some help from my family.