Guinea pig is abnormally thin and has trouble standing on its hind legs
Expert Answer
A guinea pig standing abnormally on its hind legs may be caused by malnutrition, or it may be due to a skeletal problem. Based on your description, the guinea pig is abnormally thin, which suggests a likely case of malnutrition. When a guinea pig’s body lacks vitamin C, this kind of condition may appear.
In this situation, pay attention to providing the guinea pig with more nutrition, especially supplementing vitamin C. To further confirm the cause, it is recommended to take the guinea pig to a veterinary hospital for a professional examination.
My guinea pig went thin and weak-legged from a vitamin C deficiency, and daily bell pepper plus C-fortified pellets turned him around. They can't make their own C, so lack causes joint and leg trouble fast. If he's losing weight and struggling to stand, boost C and get a vet check, because scurvy in pigs escalates and other diseases mimic it. Fresh veg daily is the prevention, don't rely on pellets alone.