Does your guinea pig have enough insulation in his cage for the winter? Even if you have your house heated to a nice 70 degrees F your guinea pig may still be a little cool in his cage. If you see your guinea pig shivering, add bedding for him to burrow in. You may want to drape a towel over part of his cage at night to help lock in heat. If your guinea pig continues to shiver you should call your vet as your guinea pig could be ill. Keeping your guinea pig supplied with timothy hay can help keep him warm as well. He may use it for extra bedding or snack on it all night. Eating hay constantly can help keep him warm. If your guinea pig doesn’t appear to be drinking a lot try giving him slightly heated water. If this doesn’t work ask your veterinary clinic Castle Hills, TX for suggestions.