If they are not eating enough hay, their digestive system may actually shut down. (petconsider.com)
Too many carbohydrate - laden pellets and not enough hay can alter the GI bacteria and lead to GI tract slow down. (avianexoticsvet.com)
Even if they are not as high in sugar or starch as fruits and other treats, they can still cause digestive problems if your rabbit isn't getting enough hay. (petconsider.com)