This is all I could find. Hope this is both accurate and enough.
Fermentative Digestion in the Stomach of Hippopotamus amphibius (Artiodactyla : Suiformes) and Associated Ciliate Protozoa
JUNE P. THURSTON, CÉCILE NOIROT-TIMOTHÉE & PAMELA ARMAN
Department of Zoology, Makerere University College, Kampala, Uganda.
Laboratoire de Zoologie, Faculté des Sciences, Dijon, France.
Department of Soil Sciences and Agricultural Chemistry, Makerere University College, Kampala, Uganda.
No mammals secrete a cellulase and therefore herbivorous mammals rely on their association with cellulolytic microorganisms to utilize their foods fully. Carbohydrates are fermented in regions of the digestive tract where a large bulk of food is retained for a considerable period of time and where micro-organisms occur. The chief products of fermentation are volatile fatty acids, carbon dioxide and methane. The volatile fatty acids are an important energy source for the herbivore.
Also Hippophobia means fear of horses. Not Hippos.