Methods of treating neonatal and young non-human animals suffering from diarrhea, and/or symptoms thereof, by administering to an animal in need thereof a proanthocyanidin polymer composition isolated from a Croton spp. or a Calophyllum spp. are provided. In particular, the neonatal and young animals include calves, young equines and young camels, which frequently suffer from diarrhea of various etiologies, and the administered proanthocyanidin polymer composition is isolated from Croton lechleri. Further provided are methods of improving weight gain and/or reducing mortality in neonatal non-human animals by administration of the proanthocyanidin polymer composition. The composition, either enteric or non-enteric, can be in aqueous soluble form and orally administered to the affected neonatal and young animals.
