alvine means 'Designating an excretion from the intestines or (rarely) other organ of the belly. Also: designating the intestinal tract; of or relating to the intestinal tract' see: https://www.lexico.com/definition/alvine
and intestines can be defined as 'the lower part of the alimentary canal from the end of the stomach to the anus 'https:/' https://www.lexico.com/definition/intestine
so I would say 'bowel movement' is an acceptable translation