These include age related changes in enzyme activities as well as inherent species differences in metabolic pathways. (en.wikivet.net)
While we still know relatively little about age related changes in our pets, there are some strategies that help. (dallasmetropaws.com)
Older pets may have age - related changes of the nasal membranes that make infections worse and their immune systems may not be as vigorous as they once were. (2ndchance.info)