Managing and treating elevated OS biomarkers in mammals such as companion animals with at least one of the supplements alpha-lipoic acid, carnitine, co-enzyme Q-10, ginger, green tea, licorice, milk thistle, garlic, honey. resveratrol, soybeans, tomatoes, turmeric, vitamin D, vitamin E, or selenium. Other compounds are Zinc, Vitamin E, Vitamin C, Quercetin, L-glutamine and Robuvit. Diagnosing an oxidative stress (OS) in a mammal detects an OS biomarker, selectively isoprostane and other antioxidant biomarkers such as HODE, microRNAs, TAC, GSH, MDA, and TNF-alpha. The sample can be saliva.