It has been discovered that Red Osier Dogwood can be fed to domesticated animals such as livestock as part of a feeding regimen in place of silage. Surprisingly, the Red Osier Dogwood results in increased growth compared to a control fed a regular diet. Experiments have shown that the Red Osier Dogwood is rich in antioxidants such as rutin, gallic acid, ellagic acid, quercetin and tyrosol. Also described herein are methods of preparing extracts from Red Osier Dogwood comprising high levels of these antioxidants, which can be used in the preparation of medicaments for the administration to animals, including humans.