Function?

Vitamin C plays a crucial role in supporting a dog's immune system, collagen production, and overall health. While dogs naturally produce vitamin C in their bodies, certain situations might increase their need for it, such as stress, illness, or certain medical conditions. In such cases, providing additional vitamin C through dietary sources or supplements might be beneficial.

Whole food sources?

Apples, berries (blueberries, strawberries, raspberries, and cranberries), broccoli, and green peppers.