The inclusion of fruits and vegetables in the diet has been suspected to prevent cancer and the use of natural compounds, or nutraceuticals, to treat the disease has recently been entertained. While there is ongoing research in the use of nutraceuticals to treat a variety of human cancers, little work has been completed in our companion animals, specifically dogs. A screening of feed ingredients deemed safe and reliable by the Association of American Feed Control Officials was performed. After examination of cellular proliferation, apoptosis by flow cytometry, and a multitude of signaling pathways by western immunoblotting, turmeric root and rosemary leaf extracts were determined to be potent inhibitors of neoplastic cell growth. These extracts worked synergistically to induce apoptosis in vitro in canine mastocytoma, mammary carcinoma, and osteosarcoma. These results need further in vivo and clinical examination, as a dietary supplement to cancer treatment could prove efficacious.