Gangrenous mastitis was managed in a 3-year-old lactating doe by partial mastectomy following unsuccessful medical management. The patient had progressive swelling, hardened and dark discolouration of its left half udder. There was left supra-mammary lymphadenopathy and an open wound at the proximal portion of the affected gland. The right half of the udder appeared normal and was warm to touch. Culture and sensitivity test of a swab sample from the open wound at the base of the affected mammary gland revealed Staphylococcus and Streptococcus species which were sensitive to amoxicillin, cloxicillin, gentamicin and chlortetracycline, but resistant to penicillin and streptomycin. Mastectomy was indicated because of the chronic nature of the disease and the presence of gangrene. The procedure was carried out using a standard sterile technique, and a fenestrated drainage tube was placed. The patient recovered uneventfully and was discharged 14 days post-surgery. The management protocol used in this case demonstrated that unilateral mastectomy with good post-surgical management could be used for effective management of gangrenous mastitis without complications while still preserving the unaffected gland for future lactation.