Mushroom wastes are available in high volumes, with 5 million tons of spent mushroom substrate (SMS) being disposed of globally every year. Due to this high availability, various forms of SMS have been researched for their use as alternative animal feeds. Additionally, experimental techniques can be used to grow certain mushroom species, such as oyster mushrooms (Pleurotus sp.) on various lignocellulosic waste materials. Therefore, the SMS from Pleurotus sp. grown on these waste materials may offer a promising conversion from a waste material to a low-cost, nutritionally sufficient feed. However, little research has been done to determine if feeds from Pleurotus SMS specifically grown on urban waste substrates offer the same benefits. Given rising awareness on circularity and urban self-sufficiency, growing mushrooms on urban waste is a promising solution which should be investigated. This paper assesses the feasibility of using SMS from golden oyster mushrooms (Pleurotus citrinopileatus) grown on urban waste as dairy cattle feed, comparing substrate ratios to determine which would result in the most desirable protein and fiber contents. SMS from three experimental substrates of cardboard and spent coffee grounds (SCG) were compared to traditional dairy cattle feeds. Treatments 2 and 3 were found to be suitable for use as additives to traditional feeds in small replacement amounts. However, both treatments also had high fiber content, which may affect practicality of use as feeds.