Dairy cattle have long been criticised for their impact on the environment, and concern is increasing specifically with regards to the role played by their greenhouse gas (GHG) emissions in global warming (FAO, 2006). While enteric fermentation from ruminants undoubtedly contributes to the emission of GHGs, landfill sites are ranked as the third anthropogenic source of GHG emissions, constituting 11% of all anthropogenic methane emissions (Bogner et al., 2008; Aghdam et al., 2018). Approximately one-third of all food produced globally is wasted each year, with approximately 24% of all products in the landfill being former food (FAO, 2013; USEPA, 2017). While consumer-level food waste remains a problem to be investigated, the use of agro-industrial by-products in dairy rations may provide a sustainable alternative route for products that cannot be consumed by humans but still have a high organic value. Valorization of agro-industrial by-products can minimize the amount of food waste that reaches landfills, subsequently decreasing landfill GHG contributions, while altering the amount of GHG produced by dairy cattle as they turn low-value food-waste into high-value food destined for human consumption. With the increasing threats of global food security and global warming, it is imperative to investigate GHG production profiles when agro-industrial by-products are included in dairy rations, to determine whether overall emissions are reduced and to what extent dairy farmers are contributing to the reduction of the carbon footprint of the dairy industry.