The interest in agriculture automation is led by energy requirements. Automatic Feeding Systems (AFSs), considering that they are powered by electricity, decrease the use of fossil fuels in farms. We performed a Life Cycle Assessment (LCA), comparing three specialized dairy cattle farms. This study involved a precision agriculture farm (PAF) and two conventional farms (CF1 and CF2), implying three LCA categories: climate change, fossil depletion and non-renewable energy use. The concern about global warming, the need to reduce fossil fuel consumption, and the lack of research focused on fossil depletion in livestock systems influenced our study. We estimated the sustainability of the main product, i.e. the functional unit (FU) in LCA, the milk. PFA showed the lowest values (P < 0.05) of oil equivalents (fossil depletion) and MJ (non-renewable energy use), in comparison with conventional farms (CF1 and CF2). All the farm operations were considered within the system boundaries, including agricultural field procedures and off-farm purchased inputs. Milking is performed by parlor in conventional farms, while in PAF it is performed by Automatic Milking System (AMS). In PAF, the AFS fed all animals, and the manure is partially managed with automatic scrapers. In conventional farms, diesel ensures all the procedures of feeding and manure management; in PAF manure is managed with diesel and electricity. PAF electricity requirements are larger than CF ones; however, they could be provided by renewables, which are lacking in all farms.