Livestock grazing systems constitute a traditional activity in mountain areas. They are adapted to vegetation growth cycles in meadows, forests and grasslands, and deliver ecosystem services such as open landscapes, wildfires prevention, biodiversity maintenance and quality products. Climate change poses a new challenge on mountain grazing systems by impacting on its natural resource base. We used the model NODRIZA to evaluate the potential impact of three scenarios of altered pasture quality and quantity due to climate change (optimistic, medium and worst) and a business-as-usual scenario (BAU) on four beef farms representative of the existing grazing systems in the Spanish Pyrenees. We explored the role of traditional management practices (e.g. modifying the grazing season and early weaning) to cope with these changes. Cow body condition score, feed self-sufficiency and gross margin were the indicators of farms functioning. The optimistic scenario improved all farming indicators during most of the modelled period and then declined—still above BAU levels—in the long term. The medium scenario resulted in an initial improvement of farming indicators and a decline to BAU levels in the long run. The worst scenario declined all indicators below BAU levels. The four case studies were impacted in the same direction but to different extent, farms oriented to fattened calves suffered higher impacts than those focused on weaned calves. Traditional adaptation actions succeeded to maintain cow body condition score steady, but they came at the expense of lower feed self-sufficiency and gross margin, becoming impractical to face climate change.