Simple Summary: Transhumance of dairy cows to upland pastures during summer is a tradition in mountain farming systems. Different management systems are practiced in the upland depending on topography and available infrastructures. This study aimed to assess the effects of two traditionally practiced upland pasture management systems (full-time grazing and part-time grazing) on feeding behavior and milk yield and quality. Cows with access to pasture for only 6 h per day had different feeding behaviors than cows on pasture 24 h per day; their milk yields, however, were similar. Although protein and casein contents were higher in the milk of cows with full-time access to pasture, milk coagulation properties did not differ between the two systems. The differences found in milk fatty acid profiles suggest that cows with part-time access to pasture mobilized more body fat reserves to counterbalance the energy expenditures required during fasting periods and for walking back and forth between the barn and the pastures. Abstract: Different grazing management systems are practiced on upland dairy farms during summer, depending on topography, local traditions, and infrastructure. The present experiment compared two distinct management systems with respect to feeding behavior and milk-related properties. Two similar groups of eight Valdostana Red Pied cows originating from two farms were followed during three grazing events in summer on three upland grazing sites. Cows in the full-time grazing group were kept exclusively on pasture and milked twice daily in a mobile milking parlor. Cows in the part-time grazing group had access to pasture for 4 h and 2 h after their morning and evening milkings, respectively. The part-time grazing cows differed markedly in their feeding behavior; they exhibited shorter daily ingestion times and longer durations of ingestion and idling bouts than full-time grazing cows. Part-time grazing cows had lower milk protein and casein contents, but milk yield and milk coagulation properties did not differ from the full-time grazing cows. As a result of the fasting periods in the barn, part-time grazing cows synthesized less fatty acids de novo and mobilized body fat reserves, as evidenced by the higher proportion of oleic acid in their milk fat.