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Technical Abstract: Forages contribute absorbed protein to the dairy cow by providing crude protein that is degraded by ruminal microbes to nonprotein N (NPN), that is in turn used to form new protein, and by providing protein that escapes microbial breakdown in the rumen (bypass protein). Inefficient utilization of forage crude protein, particularly the high amounts of NPN in alfalfa silage, and the over feeding of protein that this necessitates, leads to excessive N losses to the environment from dairy farms. Efficiency of N utilization from grazed forages also is poor. Alfalfa silage contained more than half of its total crude protein in the form of NPN; this was true in alfalfa silage harvested under experimental conditions and on commercial dairy farms. Reducing NPN content of alfalfa silage by one-third improved milk yield by 3.4 kg/day and protein yield by 120 g/day when fed to lactating cows. Practical methods for reducing NPN in alfalfa silage currently are lacking. Certain forages such as red clover give rise to silage with reduced NPN; although promising, red clover silage has not yet proven to be an effective substitute for alfalfa silage. Genetic selection also holds promise for reducing ruminal degradability of alfalfa protein. Feeding more finely ground concentrate, when adequate effective fiber also was fed, maximized utilization of silage NPN for ruminal protein formation and improved milk and protein yield. Lower NPN content of alfalfa hay, and possibly its slower rate of protein degradation, increased efficiency of ruminal protein formation compared to alfalfa silage. Improved farm equipment may make hay harvesting a more practical alternative to silage harvesting in the future.