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Delayed cutting during the practical harvesting season of first‐growth forages raised in humid climates has resulted in a linear decline in the digestibility component of nutritive value. This study considered the effect of cutting date upon the digestibility and intake components of nutritive value of first growth alfalfa (Medicago sativa L.) raised under irrigated conditions at two altitudes in Utah and Montana. Duration of the study was 5 years with harvests occurring over ranges of 23 to 62 days. Intake and digestibility by total collection of each hay were determined with four sheep. Digestibility was determined during three years at both ad libitum and a controlled feeding level. Hays were harvested at Huntley, Montana for the first two years and at Logan, Utah for the remaining three years. The variety ‘Ranger’ was used during the first four years and ‘DuPuits’ and ‘Lahontan’ varieties were compared during the last year. Daily intake of dry matter decreased 0.21 g/kg BW¾ for each day of delay with large variations in rate of change for different year‐variety sets of data. Digestibility of the dry matter decreased approximately 0.28 percentage units per day for both Huntley and Logan hays, but Ranger alfalfa was about six percentage units more digestible on June 10 at Huntley than at Logan. Correlations between dry matter and energy digestibilities and between dry matter and organic matter digestibilities were 0.98 and 0.97, respectively. Crude protein concentration declined 0.20 percentage units per day. Digestible protein concentration of alfalfa forage can be expressed as a function of crude protein concentration by Y = −4.15 + 0.97X with r = 0.98.

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