The present study was conducted to determine chemicalcomposition and truly absorbed protein in the small intestine (DVE) content of alfalfa hay sampled during different stage of the plant maturation. Samples of alfalfa hay were taken at initial, half and full bloom stages, then dried at 65 oC 48 h, using air forced oven, then analyzed to determine crud protein, neutral detergent fiber and acid detergent fiber. Ruminal incubations for test feeds and laboratory techniques were performed according to Protocol for in situ Rumen Incubations published by CentraalVeevoeder Bureau Standards. Truly absorbed protein in the small intestine (DVE) contributed by (1) feed protein escaping rumen degradation, (2)microbial protein synthesized in the rumen and (3) a correction for endogenous protein losses in the digestive tract, the difference between the potential microbial protein synthesis based on rumen degraded feed CP and that based on energy available for microbial fermentation in the rumen (OEB) and fermentable organic matter (FOM) were calculated according to DVE/OEB model. Dry mattercontent of the samples wereincreased with the plant maturation and varied from 260 (g/kg) at the initial bloom to 280 (g/kg) in the full bloom. While, NDF and ADF at the initial bloom were 390,296, at half of bloomwere 430,312 and in full bloom 495, 327, respectively. However, crude proteinwas decreased with the stage of growth and the value for the initial, half and full bloom was 198, 192,190g/kg,respectively. The value of the DVE of the samples was declined with the stage of the blooming and were 162.9,161.3 and 156.1 g/kg for initial, half and full bloom, respectively. The present results indicated that the stage of maturity might impacton the nutritional value of alfalfa hay by altering the chemical composition and especially the protein content evaluated as truly absorbed protein in the small intestine.

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