In vivo total tract nutrients digestibility [Dry matter (DM), Crude protein (CP), Organic matter (OM) and Digestible organic matter in dry matter (DOMD)] from alfalfa hay and barley grain were evaluated using a direct lambs (49.5 ± 3.5 kg, body weight) were fed experimental diets made of four alfalfa hay: barley grain ratio (DM basis) as 1.0:0.0, 0.75:0.25, 0.50: 0.50 and 0.25: 0.75 in a 4×4 repeated Latin squares design. Each period consisted of 28 d with 7 d for feces collection. Nutrient concentrations of feed samples and feces were determined using standard procedures. For direct calculation, the data of first and third diets were used. Simultaneous models were provided using Polynomial regression models of SAS. Apparent DM, CP, OM and OMD digestibility of alfalfa hay and barley grain calculated by direct calculation were 0.61& 0.78, 0.74 & 0.69, 0.64 & 0.80 and 0.59 & 0.79, respectively. When simultaneous models were considered, a linear equation was significant (P< 0.01) for all nutrients. Therefore, the nutrient digestibilities of the feed samples were determined using this model (Table 1). Results of the present study might suggest that the simultaneous models appeared to give reasonable estimate rather than direct calculation.

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