rates of ruminal, post-ruminal and total tract protein disappearance of the various feeds originating Ruminal, post-ruminal and total tract protein disappearance of various feeds originating from Iranian plant varieties classified as grains (barley and maize), by-products (sugar beet pulp and wheat bran), protein sources (soybean and cottonseed meals), forages [alfalfa hay and maize silages treated with 16 (MS16) or 24 (MS24) g of urea per kg dry matter (DM)] and halophytes (Atriplex sp., Sauda sp. and Kochia sp.) were evaluated using the in situ mobile bag technique, an in vitro enzyme procedure and a three-step in situ/in vitro enzyme procedure. Linear regression equations were determined between results from the mobile bag technique and the two other procedures. Mean ruminal protein disappearance of grains, by-products, protein sources and forages were higher (P < 0.05) than halophytes [0.50, 0.62, 0.54, 0.54 and 0.41 (S.E.M. = 0.05), respectively]. There was an effect (P < 0.05) of feed classification on post-ruminal protein disappearance (grains = 0.63, by-products = 0.52, protein sources = 0.66, forages = 0.43, halophytes = 0.41, S.E.M. = 0.06). Total tract protein disappearance of grains, by-products and protein sources were also higher (P < 0.05) than forages and halophytes (0.81, 0.83, 0.84, 0.74, 0.65, S.E.M. = 0.03, respectively). Procedures did not have an effect (P > 0.05) on from Iranian plant varieties. The best correlationwas observed when results of total tract protein disappearance determined by the in vitro method were plotted against the three-step procedure (r2 = 0.66). The coefficient of determination (r2) for the relationship of total tract protein disappearance between the mobile bag technique and in vitro, and three-step procedures were 0.61 and 0.55, respectively.

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