In this experiment the effects of different urea products (urea, Paraffin-sulfur Coated Urea (PSCU) and controlled release urea product (Optigen, Alltech Inc., Lexington, KY)) on rumen fermentation were investigated in dependence of different diet sources by using in vitro techniques. The experiment followed a completely randomized design using four N-source treatmentes (urea, Paraffin-sulfur Coated Urea, Optigen and canola meal) in four diets (wheat straw+ %3 isonitrogenous of each N-source, barley grain+ %3 isonitrogenous of each N-source, barley grain+ molasses+ %3 isonitrogenous of each N-source and formulated TMR diets for dairy cow+ %3 isonitrogenous), the cumulative gas production (96 hours) influenced by diets and N-source treatments was different, which was higher gas production in formulated TMR diets for dairy cow and least gas production in wheat straw. The result indicated that Optigen (90.82) and then PSCU (90.81) the highest gas producer in the formulated TMR diets for dairy cow and the canola meal (69.04) and urea (69.43) had the least gas production in wheat straw (P<005). As a result, little difference between treatments for slow-release urea with control (canola) was observed in animal experiments. And therefore reducing feed costs and increasing the efficiency of the rumen microorganisms can be used NPN sources as a replacement for part of dietary protein.

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