1. Official Methods of Analysis;AOAC,2000
2. Control of digestion and extent of protein degradation;Broderick,1991
3. Modified reagents for determination of urea and ammonia;Chaney;Clin. Chem.,1962
4. Nutritive Values of Seasonal Ranges. Bull 472;Cook,1968
5. Feeds and Nutrition;Ensminger,1990