1. AOAC (2000a) Protein (crude) in animal feed. AOAC-990.03. In: Official methods of analysis of the Association of Official Analytical Chemists, 17th edn. AOAC, Arlington
2. AOAC (2000b) Urea and ammoniacal nitrogen in animal feed. AOAC 941.04. In: Official methods of analysis of the Association of Official Analytical Chemists, 17th edn. AOAC, Arlington
3. AOAC (2000c) Ash of animal feed. AOAC-942.05. In: Official methods of analysis of the Association of Official Analytical Chemists, 17th edn. AOAC, Arlington
4. AOAC (2006) Crude fat in feds, cereal grains and forages. AOAC-2003.05. In: Official methods of analysis of the Association of Official Analytical Chemists, 18th edn. AOAC, Arlington
5. Binford GD, Blackmer AM, El-Hout NM (1990) Tissue test for excess nitrogen during corn production. Agron J 82:124–129. doi: 10.2134/agronj1990.00021962008200010027x