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We can only control what we can measure. In the case of dairy farming, nitrogen utilisation requires a higher level of control to reduce environmental pollution and improve farm economics. Nitrogen metabolism in the ruminant animal is a complicated system and accurate evaluation of protein utilisation by dairy cows is limited by current methods. This dissertation assesses various methods of analysing ruminal crude protein degradation and introduces a new method of assessing protein value of forages i.e. the protein available to the ruminant for absorption at the duodenum. The following procedures are included: in situ incubation, Cornell Net Carbohydrate and Protein System, in vitro enzymatic degradation and the modified Hohenheim gas test. The third section of this dissertation applies these methods to a controlled experiment investigating the effect of wilting on the protein value, protein characteristics and amino acid profile of grass silage. Conclusively, the results of this study aid in estimating protein supply from forages to dairy cows.

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Bronwyn Edmunds Dr.Ag.Sci.: Born in Australia (1982). Bachelor with Honours in Animal Science, University of Western Australia (2004). PhD in Agricultural Science, specialised in ruminant nutrition, University of Bonn (2011). Will return to Australia in 2012 to continue her career as an animal nutritionist.

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