REFINING NITROGEN FEEDING USING CURRENT KNOWLEDGE OF RECYCLED UREA AND MICROBIAL NITROGEN UPTAKE

摘要

Nitrogen efficiency has been a popular topic in the dairy industry in the last few years due to a desire for reduced excretions. Beside groundwater contamination, NH3 and nitrous oxides are able to volatilize and form precipitates, acidify precipitation, and decrease ozone, which in turn is detrimental to human and environmental health. As responsible stewards, many dairy producers and nutritionists have taken strides toward eliminating excess N inputs. Work at Cornell is focused on aiding in this process, and much work is being done to understand enhancements in N efficiency in an effort to reduce N excretion and promote greater milk protein exported from the farm. One step is to better understand, and quantitatively describe, urea-N recycling intothe gastrointestinal tract (GIT) and its utilization by microbial populations. This process allows seemingly excess N absorbed from the GIT and converted to urea to re-enter the GIT for the purpose of incorporation into microbial protein. Current research has shown that approximately 15-40% of N intake may follow this process, so it is important to describe this accurately for nutritional estimates (Lapierre et al. 2004; Ouellet et al. 2004; Valkeners et al. 2007). Further, enhancements of field usablemodels like the CNCPS (Tylutki et al. 2008) and CPM Dairy (Boston et al., 2000) require quantitative data to enhance the predictions from the rumen submodel. If we are going to refine the models, then data supporting more of the dynamics of N utilization, including the incorporation of the protozoa are needed to better predict energy and amino acid yields from organic matter intake.