Dairy manure protein analysis using UV-vis based on the Bradford method

Abstract

Organic nitrogen in the form of protein and degraded protein fragments is one of the most important components of dairy manure. Conventionally, protein concentration in dairy manure was estimated by crude protein but it is often overestimated because crude protein contains non-protein nitrogen (NPN). The Bradford assay is predominantly used in measuring clinic samples. In this paper, dairy manure protein assays including the Bradford assay, total Kjeldahl nitrogen method and amino acid analysis were compared using various types of manure samples with a wide range of solids contents at different on-farm treatment steps. The manure protein concentration assay by UV-vis using Bradford method was validated to be compatible to measure the protein concentration in manure samples. Relationships for estimating manure total protein concentration from soluble protein based on the solids contents have been determined. The method described in this study could be used as a supplement method for traditional protein assay, especially when the solids content in manure samples is low. In addition, this method can be easily adapted at a farm level to monitor manure soluble protein and estimate crude protein concentration in order to evaluate the effects of diet change and to manage manure field application amount as fertilizer.