Milk Urea Content and δ13C as Potential Tool for Differentiation of Milk from Organic and Conventional Low- and High-Input Farming Systems

The influence of farming type (conventional or organic) and production system (low-and high-input) on various quality characteristics of milk have been in the focus of studies over the last decade. The aim of this work was to evaluate the impact of different dairy management and production systems on carbon stable isotopes ratio (δ13C) and milk urea content. The samples of raw milk were collected each two weeks at certified organic high-input and low-input farms, conventional high-input and low-input farms in late indoor period and outdoor period. Data analysis showed clear difference between milk from organic high- and low-input farms with non-overlapping range between -22.90 ‰ and -24.70‰ for δ13С in protein fraction (equal 1.80‰) and between -25.90‰ and -28.20‰ (equal 2.30‰) for δ13С in fat fraction independently from season factor, as for Δδ13С (protein-fat) values in milk from high-input (1.50-3.00‰) and low-input (3.20-6.30‰) organic farms. Analysis of correlation between δ13С in protein fraction and milk urea content values showed that during late indoor period the most significant difference was detected between milk from organic low-input and conventional high-input farms (5.85‰ for δ13С in protein fraction and 4.65 mg/100 g of milk urea content). During outdoor period, the non-overlapping range was established for low-input and high-input organic farms (3.40‰ for δ13С in protein fraction and 10.77 mg/100 g of milk urea content). Results of δ13С values in fat and protein milk fractions, as combination of δ13С in protein fraction and milk urea content could be a potential tool for the distinguish of milk from different farming types, based on different feed composition.