The Comparison of the Main Protein Sources for Dairy Cows. a Review

YILDIZ, E. and N. TODOROV, 2014. The comparison of the main protein sources for dairy cows. A review. Bulg. J. Agric. Sci., 20: 428-446 Review of now-a-day knowledge was made for nutritive value and effect on milk yield and composition of the main protein sources – soybean meal (SBM), sunflower meal (SFM), rapeseed (canola) meal (RSM), and dried distillers grain with solubles (DDGS) – in diets of dairy cows. Independent of low lysine content of DDGS and RSM and some inconsistent data, there are many group production experiment with dairy cows showing equal or even higher milk and protein yield, compare to rations with SBM. There is limited number of published experiments to compare SFM with SBM, but in part of them there are not significant differences in milk production and composition, while in other trials SBM have advantage. In spite of significant differences in rumen degradability, intestinal digestibility of rumen undegadable protein, and amino acid composition of different protein sources in many trials milk and protein production is not corresponding to nutritive characteristics. Authors are mentioning several suggestions to explain discrepancies between theoretical requirement of cows for rumen undegradable protein and for lysine and experimental production results which are supported in some experiment, but scientific evidences are not enough so far. It is emphasized needs of further experiment to compare SFM with other protein sources, and to find biologically and economically optimal combination of different protein sources in ration of dairy cows, especially for region of Shout East Europe.