Evaluation of Biuret as a slowly degradable non-protein nitrogen source for lactating dairy cows.

Our objective was to examine if Biuret (ADM Alliance Nutrition, Inc., Quincy, IL) is a suitable replacement for ruminally degradable true protein in dairy lactation diets. Lactating Holstein cows (n=237) were divided into three groups balanced based upon parity, stage of lactation (DIM), and mean milk production measured one week before the co-variant adjustment period. The standard lactation ration served as the control ration (CT). A 2-week co-variant adjustment period in which CT was fed was followed by a 28-day test period during which cows received diets containing 0, 45 (LO), or 77 (HI) g/cow/day of Biuret. Biuret replaced an equivalent amount of soybean meal-nitrogen in the diet. Urea and total crude protein of diets were similar among diets. Estimated bypass protein content of diets decreased and non-fiber carbohydrate increased with addition of Biuret. Data was analyzed using the Proc Mixed procedure of SAS for a repeated measures, completely randomized design. Milk yield and components were covariant adjusted using data collected in the pre-test period. Substitution of Biuret for ruminally degradable true protein did not affect milk yield (P>0.10). Dry matter intake linearly decreased (P<0.05) with Biuret feeding. Efficiency of milk yield (milk/feed DMI) improved when Biuret was fed. The HI treatment decreased (P<0.05) daily milk fat yield (1371, 1374, 1305 g for CT, LO and HI, respectively) and decreased (P<0.05) milk lactose percentage (4.86%, 4.85%, 4.82% for CT, LO and HI, respectively). Data were parsed into high and low production groups based on pre-study median performance to examine treatment effects of Biuret on milk yield and composition. Milk composition of lower-producing cows was affected by Biuret whereas milk yield was more responsive to Biuret in higher-producing cows. For all cows, MUN levels increased with Biuret feeding. Milk urea nitrogen may be an appropriate tracking variable to evaluate efficiency of nitrogen use when slowly degradable NPN sources, such as Biuret, are fed to lactating dairy cows. In lactating cow diets balanced for RDP and RUP, Biuret was an effective substitute for ruminally degradable true protein. [ABSTRACT FROM AUTHOR]