Comparison of Urea and Biuret as Nitrogen Supplements to Low-quality Forage: Daily and Alternate Day Supplementation

An experiment was conducted to determine the influence of supplemental non-protein N (NPN) provided daily (D) or every-other-day (2D) on nutrient intake and N efficiency in lambs.  Treatments included an unsupplemented control (CON) and a urea (28.7% CP) or biuret (28.6% CP) supplement provided D or 2D at 0700. Five wethers (39 ± 1 kg BW) were used in an incomplete 5 × 4 Latin square with four 24-d periods to determine the influence of supplemental NPN source and supplementation frequency (SF) on efficiency of N use in lambs consuming low-quality grass straw (4% CP).  The amount of CP supplied by each supplement was approximately 0.10% of BW/d (averaged over a 2-d period).  The supplemented treatments received the same amount of supplemental N over a 2-d period; therefore, the 2D treatments received double the quantity of supplemental N on their respective supplementation day compared with D treatments.  Total DM, OM, and N intake, and DM, OM, and N digestibility, N balance, and digested N retained were greater (P < 0.03) for supplemented wethers compared with CON with no difference (P > 0.05) because of NPN source or SF.  Plasma urea-N (PUN) was increased with N supplementation compared with CON (P < 0.01) and urea treatments had greater PUN compared with biuret (P < 0.01).  Also, PUN was increased (P = 0.02) for D compared with 2D treatments.  In addition, PUN appeared to exhibit less fluctuation on the day of a supplementation event for biuret compared with urea.  These results suggest that supplements containing urea or biuret as the primary source of supplemental N can be effectively used by lambs consuming low-quality forage, even when provided every-other-day.

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Currier, T.A., D.W. Bohnert, S.J. Falck, and S.J. Bartle. 2004. Daily and alternate day supplementation of urea or biuret to ruminants consuming low-quality forage: Effects on cow performance and efficienty of nitrogen use in wethers. J. Anim. Sci. 82:1508-1517  (DWB PDF#2)