[Utilization of urea infused into the abomasum in growing lambs]

Effects of partial or full replacement of soybean meal with urea or coated urea on intake, performance, and plasma urea concentrations in lactating dairy cows

We expected mitigation of the hypophagic effects of urea (U) with a coated urea (CU) product that aimed to partially shift urea supply to the post-ruminal gastrointestinal tract. Ruminal release and post-ruminal digestibility of CU was evaluated in vitro, followed by a randomised complete block experiment (54 Holstein-Friesian cows; 177 ± 72 days in milk). Soybean meal (SBM) was partially (PR) or fully (FR) replaced on an isonitrogenous basis by beet pulp and U or CU. Urea sources were included at 12 (U-PR, CU-PR) and 19 (U-FR, CU-FR) g/kg dietary dry matter (DM). Hypophagic effects were similar for U-PR and CU-PR (-11% vs. -7%), and for U-FR and CU-FR (-13% vs. -12%) compared with SBM (average 25.8 kg DM intake/d). Compared with SBM, U-PR and CU-PR reduced yields of milk (-8%) and protein (-12%), U-PR reduced yield of fat (-9%) and fat- and protein-corrected-milk (FPCM; -9%), and CU-PR tended to reduce FPCM yield (-5%). Compared with SBM, U-FR and CU-FR respectively reduced yields of milk (-21%, -22%), protein (-25%, -26%), fat (both -14%), lactose (-20%, -21%), and FPCM (-17%, -19%), and lowered N (-15%, -12%) and feed (-8%, trend, -9%) efficiency. Human-edible protein efficiency approximately doubled with U-PR and CU-PR and approximately tripled with U-FR and CU-FR compared with SBM. Milk composition and plasma urea concentration were similar between U and CU, except for a trend for a greater plasma urea concentration with U-PR compared with CU-PR. Dry matter intake patterns differed for CU-PR compared with U-PR and for CU-FR compared with U-FR, suggesting effects of urea release rate or location on feeding behaviour. Overall, replacing SBM with U or CU reduced DM intake and milk production and affected nutrient efficiencies. Coated urea influenced DM intake pattern but did not affect total DM intake or milk production compared with U.

[Nitrogen and mineral metabolism of growing lambs fed straw treated in different ways]

Lambs were fed diets containing 500 g straw, 50 g sucrose and 30 g minerals per day. The straw was untreated (A), wafered after addition of NaOH (B) or gassed with ammonia. Diets A and B, in addition contained urea, so that equal amounts of dietary N were offered. Digestibility of OM was increased by 12 units after addition of NaOH and by 8 units after gassing with NH3. As significantly more faecal N was excreted in animals fed diet C, it is concluded that N of NH3-treated straw is less available than of added urea. When NaOH-treated straw was fed, renal excretion of phosphorus was increased.