The impact of lower gut nitrogen supply on nitrogen balance and urea kinetics in growing pigs fed a valine-limiting diet.

An N-balance and isotope dilution study was performed to determine the effect of lower gut N supply on N retention and CO(NH(2))(2) kinetics in growing pigs. Nine cecally cannulated and jugular-catheterized barrows (initial BW 22.4 ± 1.2 kg) were randomly assigned to 1 of 3 cecal N infusion treatments: saline, casein, or CO(NH(2))(2); the latter 2 treatments were infused at a rate of 40% of daily N intake. All pigs were fed a Val-limiting corn (Zea mays) starch and soybean (Glycine max) meal-based diet. Cecal N infusions did not affect apparent total tract digestibility of N (P > 0.05). The efficiency of using N [% of apparent ileal digestible intake; 72.9 ± 1.9, 84.9 ± 1.9, and 85.6 ± 2.3% (P = 0.01) for saline, casein, and CO(NH(2))(2), respectively] and Val (76.9 ± 1.9, 86.5 ± 1.9, and 86.5 ± 2.4; P = 0.02) for whole body protein and Val retention increased for casein and CO(NH(2))(2). Urea flux and urinary N excretion increased (P < 0.05) similarly for both N infusions, but this increase did not fully account for lower gut N disappearance. Lower gut N disappearance is in the form of NPN, which can be used for microbial AA production in the upper gut and should be considered when determining N and AA supply and requirements.