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Amino acid usage for protein retention, and, consequently, the AA profile of retained protein, is the main factor for determining AA requirements in growing animals. The objective of the present study was to determine the effect of supplementing ammonia N on whole-body N retention and the AA profile of retained protein in growing pigs fed a diet deficient in nonessential AA (NEAA) N. In total, 48 barrows with a mean initial BW of 13.6 kg (SD 0.7) were used. At the beginning of the study, 8 pigs were euthanized for determination of initial protein mass. The remaining animals were individually housed and fed 1 of 5 dietary treatments. A common basal diet (95% of experimental diets) was formulated to meet the requirements for all essential AA (EAA) but to be deficient in NEAA N (CP = 8.01%). The basal diet was supplemented (5%) with cornstarch (negative control) or 2 N sources (ammonia or NEAA) at 2 levels each to supply 1.35 or 2.70% extra CP. The final standardized ileal digestible (SID) NEAA content in the high-NEAA-supplemented diet (positive control) was based on the NEAA profile of whole-body protein of 20-kg pigs, and it was expected to reduce the endogenous synthesis of NEAA. Pigs were fed at 3.0 times maintenance energy requirements for ME in 3 equal meals daily. At the end of a 3-wk period, pigs were euthanized and the carcass and visceral organs were weighed, frozen, and ground for determination of protein mass. From pigs in the initial, negative control, high-ammonia, and high-NEAA groups, AA contents in the carcass and pooled visceral organs were analyzed to determine the total and deposited protein AA profile, dietary EAA efficiencies, and minimal de novo synthesis of NEAA. Carcass weight and whole-body N retention linearly increased (P< 0.05) with N supplementation. The AA profile of protein and deposited protein in the carcass was not different (P> 0.10) between N sources, but Cys content increased (P< 0.05) with NEAA compared with ammonia in visceral organ protein and deposited protein. The dietary SID EAA efficiency for increasing EAA deposition in whole-body protein increased (P< 0.05) with N supplementation, but it was not different (P> 0.10) between N sources. The de novo synthesis of NEAA increased (P< 0.05) for ammonia compared with NEAA supplementation. In conclusion, adding ammonia as a N source to diets deficient in NEAA N increases whole-body N retention without affecting the carcass AA profile.

Inclusion of NPN in diets may compensate the deficient supply of nonessential AA (NEAA) in very low CP levels. To assess this, 2 studies were conducted to determine the effect of supplementing NPN and specific NEAA to diets severely deficient in NEAA nitrogen (NEAA-N) on growth performance of pigs. In Exp. 1, 48 gilts (initial BW 15.2 ± 1.3 kg; 2 pigs per pen; 6 pens per treatment) were randomly assigned to 1 of the 4 dietary treatments: 1) positive control (Pos Ctrl), not deficient in essential AA (EAA) and total N, with all N supplied from intact protein (casein and soybean meal) or crystalline EAA, (2) negative control (Neg Ctrl), supplying the same amount of potentially limiting EAA as Pos Ctrl but deficient in NEAA-N, 3) Neg Ctrl plus 1.45% CP from ammonia-N (low NPN), and 4) Neg Ctrl plus 2.90% CP from ammonia-N (high NPN), supplying the same amount of digestible N as the Pos Ctrl diet. Pigs were fed ad libitum, and ADG and ADFI were monitored weekly during a 3-wk period. Gain:feed improved linearly (P< 0.05) with supplementation of ammonia-N in diets. Gain:feed for high NPN was similar (P= 0.496) to that for Pos Crtl (0.51 and 0.52, respectively). In the Exp. 2, 72 individually housed barrows (initial BW 13.5 ± 0.6 kg; 8 pigs per treatment) were assigned to 9 dietary treatments. A basal diet was formulated to be deficient in NEAA-N with a ratio of EAA-N to total N (EAA-N:TN) of 0.74. The basal diet was supplemented with 1 of 4 different N sources (urea, ammonia, glutamic acid, and a mixture of NEAA) at 2 levels each, decreasing the final EAA-N:TN to 0.63 and 0.55, respectively. Pigs were fed at 3.0 times maintenance energy requirements during 9 d of adaptation and 3 wk of observations. Body weight was monitored weekly. At the end of the experiment, blood samples from the portal vein and abdominal aorta were collected to determine ammonia- and urea-N concentrations. Final BW, ADG, and G:F increased (P< 0.05) with supplemented ammonia, glutamate, and the NEAA mix but not (P> 0.10) with urea. Final BW, ADG, and G:F were not different (P> 0.05) between pigs fed the ammonia, glutamate, and NEAA mix supplemented diets. Urea concentration in portal and arterial blood plasma increased linearly (P< 0.05) with urea intake. In conclusion, growing pigs can utilize N from ammonia as efficiently as intact protein or NEAA as a source of extra N when diets are severely deficient in NEAA-N.

The concept of compensatory growth (CG) represents a means to improve nutrient utilization and decrease costs in pork production. While CG can occur following a period of amino acid intake restriction, there is limited work examining CG in newly weaned pigs. A serial slaughter study was conducted to determine effects of Lys restriction immediately following weaning on growth performance and carcass composition. 144 Duroc × Yorkshire × Landrace pigs (initial BW of 6.9 ± 0.21 kg) were randomly allocated to one of three dietary treatments (6 pens/treatment with 8 pigs/pen; 4 barrows, 4 gilts). For 3 wk (restriction phase), pigs were fed starter diets containing 110% (Control: 15.6 g/kg), 80% (Lys80: 11.3 g/kg), or 60% (Lys60: 8.5 g/kg) of NRC (2012) requirements for Lys. After the restriction phase, all pigs were fed a common grower diet containing 120% of NRC (2012) requirements for Lys (14.6 g/kg) for 6 wk (recovery phase). During the restriction phase, pig BW gain (P< 0.01; 411, 373, and 319 ± 7.5 g/d, respectively for Control, Lys80, Lys60) and G:F (P< 0.01; 0.807, 0.716, and 0.631 ± 0.0123, respectively) decreased linearly with decreasing dietary Lys levels. At end of the restriction phase, there was a significant linear decrease in BW with decreasing dietary Lys levels (P< 0.01; 15.5, 14.8, and 13.6 ± 0.37 kg, respectively). In addition, there was a linear decrease in carcass weight (P< 0.01; 11.6, 10.9, and 10.3 ± 0.30 kg, respectively) and carcass CP content (P< 0.01; 16.5, 16.1, and 15.3 ± 0.19%, respectively) with decreasing dietary Lys levels in pigs slaughtered at end of restriction phase. Following completion of the recovery phase there was a trend for a linear increase in BW gain (P= 0.06; 844, 862, and 905 ± 19.9 g/d, respectively) and a linear increase in G:F (P< 0.01; 0.529, 0.552, and 0.569 ± 0.0101, respectively) with decreasing dietary Lys levels. Carcass weight (P> 0.10; 40.5, 40.3, and 39.6 ± 0.80 kg, respectively) and carcass CP content (P> 0.10; 16.8, 17.4, and 17.1 ± 0.18%, respectively) were similar across dietary treatments in pigs slaughtered at end of recovery phase. At the end of the study, BW (average of 50.5 ± 0.63 kg) was similar (P> 0.10) across dietary treatments. In conclusion, newly weaned pigs previously fed a diet restricted in Lys for 3 wk, achieved full CG after a 6 wk recovery period.