Effect of severe amino acid restriction on subsequent growth performance and urinary N excretion in growing pigs

Using 12 gilts (initial body weight: 38.4±1.1 kg), we investigated an effect of early dietary amino acid (AA) restrictions on daily changes in urinary N excretion and growth performance during the following re-alimentation period. After the 10-d preliminary period of using a high-protein diet, we estimated protein deposition rate (PD) of pigs, two 14-d experimental periods followed. Pigs were allotted to 2 groups so as the mean PD of both groups was similar. During the first 14-d restriction period, the control group was fed an AA adequate diet, while the restricted group was fed an AA deficient diet. During the following 14-d re-alimentation period, both groups were fed AA adequate diet. Starting on d 12 of the restricted period, samples of urine were collected from both groups using permanent bladder catheters to monitor daily N excretion. Pigs were weighed weekly, the remaining feed were collected daily, and average daily feed intake (ADFI), average daily gain (ADG), gain:feed (G:F) were calculated for each period separately and overall for the restriction and re-alimentation periods. For the same periods, urinary N excretion rate was determined. During the re-alimentation period, pigs that were previously fed the AA deficient diet tended (P=0.060) to have greater ADFI (2297 vs. 2171 g/d), and greater (P<0.05) ADG (1216 vs. 827 g/d) and G:F (529 vs. 379 g/kg) than the control group. There were no differences in urinary N excretion between the restricted (20.8 g/d) and control (21.2 g/d) groups. During the overall period, lower (P<0.05) ADG (643 vs. 817 g/d) and G:F (294 vs. 381 g/kg) were observed in the restricted group compared with the control group. There was lower urinary N excretion in the restricted group in comparison to the control group as a result of early dietary AA restrictions. After early dietary AA restrictions, pigs demonstrated compensatory response in growth performance, but reduction in urinary N excretion was observed for only a short-term. During the overall period, including the restriction and re-alimentation period, compensatory growth was not observed, and lower urinary N excretion was resulted from early dietary AA restrictions. Compensatory response was not strong enough to offset the differences caused by severe early dietary AA restrictions.