Compensatory nitrogen retention in growing pigs following a period of N deprivation.

1. Semi-synthetic diets, with dried microbial cells (Pruteen) as the nitrogen source, were used to measure N retention in 50 kg pigs given different combinations of N intake involving periods of deprivation and enhanced supply. 2. Metabolic faecal N losses were 1.92 g/d (1.26 g/kg dry matter eaten) and endogenous urinary losses were 3.96 g/d for pigs given an N intake of 6.9 g/d. 3. Compensatory N retention averaging 4.2 g extra N/d was observed in pigs given enhanced N supply by diets providing 31.0, 60.4 and 93.4 g N/d. In some instances enhanced N retention was maintained for 22 d. 4. Pigs given enhanced N supply by extravagant N intake did not maintain the compensatory response which had been evident initially.

Efficiency of use of nitrogen from dried microbial cells after a period of N deprivation in growing pigs.

1. Semi-synthetic diets, with dried microbial cells (Pruteen) as the nitrogen source, were used to measure N retention in 50 kg pigs which had been given only sufficient N (5.3 g/d) to maintain N equilibrium for the previous 12 d. Control pigs were given 33.2 gN/d. 2. Metabolic faecal N losses were 1.62 g/d (1.2 g/kg dry matter eaten) and endogenous urinary losses were 3.90 g/d. 3. Realimentation of N-deprived pigs was achieved with diets providing 20.0, 33.2 and 67.4 g N/d and daily rates for N retention were 11.2, 17.8 and 25.9 respectively; the corresponding value for control pigs was 15.0 g. 'Catch-up' protein growth was demonstrated in pigs given both 33.2 and 67.4 g N/d. In the former instance, this was associated with an increase in the efficiency of utilization of dietary N. 4. The biological value of the protein in Pruteen was 0.85, and it appeared that under conditions of increased demand for N the pig could utilize some of the nucleic acid-N fraction of this protein source.