A simple amino acid dose-response method to quantify amino acid requirements of individual meal-fed pigs

Two experiments were conducted to develop a simplified dose-response technique to estimate the Lys requirement of individual, meal-fed growing pigs. In Exp. 1, we studied adaptation processes that occur during such a dose-response study in meal-fed pigs, and in Exp. 2, we studied the accuracy of this simplified technique to estimate changes in Lys requirement estimates of pigs following changes in energy intake. In Exp. 1, the effect of the Lys supply strategy on the Lys requirement was assessed in 14 barrows fed an increasing [low to high (LH)] or decreasing [high to low (HL)] total Lys supply, with total Lys levels varying from 0.36 to 1.06 g/MJ DE in 7 equidistant steps of 4 d each. Urinary urea and ammonia excretion and whole body N turnover were measured. In Exp. 2, the accuracy of the dose-response technique to determine a shift in Lys requirement was assessed in 20 barrows fed at either 2.2 [low energy (LE)] or 2.7 [high energy (HE)] times the energy requirements for maintenance, with total Lys supply decreasing from 1.10 to 0.37 g Lys/MJ DE in 9 equidistant steps of 3 d each. In Exp. 1, a lower increment in protein synthesis, breakdown, and whole body N turnover with increasing dietary Lys supply was observed in LH pigs than HL pigs (P < 0.01) and the estimated Lys requirement was 0.06 g/MJ DE greater (P = 0.01) in LH pigs than HL pigs. These results indicated that pigs at a decreasing Lys supply strategy require less time for metabolic adaptation to a change in Lys supply than those at an increasing Lys supply. In Exp. 2, the estimated Lys requirement was 2.6 g/d greater (P < 0.001) in HE pigs than LE pigs. The variation in AA requirement estimates between individual pigs was low (4.9% in LH pigs and 3.0% in HL pigs in Exp. 1 and 8.1% in LE pigs and 6.0% in HE pigs in Exp. 2). The present studies indicated that a dose-response technique with a decreasing Lys supply in time and a step length of 3 d with urinary N excretion as response criteria provides a simple, accurate technique to quantitatively estimate a change in AA requirements of individual meal-fed pigs.