Growing pigs’ simulated amino acid requirements differs between actual factorial methods

Abstract Text: The objective of this study was to compare actual factorial methods used to estimate phase-feeding growing pigs' lysine requirements with the method developed for precision feeding (PF) which provides individual pigs with daily tailored diets. Data from 36 high-performance pigs (25 kg initial BW, MSE= 2.23) were used in a 28-d trial. Observed individual daily net energy (NE) intake and BW gain were smoothed by linear regression and used to estimate individual and population standardized ileal digestible lysine (SIDLys) requirements. BW gain was assumed constant (regression slope) for every pig within the trial. The PF individual SIDLys requirements were calculated daily assuming 16% protein in daily gain, 7% lysine in protein and 72% SIDLys retention efficiency plus the maintenance (Hauschild et al., 2012). Phase-feeding SIDLys population requirements were estimated with the Brazilian (BT, Rostagno et al., 2011), NRC (2012) and PF factorial methods. These requirements were estimated as recommended using the average pig in the middle of the phase in BT and NRC methods and the 80 centile pig of the population at the beginning of the phase in the PF method. Between-animal variation in SIDLys requirements varied from 22% at the beginning to 8% at the end of the trial. Daily population BT and NRC SIDLys requirements were respectively 15 and 13% higher than the average daily PF model requirements. When using these models to estimate the optimal population SIDLys concentration to be served in the studied 28-days feeding phase, BT and NRC methods (i.e., average pig in the middle of the phase) yielded similar recommendations (3.48 and 3.44 SIDLys g/Kcal NE, respectively), but were, in average, 22% lower than the estimated by the PF method (i.e., 80 centile pig at the beginning of the phase). In the first day, 64, 69 and 25% of pigs were underfed with the BT, NRC, and PF methods, respectively, for a total period, in the same order, of 16, 18, and 2% of the 1008 pig-day estimations. The BT and NRC methods were calibrated for maximum population responses this explaining why they overestimate the daily average animal requirements by more than 13%, and yield a value close to the 80 centile pig of the population. The average pig in the middle of the feeding phase has to be used with caution to estimate requirements of this phase given the large variation in nutrient requirements that exist between and across pigs over time. Keywords: lysine, NRC, precision nutrition, swine