310 Effects of Standardized Ileal Digestible (SID) Threonine: Lysine Ratio on Nursery Pig Performance.

Abstract

2.21, or 2.45 g/Mcal ME) with 12 replicate pens/trt and 14 to 18 pigs/pen (0.85 to 1.10 m 2 /pig). The low and high Lys:ME levels were formulated as corn-SBM diets utilizing crystalline Lys, Thr, Met, and Trp to obtain the targeted Lys:ME and maintaining all other SID AA:Lys at 10% above NRC (2012) requirements. Diets were formulated to be iso-caloric (3,307 kcal ME/kg) and contained a minimum of 12% CP. Intermediate Lys:ME diets were made by blending the low and the high at appropriate levels to obtain the targeted Lys:ME levels. Dietary treatments were fed for 21 d. Statistical analysis to identify effects of dietary treatment were performed using the MIXED procedure of SAS. For break-point analysis, the NLMIXED procedure of SAS was utilized for linear broken-line regression in order to account for initial BW blocking; best fit statistics are presented based on R 2 values. Average daily gain did not differ among the Lys:ME levels (0.88 to 0.93 ± 0.02 kg/d, P = 0.475). Average daily feed intake was linearly reduced with increasing Lys:ME; linear broken-line analysis was beyond the scope of the trial parameters (P = 0.034). Feed efficiency (G:F) tended to increase as SID Lys:ME increased from 1.49 to 2.45 g SID Lys/Mcal ME (0.27 vs. 0.29 ± 0.01, respectively , P = 0.07); linear broken-line analysis indicated efficiency was maximized at 2.21 ± 0.01 g SID Lys/Mcal ME (P = 0.01; R 2 = 0.80). Data from this trial indicate that feed efficiency is optimized at 2.21 g SID Lys/Mcal ME in pigs weighing between 129 and 149 kg BW. The ideal profile for standard ileal digestible (SID) iso-leucine is not known with confidence. The NRC (2012) estimated, through factorial calculation, the SID iso-leucine (ILE) profile to be 53% that of lysine (LYS) for 70 kg pigs. An empirical estimate was determined to be 60-62% at asymptote for 90 kg pigs, depending on criterion (D. Kendall, Ph D Dissertation, 2004). Our study was conducted to calibrate the NRC estimate for SID ILE profile in 70-100 kg pigs, so that amino acid (AA) displacement of SBM is not compromised by a deficit ILE level. A total of 1928 PIC terminal (TR-4 x Camborough) castrate and female pigs (70.9 ± 0.7 kg) were used in a 35 d growth assay to 102.4 kg (±0.9 kg). Pigs were placed in a commercial research facility, blocked by sex and weight then allocated (19 pigs/pen, with 0.78 m 2 /pig) to treatment. Treatments were arranged as a 2 x 5 factorial, involving sex and 5 ILE:LYS (SID) ratio's (0.50, 0.56, 0.62, 0.68, 0.74). Pen was the experimental unit (10 pens/diet x sex subclass). Diets were composed of corn, soybean meal, choice white grease (1.5%) and AA. Two diets were milled and summit blended to create three additional diets using the Howeema system. Diets were isocaloric with SID LYS:Mcal NE set to approx. 96% asymptote, based on internal whole-body gain and G:F response curves: 2.684 and 2.301 g SID LYS:Mcal NE from 70 to 90 kg and 90-102 kg respectively. Ratio to LYS for key AA met or exceeded NRC minimums: Thr, 0.68, Trp, 0.22, Met, 0.32, Met:Cys, 0.58, Val, 0.68. The SID LYS:CP ratio ranged from 0.0588 to 0.0603. Average daily feed intake was not affected by diet (P=0.86) and sex x diet was not significant (P>0.50). The G:F response to ILE:LYS ratio was quadratic (0.329, 0.336, 0.338, 0.339, 0.323, SEM ±0.005, P<0.01) and described as: Y=-0.0135 + 0.0117x-0.00010x 2 (R 2 =0.34, P<0.01). Average daily gain also responded in quadratic manner (0.904, 0.916, 0.924, 0.910, 0.887 kg/d, SEM ± 0.013, P=0.07); being represented as: Y= 9.1546 + 0.7682x-0.00638x 2 (R 2 =0.16, P=0.06). Growth-derived estimates for ILE:LYS (SID), at asymptote, were 0.61 and 0.60 for G:F and total gain, respectively. This exceeds the NRC estimate for the 70-100 kg pig and illustrates the importance of empirical calibration of ideal AA patterns.