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This study aimed to investigate the effect of increasing the standardized ileal digestible (SID) total sulfur amino acid to lysine (TSAA:Lys) on the growth performance of nursery pigs raised with or without antibiotics (AGP) and to determine the optimal SID TSAA:Lys in nursery pigs raised without AGP. In Exp. 1, 924 nursery pigs (7.9 ± 1.3 kg), blocked by initial BW and sex, were randomly allotted to one of six treatments, with seven pens per treatment and twenty-two pigs per pen. The treatments were arranged in a 2 × 3 factorial design, with two AGP levels (0 or 50 mg/kg Carbodox) and three levels of SID TSAA:Lys (51.0, 58.5 or 66.0%). In Exp. 2, 990 weaned piglets (5.1 ± 0.9 kg), blocked by initial BW and sex, were randomly allotted to one of five dietary treatments (SID TSAA:Lys at 51, 58, 65, 72 or 79%) in the absence of AGP, with nine pens per treatment and twenty-two pigs per pen. Competing heteroskedastic models including broken-line linear (BLL), broken-line quadratic (BLQ), and quadratic polynomial (QP) were fitted for the growth performance data to estimate the optimal TSAA:Lys. In Exp. 1, AGP supplementation increased (p < 0.05) ADG and ADFI during the 21 d period. Increasing SID TSAA:Lys in the diets with AGP did not affect growth performance; however, increasing SID TSAA:Lys in the diets without AGP resulted in a linear increase (p < 0.05) in ADG and G:F. In Exp. 2, the best-fitting models for ADG and G:F from d 0 to 21 post-weaning were BLL, which yielded the optimal SID TSAA:Lys of 62% and 72%, respectively. The best-fitting models for ADG and G:F from d 21 to 42 post-weaning were BLL, which yielded the optimal SID TSAA:Lys of 59% and 58%, respectively. In conclusion, SID TSAA to Lys requirements under an antibiotic-free feeding regime during the first 21 d post-weaning were 62% and 72% in terms of ADG and G:F, respectively, whereas an SID TSAA:Lys of approximately 58% was required to maximize ADG and G:F for the late nursery phase.

Our objective was to determine the effects of feeding different neutral detergent fiber (NDF) and standardized ileal digestible (SID) lysine (Lys) levels on performance of growing-finishing pigs from 30- to 130-kg. A total of 2,016 barrows and gilts (PIC 280×Camborough, initial BW of 29.6±0.53 kg) were allotted to a randomized complete block design with a 2×2 factorial arrangement. Dietary treatments (Table 1) consisted with two NDF levels (13% or 20%) and two SID Lys curves (PIC2008 or PIC2016). There were 21 mixed-sex pigs per pen, and 24 pens per treatment. The experiment diets were fed in 3 phases. Wheat, wheat by-products, peas, and canola oil were used with NRC (2012) loading values to achieve treatments, and all diets were formulated to be iso-caloric (2,420 kcal NE/kg). Experimental data were analyzed using generalized linear mixed models with pen as the experimental unit. Increasing NDF level resulted in a reduction (P< 0.05) in average daily gain (ADG), average daily feed intake, hot carcass weight, carcass yield, carcass ADG, and backfat depth (Table 2), and tended to decrease percentage of removals and mortality (P=0.10). Pigs fed PIC2016 Lys curve had greater ADG and carcass ADG as compared to those fed PIC2008 Lys curve (P< 0.05). There were NDF×Lys interactions (P< 0.10) for ADG, gain to feed ratio (G:F), carcass ADG, and carcass G:F. These response criteria were improved for pigs fed PIC2016 Lys curve compared to those fed PIC2008 Lys curve when NDF level was 13%; while no evidence of differences was observed at 20% NDF. Results indicate that increasing NDF level from 13 to 20% deteriorate performance of 30- to 130-kg pigs; and the improved growth performance of pigs fed PIC2016 Lys curve as compared to those fed PIC2008 Lys curve was only observed when lower NDF level was presented. [ABSTRACT FROM AUTHOR]