Effects of Feeding Increasing Standardized Ileal Digestible Lysine Effects of Feeding Increasing Standardized Ileal Digestible Lysine on Growth Performance of 26-to 300-lb PIC Line 800-Sired Pigs on Growth Performance of 26-to 300-lb PIC Line 800-Sired Pigs

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Summary
The objective of this study was to evaluate the growth performance and economic returns of PIC 800 × 1050 pigs fed increasing SID Lys from approximately 26 to 300 lb.Pens of pigs were blocked by BW and randomly assigned to 1 of 5 dietary treatments in a randomized complete block design with 26 pigs per pen and 16 pens per treatment.Pens were provided 1 of 5 dietary treatments with increasing SID Lys at 85, 93, 100, 107, and 115% of current PIC recommendations within 6 different phases.Two base diets containing low Lys and high Lys were blended to meet target SID Lys levels for each treatment diet within phase.For the overall experimental period (d 0 to 143), feeding increasing SID Lys improved (linear, P ≤ 0.007) ADG and F/G, but did not impact ADFI (P > 0.10).For carcass characteristics, a tendency (linear, P = 0.067) for increased HCW of pigs that were provided increasing SID Lys was observed.However, there was no evidence for differences (P > 0.10) across treatments in carcass yield, backfat depth, loin depth, or carcass lean percentage.Increasing SID Lys of the diets increased (linear, P < 0.001) feed cost and feed cost per lb of gain.There was no evidence of difference (P > 0.10) in revenue for either ingredient price scenario, thus, feeding increasing levels of SID Lys reduced (linear, P < 0.001) income over feed cost (IOFC) in both scenarios.The linear model (LM) served as the best fit for both growth and economic parameters.The LM model predicted maximum ADG and minimal F/G at levels greater than 115% of PIC's current SID Lys recommendations.For IOFC, the LM model predicted maximum profitability at or below 85% of PIC's current Lys recommendations.In conclusion, the optimal SID Lys level for PIC 800 × 1050 pigs from 26-to 300-lb depends upon the response criteria, with growth performance maximized at levels at or above 115% of PIC's recommendation for SID Lys; however,

Introduction
Lysine is considered the first limiting amino acid in diets for swine.It is important to supply pigs with sufficient lysine to support muscle growth and development while minimizing excess that will be excreted into the environment.Lysine requirements can be influenced by many factors including growth potential, genetics, gender, and health status.With rapid advancements in swine genetics, it is crucial to frequently evaluate Lys requirements.By optimizing SID Lys recommendations, the industry can maximize both lean muscle deposition and economic returns as growth performance and meat quality attributes improve.
Recently, PIC updated their SID Lys recommendations in the 2021 PIC Nutrition and Feeding Guidelines manual;4 however, these recommendations were based on PIC 337 × 1050 pigs. 5Currently, there is limited research available outlining the SID Lys recommendations for the PIC 800 sire line.Therefore, the objective of this study was to evaluate the growth performance and economic returns of PIC 800 × 1050 pigs fed SID Lys at 85, 93, 100, 107, and 115% of PIC Lys recommendations from approximately 26-to 300-lb.

Procedures
The protocol for this experiment was approved by the Kansas State University Institutional Animal Care and Use Committee.A commercial research barn located in south-central Minnesota was used to conduct the study.The barn had slatted concrete flooring, deep pits for manure storage, and was naturally ventilated.Pens contained a 3-hole stainless steel dry self-feeder (Thorp Equipment, Thorp, WI) to provide ad libitum access to feed.

Animals and diets
A total of 2,080 pigs (PIC 800 × 1050, Hendersonville, TN; initially 26.1 lb) were used in the experiment.Pens of pigs were blocked by BW and randomly assigned to 1 of 5 dietary treatments in a randomized complete block design.There were 26 pigs per pen with equal numbers of barrows and gilts and 16 replicates per treatment.Treatments consisted of 5 increasing SID Lys levels fed throughout 6 different phases as follows: phase 1 (1.09, 1.19, 1.28, 1.36, and 1.47%); phase 2 (0.97, 1.06, 1.14, 1.22, and 1.32%); phase 3 (0.87, 0.95, 1.02, 1.09, and 1.17%); phase 4 (0.75, 0.82, 0.88, 0.94, and 1.01%); phase 5 (0.66, 0.72, 0.77, 0.82, and 0.89%); and phase 6 (0.59, 0.64, 0.69, 0.74, and 0.79%).The approximate weight of pigs for each phase was 25 to 50, 50 to 90, 90 to 130, 130 to 180, 180 to 230, and 230 to 300 lb, respectively.The increasing SID Lys treatments represent 85, 93, 100, 107, and 115% of PIC recommendations within each phase of growth.Two base diets containing low Lys and high Lys were blended to meet the target SID Lys level for each treatment diet (Table 1).Lysine was the first limiting AA while all other AA ratios were maintained above requirement estimates.Experimental diets were fed from d 0 to 18, 18 to 41, 41 to 60, 60 to 82, 82 to 105, and 105 to 143 for phase 1 to 6, respectively.To determine ADG, ADFI, and F/G, pens of pigs were weighed, and feed disappearance was recorded throughout the trial.On d 116 and 123, the 4 heaviest pigs from each pen were marketed.The remaining pigs were marketed approximately 17 days later at the conclusion of the study.
At the conclusion of the study, individual pigs were weighed and tattooed with a pen identification number prior to transportation to a commercial abattoir for carcass data collection.Measurements including HCW, loin depth, backfat depth, and percentage lean were collected.The calculation for carcass yield was individual pig HCW at the plant divided by individual final pig weight on the farm.Individual carcass data were used in the analysis with pen serving as the experimental unit.Hot carcass weight served as a covariate for loin depth, backfat depth, and percentage lean in the statistical analysis.

Statistical analysis
Data were analyzed as a randomized complete block design for a one-way ANOVA using the GLIMMIX procedure of SAS v. 9.4 (SAS Institute, Inc., Cary, NC).Pen was considered the experimental unit, initial body weight served as a blocking factor, and treatment served as the fixed effect.Results were considered significant with P ≤ 0.05 and marginally significant with P ≤ 0.10.Dose response curves were evaluated using linear (LM), quadratic polynomial (QP), and broken-line linear (BLL) models.The best-fitting model was selected using the Bayesian Information Criterion (BIC) with improved model fits accepted when BIC decreased at least 2.0.

Results and Discussion
Increasing SID Lys increased (quadratic, P = 0.043) BW on d 41 and continued to increase (linear, P < 0.05) BW during all subsequent periods.From d 0 to 41, increasing SID Lys improved (linear, P < 0.001) F/G and increased (linear, P < 0.001) ADG; however, there was no evidence for differences (P > 0.10) in ADFI.From d 41 to 82, increasing SID Lys decreased ADFI and improved F/G (quadratic, P ≤ 0.01) when dietary Lys was provided at 93 or 100% of the 2021 PIC recommendation.Furthermore, from d 82 to marketing (d 143), there were no differences (P > 0.10) in ADG or ADFI, but F/G tended to improve (linear, P = 0.078) as SID Lys increased.For the overall experimental period (d 0 to 143), feeding increasing SID Lys improved (linear, P ≤ 0.007) ADG and F/G, but did not impact ADFI (P > 0.10).As expected, overall Lys intake/d and Lys intake/kg of gain increased (linear, P < 0.001) as SID Lys increased.
For carcass characteristics, there was a tendency (linear, P = 0.067) for an increase in HCW as SID Lys increased.However, there was no evidence for differences (P > 0.10) in any of the other carcass characteristics.
For economics, increasing levels of SID Lys increased (linear, P < 0.001) feed cost and feed cost per lb of gain in both the low-and high-priced ingredient scenarios.However, there was no evidence of differences (P > 0.10) for revenue in either of the price scenarios due to increasing SID Lys.Thus, IOFC decreased (linear, P < 0.001) as SID Lys increased, regardless of the ingredient price scenario.
The LM model served as the best fit for both growth and economic criteria.The LM model predicted maximum ADG and minimal F/G at levels at or greater than 115% of PIC's current recommendations.For IOFC, the LM model predicted maximum profitability at or below 85% of PIC's current Lys recommendations.
In the current study, the optimal SID Lys level for PIC 800 × 1050 pigs from 26 to 300 lb depends upon the response criteria, with growth performance maximized at levels above 115% of PIC's current SID Lys recommendation; however, economic responses were maximized at or below 85% of PIC's current SID Lys recommendations.Therefore, despite an increase in growth performance, feeding greater than 85% of PIC Lys recommendation is not economically justified.

Table 1 .
Diet composition (as-fed basis)1,2 Kansas State University Agricultural Experiment Station and Cooperative Extension Service Kansas State University Agricultural Experiment Station and Cooperative Extension Service

Table 2 .
Effects of increasing SID Lys on growth performance of PIC 800-sired pigs 1

Table 2 .
Effects of increasing SID Lys on growth performance of PIC 800-sired pigs 1 2