Effects of Standardized Ileal Digestible Lysine on Growth Performance and Economic Return of 200 to 300 lb Grow-Finish Pigs

A total of 2,099 barrows and gilts (PIC 1050 × DNA 600; initially 198.6 ± 3.72 lb) were used in a 57-d study to determine the optimal dietary standardized ileal digestible (SID) Lys level for approximately 200 to 300 lb pigs in a commercial setting. Pigs were randomly allotted to 1 of 4 dietary treatments with 24 to 27 pigs per pen and 20 replications per treatment. A similar number of barrows and gilts were placed in each pen. Diets were fed over 2 phases (199 to 233 and 233 to 299 lb respectively). Dietary treatments were corn-soybean meal-based. Diets were formulated to 85, 93, 100, or 110% of the 2016 PIC (Hendersonville, TN) SID Lys gilt recommendations with phase 1 SID Lys levels of 0.65, 0.71, 0.77, 0.84%, and phase 2 levels of 0.60, 0.66, 0.71, 0.78%, respectively. Overall (d 0 to 57), increasing SID Lys increased (linear, P < 0.05) overall market weight, F/G, hot carcass weight, Lys intake/d, and Lys intake/kg of gain with an increase in ADG (quadratic, P = 0.020). For economics (d 0 to 57), feed cost per lb of gain increased (linear, P < 0.05) with increased SID Lys. Revenue per pig placed and income over feed cost (IOFC) increased (quadratic, P < 0.10) as the amount of SID Lys increased, and marginally significant evidence of a quadratic response for feed cost per pig placed (P = 0.073). Projecting IOFC for phase 1, the quadratic polynomial (QP) and broken-line linear models estimated the requirement at 110.9% and 96.9%, respectively, to achieve maximum IOFC. For phase 2, the QP estimated the requirement at 96.6% SID Lys to maximize IOFC. In summary, the SID Lys requirement was 97% to 111% of the 2016 PIC recommended Lys requirement for phase 1 and 97% for phase 2 to maximize IOFC.


Summary
A total of 2,099 barrows and gilts (PIC 1050 × DNA 600; initially 198.6 ± 3.72 lb) were used in a 57-d study to determine the optimal dietary standardized ileal digestible (SID) Lys level for approximately 200 to 300 lb pigs in a commercial setting. Pigs were randomly allotted to 1 of 4 dietary treatments with 24 to 27 pigs per pen and 20 replications per treatment. A similar number of barrows and gilts were placed in each pen. Diets were fed over 2 phases (199 to 233 and 233 to 299 lb respectively). Dietary treatments were corn-soybean meal-based. Diets were formulated to 85, 93, 100, or 110% of the 2016 PIC 4 (Hendersonville, TN) SID Lys gilt recommendations with phase 1 SID Lys levels of 0.65, 0.71, 0.77, 0.84%, and phase 2 levels of 0.60, 0.66, 0.71, 0.78%, respectively. Overall (d 0 to 57), increasing SID Lys increased (linear, P < 0.05) overall market weight, F/G, hot carcass weight, Lys intake/d, and Lys intake/kg of gain with an increase in ADG (quadratic, P = 0.020). For economics (d 0 to 57), feed cost per lb of gain increased (linear, P < 0.05) with increased SID Lys. Revenue per pig placed and income over feed cost (IOFC) increased (quadratic, P < 0.10) as the amount of SID Lys increased, and marginally significant evidence of a quadratic response for feed cost per pig placed (P = 0.073). Projecting IOFC for phase 1, the quadratic polynomial (QP) and broken-line linear models estimated the requirement at 110.9% and 96.9%, respectively, to achieve maximum IOFC. For phase 2, the QP estimated the requirement at 96.6% SID Lys to maximize IOFC. In summary, the SID Lys requirement was 97% to 111% of the 2016 PIC recommended Lys requirement for phase 1 and 97% for phase 2 to maximize IOFC.

Introduction
Providing optimum dietary Lys is crucial for maximizing lean growth and reducing feed cost in grow-finish pigs. There are several factors that impact optimal dietary concentration of dietary Lys including genetics, environment, sex, and weight of the pig. 5 The genetics of modern pigs continue to advance and have potentially altered nutrient requirements. As a result, dietary nutrient requirements need to be re-evaluated over time. 6 Therefore, the objective of this study was to determine the optimum standardized ileal digestible (SID) Lys requirement for growth performance and economic return of finishing pigs from 200 to 300 lb.

Materials and Methods
The Pipestone Institutional Animal Care and Use Committee approved the protocol used in this study. This experiment was conducted at a commercial wean-to-finish research facility located in southwest Minnesota (Pipestone Applied Research; Edgerton, MN). Each pen contained one nipple waterer and a 1-hole wet/dry feeder or a 4-hole dry self-feeder for ad libitum access to feed and water. Treatments were equally allotted and replicated across different feeder types. Diets were manufactured at the Spronk Brothers feed mill in Edgerton, MN. A robotic feeding system (FeedPro; Feedlogic Corp., Wilmar, MN) was used to deliver and record daily feed additions to each individual pen.
A total of 2,099 barrows and gilts (PIC 1050 × DNA 600; initially 198.6 ± 3.72 lb) were used in a 57-d study to determine the optimal dietary SID Lys level of approximately 200 to 300 lb pigs in a commercial setting. Pens of pigs were blocked by location in the barn and randomly allotted to 1 of 4 dietary treatments with 24 to 27 pigs per pen and 20 replications per treatment. A similar number of barrows and gilts were placed in each pen. Diets were fed over 2 phases (199 to 233 and 233 to 299 lb, respectively). Dietary treatments were corn-soybean meal-based. Diets were formulated to 85, 93, 100, or 110% of the 2016 PIC (Hendersonville, TN) SID Lys recommendations for gilts, with phase 1 SID Lys levels of 0.65, 0.71, 0.77, 0.84%, and phase 2 levels of 0.60, 0.66, 0.71, 0.78%, respectively (Table 1). During the trial, pens of pigs were weighed, and feed disappearance was recorded on d 0, 16, 29, 44, and 57 to determine ADG, ADFI, and F/G (Table 2). Pigs were individually ear tagged with RFID ear tags prior to the start of this trial. On d 29 and 44, eight of the heaviest pigs per pen were weighed individually and transported to a commercial packing plant (WholeStone Farms, Fremont, NE) for processing and determination of carcass characteristics. The remaining pigs were marketed at the conclusion of this trial on d 57 and also transported to WholeStone Farms for carcass characteristic collection.
For the economic analysis, total feed cost per pig, cost per lb of gain, revenue, and income over feed cost (IOFC) were calculated. Feed cost per pig placed was determined by multiplying total feed intake by diet cost. Feed cost per lb of gain was calculated by dividing the total feed cost per pig by the total weight gained. Revenue per pig placed Kansas State University Agricultural Experiment Station and Cooperative Extension Service was determined by total gain times the dressing percentage (0.75) and then multiplied by $0.70 carcass price in order to convert to a live price. Income over feed cost was calculated using revenue per pig placed minus feed cost per pig placed. For all economic evaluations, the following ingredients costs were used: corn = $3.94/bu ($140.80/ton); soybean meal = $320/ton; L-Lys HCl = $0.65/lb; DL-methionine = $1.12/lb; L-threonine = $0.63/lb; and L-tryptophan = $3.23/lb.
Data were analyzed using the GLIMMIX procedure of SAS OnDemand for Academics (SAS Institute, Inc., Cary, NC) in a randomized complete block design with pen as the experimental unit and location as the blocking factor. Treatments were considered a fixed effect and block as a random effect. Contrast coefficients were adjusted to account for unequal spacing of Lys treatments. Dose response curves were evaluated using linear (LM), quadratic polynomial (QP), broken-line linear (BLL), and broken-line quadratic (BLQ) models. For each response variable, the best-fitting model was selected using the Bayesian information criterion (BIC). Results were considered significant with P ≤ 0.05 and were considered marginally significant with P ≤ 0.10.

Results and Discussion
For phase 1 growth performance (d 0 to 16), increasing SID Lys improved (linear, P < 0.001) ADG and F/G (Table 2). We observed a marginally significant increase (quadratic, P = 0.057) in ADFI as SID Lys increased. For phase 2 (d 16 to 57), we observed increased (quadratic, P = 0.045) ADG as SID Lys was increased, but no effect on ADFI or F/G.
For overall growth performance (d 0 to 57), increasing SID Lys increased (linear, P < 0.05) the overall market weight, HCW, F/G, Lys intake/d, and Lys intake/kg of gain. Average daily gain increased (quadratic, P = 0.020) with the greatest response observed in pigs fed 100% of the 2016 PIC feeding level, with no improvement observed thereafter. For ADFI, a marginally significant increase (quadratic, P = 0.092) was observed as SID Lys was increased.
For economic analysis in phase 1 (d 0 to 16), we observed increased (linear, P < 0.05) revenue per pig placed, and IOFC as SID Lys increased (Table 3). For feed cost per pig placed we observed a marginal increase (quadratic, P = 0.057) as SID Lys increased. For phase 2, increasing SID Lys increased (linear, P < 0.05) the feed cost per pig placed. A quadratic response was observed for revenue per pig placed (P = 0.048) as SID Lys increased, where pigs fed 100% of the SID Lys requirement had the greatest revenue per pig placed with no improvement observed thereafter. A marginally significant increase (quadratic, P = 0.061) was observed for IOFC with the greatest response observed at 100% of the PIC 2016 SID Lys estimate. For overall economics (d 0 to 57), feed cost per lb of gain increased (linear, P < 0.05) with increasing SID Lys. Revenue per pig placed and IOFC increased (quadratic, P < 0.05) as SID Lys increased. Feed cost per pig placed tended to increase as the amount of SID Lys increased (quadratic, P = 0.073).
For modeling IOFC, data were analyzed separately for each phase. In phase 1, the QP and BLL models had a comparable fit (BIC = 279.6 and 279.8, QP and BLL, respectively) with the SID Lys requirement to achieve maximal performance being predicted at 110.9% with QP, and 96.9% for the BLL model (Figure 1). In summary, the SID Lys requirement was determined to be 97% to 111% of the 2016 PIC feeding recommendations depending on the model used for phase 1, and 97% for phase 2 to maximize IOFC.

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