Effects of Standardized Ileal Digestible Lysine on Growth Effects of Standardized Ileal Digestible Lysine on Growth Performance and Economic Return of 108 to 178 lb Grow-Finish Performance and Economic Return of 108 to 178 lb Grow-Finish Pigs Pigs

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Introduction
Lysine is typically the first limiting amino acid in corn-soybean meal-based swine diets. Other essential amino acids are formulated as a percentage of standardized ileal digestible (SID) Lys. Thus, it is critical to establish the SID Lys requirement in order to investigate next-limiting amino acid ratios. While genetic suppliers provide amino acid requirements for the various body weight ranges of their specific genetics, validating these levels is needed within production systems to achieve maximum lean growth and optimal feed cost. Along with standard statistical analysis procedures for growth performance, advanced dose-response models are helpful for estimating the pig's nutrient requirements and optimal economics more precisely. 5 Therefore, the objective of this study was to determine the optimum SID Lys requirement for growth performance and economic return of finishing pigs from 108 to 178 lb.

Materials and Methods
The Pipestone Institutional Animal Care and Use Committee approved the protocol used in this experiment. This study 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 selffeeder 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 2,124 barrows and gilts (PIC 1050 × DNA 600; initially 107.9 ± 1.31 lb) were used in a 32-d study to determine the optimal dietary SID Lys level for approximately 108 to 178 lb pigs in a commercial setting. Pens of pigs were blocked by location in the barn and randomly allotted to 1 of 5 dietary treatments with 24 to 27 pigs per pen and 16 replications per treatment. A similar number of barrows and gilts were placed in each pen. Diets were fed over 3 phases (108 to 129, 129 to 156, and 156 to 178 lb, respectively). Dietary treatments were corn-soybean meal-based and contained 10% (phase 1 and 2) or 5% (phase 3) DDGS. Diets were formulated to 85, 95, 103, 110, or 120% of the 2016 PIC 4 SID Lys recommendations for gilts as follows: phase 1 SID Lys levels of 0.90, 1.01, 1.09, 1.17 and 1.27%; phase 2 levels of 0.79, 0.87, 0.94, 1.03, and 1.10%; and phase 3 levels of 0.71, 0.78, 0.85, 0.92, and 0.99%, respectively (Tables 1 and 2). During the trial, pens of pigs were weighed, and feed disappearance was recorded on d 0, 10, 22, and 32 to determine ADG, ADFI, and F/G.
For the economic analysis, total feed cost per pig, feed cost per lb of gain, revenue, and income over feed cost (IOFC) were calculated. Diet costs were determined using the following ingredient costs: corn = $3.36/bu ($120/ton); soybean meal = $300/ ton; L-Lys HCl = $0.65/lb; DL-methionine = $1.04/lb; L-threonine = $0.77/lb; and L-tryptophan = $2.63/lb. Feed cost per pig was determined by total feed intake multiplied by diet cost ($/lb). Feed cost per lb of gain was calculated by dividing the total feed cost per pig by the total lb gained overall. Revenue per pig 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 minus feed cost per pig.
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 the 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
In phase 1 (d 0 to 10), increasing SID Lys increased (linear, P ≤ 0.001) ADG and F/G (Table 3). In phase 2 (d 10 to 22), there was a marginally significant improvement (linear, P ≤ 0.048) in F/G as SID Lys increased in the diet. In phase 3 (d 22 to 32), increasing SID Lys increased ADG and improved F/G (quadratic, P < 0.05). There was no effect on ADFI throughout all three phases (Table 3).
For overall growth performance (d 0 to 32), increasing SID Lys increased (linear, P < 0.001) final body weight, ADG, Lys intake/d, and Lys intake/kg of gain (Table 3). For F/G there was an improvement (quadratic, P = 0.047) as dietary SID Lys increased. There was no effect on pig removals, mortality, or total pigs removed from pens.
In summary, under these experimental conditions, growth performance increased linearly up to 120% of the 2016 PIC Lys recommendation, while the optimum IOFC was 105.8% to 113.7%.
Brand names appearing in this publication are for product identification purposes only. No endorsement is intended, nor is criticism implied of similar products not mentioned. Persons using such products assume responsibility for their use in accordance with current label directions of the manufacturer.   Corn was valued at $3.36/bu ($120/ton), soybean meal at $300/ton, L-Lys at $0.65/lb, DL-methionine at $1.04/lb, L-threonine at $0.77/lb, and L-tryptophan at $2.63/lb. 4 Feed cost/lb gain = (feed cost/pig) / total gain. 5 Total revenue/pig = (total gain/pig × 0.75) × $0.70. 6 Income over feed cost = total revenue/pig -feed cost/pig.  Figure 1. Estimation of standardized ileal digestible lysine requirement to maximize IOFC for 108 to 178 lb grow-finish pigs.

IOFC BLL
A total of 2,124 barrows and gilts (PIC 1050 × DNA 600; initially 107.9 ± 1.31 lb) were used in a 32-d growth trial with 24 to 27 pigs per pen and 16 replications per treatment. 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).