Effects of Standardized Ileal Digestible Valine : Lysine Ratio on the Growth Performance and Economics of Finishing Pigs from 55 to 100

The objective of these experiments was to determine the effects of SID Val:Lys ratio in low CP and low lysine diets on the growth performance and economics of finishing pigs from 55 to 100 lb. In Exp. 1, a total of 1,134 gilts (PIC 337 × 1050, initially 68.8 lb BW) were used in a 19-d growth trial with 27 pigs per pen and seven pens per treatment in a randomized complete block design with pens blocked by initial average BW. There was a total of six dietary treatments: 59.0, 62.5, 65.9, 69.6, 73.0, and 75.5% SID Val:Lys ratio. In Exp. 2, a total of 2,100 gilts (PIC 327 × 1050, initially 56.6 lb BW) were used in a 22-d growth trial with 25 pigs per pen and 12 pens per treatment in a randomized complete block design with pens blocked by initial average BW. There was a total of seven dietary treatments: 57.0, 60.6, 63.9, 67.5, 71.1, 74.4, and 78.0% SID Val:Lys ratio. In both experiments, the intermediate Val:Lys levels were obtained by blending different proportions of the low and high Val:Lys diets. Responses measured at the pen level were analyzed using general linear and non-linear mixed models. Competing statistical models were: a broken-line linear ascending (BLL) model, a broken-line quadratic ascending (BLQ) model, and a quadratic polynomial (QP). Competing models were compared using Bayesian information criteria (BIC). In Exp. 1, ADG increased linearly (P = 0.009) with increasing SID Val:Lys ratio whereas ADFI only marginally increased (linear, P = 0.098) with no evidence for differences on F/G. Feed cost per pig, feed cost per lb of gain, and total revenue per pig increased (linear, P < 0.009) with increasing SID Val:Lys ratio without evidence for differences in IOFC. In Exp. 2, ADG and ADFI increased (P < 0.002) with increasing SID Val:Lys ratio resulting in an improvement in F/G (P < 0.001). Similarly, increasing SID Val:Lys ratio increased feed cost per pig (quadratic, P < 0.001), feed cost per lb of gain (linear, P < 0.001), total revenue (quadratic, P < 0.001), and IOFC (quadratic, P < 0.001). In conclusion, the SID Val:Lys ratio to optimize performance ranged from 71.0% for minimum F/G to 74.4% for maximum ADG. However, feed cost per lb of gain was minimized at less than 57% SID Val:Lys ratio and maximum income over feed cost was estimated at 62.3% SID Val:Lys ratio with a plateau thereafter. Therefore, 99% of the optimum ADG and F/G were estimated at approximately 69% and 65% SID Val:Lys ratio, respectively.


Summary
The objective of these experiments was to determine the effects of SID Val:Lys ratio in low CP and low lysine diets on the growth performance and economics of finishing pigs from 55 to 100 lb.In Exp. 1, a total of 1,134 gilts (PIC 337 × 1050, initially 68.8 lb BW) were used in a 19-d growth trial with 27 pigs per pen and seven pens per treatment in a randomized complete block design with pens blocked by initial average BW.There was a total of six dietary treatments: 59.0, 62.5, 65.9, 69.6, 73.0, and 75.5% SID Val:Lys ratio.In Exp. 2, a total of 2,100 gilts (PIC 327 × 1050, initially 56.6 lb BW) were used in a 22-d growth trial with 25 pigs per pen and 12 pens per treatment in a randomized complete block design with pens blocked by initial average BW.There was a total of seven dietary treatments: 57.0, 60.6, 63.9, 67.5, 71.1, 74.4, and 78.0%SID Val:Lys ratio.In both experiments, the intermediate Val:Lys levels were obtained by blending different proportions of the low and high Val:Lys diets.Responses measured at the pen level were analyzed using general linear and non-linear mixed models.Competing statistical models were: a broken-line linear ascending (BLL) model, a broken-line quadratic ascending (BLQ) model, and a quadratic polynomial (QP).Competing models were compared using Bayesian information criteria (BIC).In Exp. 1, ADG increased linearly (P = 0.009) with increasing SID Val:Lys ratio whereas ADFI only marginally increased (linear, P = 0.098) with no evidence for differences on F/G.Feed cost per pig, feed cost per lb of gain, and total revenue per pig increased (linear, P < 0.009) with increasing SID Val:Lys ratio without evidence for differences in IOFC.In Exp. 2, ADG and ADFI increased (P < 0.002) with increasing SID Val:Lys ratio resulting in an improvement in F/G (P < 0.001).Similarly, increasing SID Val:Lys ratio increased feed cost per pig

Introduction
Valine is commonly considered to be the fifth limiting amino acid after tryptophan in corn-soybean meal-based diets for finishing pigs (Figueroa et al., 2003) 5 .Valine can become limiting in diets supplemented with feed-grade amino acids such as lysine, methionine, tryptophan, and threonine.There are many ways to express swine amino acid requirements, but the most common approach for diet formulation is the expression of the standardized ileal digestible (SID) Val requirement as a ratio to Lys (Val:Lys).The NRC (2012) estimated SID Val:Lys ratio requirement at 65.3% for early finishing pigs.However, even though NRC provides a single estimate for the AA requirements, the estimates to optimize ADG, F/G or especially economic criteria such as feed cost per lb of gain or income over feed cost (IOFC) can vary significantly.Therefore, the objective of these experiments was to determine the effects of SID Val:Lys ratio in low CP and lysine-limiting diets on the growth performance and economics of finishing pigs from 55 to 100 lb.

Procedures
The Kansas State University Institutional Animal Care and Use Committee (IACUC) approved the protocol used in this experiment.Two experiments were conducted at commercial research facilities located in Minnesota.Both barns were naturally ventilated and double-curtain-sided and pens also had completely slatted flooring and deep pits for manure storage.In Exp. 1, pens were equipped with a 4-hole stainless steel dry self-feeder (Thorp Equipment, Thorp, WI) and a cup waterer.In Exp. 2, each pen was equipped with a 3-hole stainless steel dry self-feeder (Thorp Equipment, Thorp, WI) and a cup waterer.Both facilities were equipped with a computerized feeding system (FeedPro; Feedlogic Corp., Willmar, MN) that delivered and recorded daily feed additions.During the experiments, pigs had ad libitum access to feed and water.
In Exp. 1, a total of 1,134 gilts (PIC 337 × 1050, initially 68.8 lb BW) were used in a 19-d growth trial with 27 pigs per pen and 7 pens per treatment.In Exp. 2, a total of 2,100 gilts (PIC 327 × 1050, initially 56.6 lb BW) were used in a 22-d growth trial with 25 pigs per pen and 12 pens per treatment.In both experiments, treatments were blocked by initial BW in a randomized complete block design.For Exp. 1 there was a total of six dietary treatments: 59.0, 62.5, 65.9, 69.6, 73.0, and 75.5% SID Val:Lys ratio.For Exp. 2 there was a total of seven dietary treatments: 57.0, 60.6, 63.9, 67.5,  1 and 2).Diet samples were taken from 6 feeders per dietary treatment 3 d after the beginning and 3 d before the end of each experiment, then CP and total amino acid analysis was conducted on composite samples from each treatment (Ajinomoto Heartland, Inc.).Diet samples were also submitted for analysis of DM, crude fiber, ash, and ether extract (Ward Laboratories, Inc., Kearney, NE).
Pens of pigs were weighed and feed disappearance was measured at the beginning and at the end of each experiment to determine ADG, ADFI, and F/G.The total grams of SID Val intake based on formulated values were divided by total BW gain to calculate the g of SID Val intake per kilogram of gain.
For the economic evaluation, total feed cost per pig, cost per lb of gain, revenue, and income over feed cost (IOFC) were calculated.The total feed cost per pig was calculated by multiplying the ADFI by the cost per lb of feed and the number of days.Cost per lb of gain was calculated by dividing the total feed cost per pig by the amount of pounds gained overall.Revenue per pig was calculated by multiplying the ADG times the total days in the trial times a live price of $0.60/lb.To calculate IOFC, total feed cost per pig was subtracted from pig revenue.Corn was valued at $3.60/bu ($129/ton), DDGS at $180/ton, soybean meal at $340/ton, L-Lysine HCl at $0.71/lb, L-Tryptophan at $11.00/lb, and L-Valine at $7.00/lb.The cost per ton of feed was considered fixed for Val:Lys levels below 65%.
For the statistical analysis, initially, responses measured at the pen level were analyzed using a general linear mixed model.Within each experiment, linear and quadratic polynomial contrasts with coefficients adjusted for unequally spaced treatments were used to evaluate the dose response effect of increasing dietary SID Val:Lys ratio on ADG, ADFI, F/G, BW, grams of SID Val intake per day, grams of SID Val intake per kg of gain, feed cost/pig, feed cost/lb of gain, total revenue/pig, and IOFC.Heterogeneous residual variances as a function of the response variables were fitted as needed.Model assumptions were checked and considered to be appropriately met.The experimental data were analyzed using the GLIMMIX procedure of SAS (SAS Institute Inc., Cary, NC).Prior to fitting the requirement estimation models, a base model was fit to estimate and assess variance components of weight block, weight block nested within experiment, and treatment by experiment interaction for each of the response variables.Subsequently, initial BW was tested as a covariate for each of the response variables.Linear and non-linear regression models adapted from Robbins et al. ( 2006) 6 were expanded to accommodate random effects and were fitted to ADG, F/G, feed cost per lb of gain, and IOFC to further estimate SID Val:Lys ratio requirements using an inverse prediction strategy.Specifically, competing statistical models fitted to the data were: a broken-line linear ascending (BLL) model, a broken-line quadratic ascending (BLQ) model, and a quadratic polynomial (QP).Broken-line regression models were fitted using the NLMIXED procedures of SAS.The optimization technique used was the dual Quasi-Newton algorithm, as specified by default in the NLMIXED procedure.Competing statistical models were compared using maximum-likelihood-based fit criteria, specifically the Bayesian information criteria (BIC).Results were considered significant at P ≤ 0.05.

Results and Discussion
The analyzed total amino acids, DM, CP, crude fiber, ether extract and ash contents of the experimental diets were reasonably consistent with formulated estimates (Tables 3  and 4).
In Exp. 1, ADG increased (linear, P = 0.009) with increasing SID Val:Lys ratio whereas ADFI only marginally increased (linear, P = 0.098) with no impact on F/G (Table 5).Final BW marginally increased (linear, P = 0.064) with increasing SID Val:Lys ratio.Grams of SID Val intake per day and grams of SID Val per kg of gain increased (linear, P < 0.001) with increasing SID Val:Lys ratio.Feed cost per pig, feed cost per lb of gain, and total revenue per pig increased (linear, P < 0.009) with increasing SID Val:Lys ratio with no evidence for differences in IOFC.
For feed cost per lb of gain, the overall best-fitting model was a QP (BIC: 914.5) compared with BLL and BLQ models (BIC: 919.3 and 921.8, respectively).The estimated regression equation for the best-fitting QP model (Fig. 3) was: QP equation for feed cost per lb of gain = 0.389 -0.643 × (SID Val:Lys) + 0.567 × (SID Val:Lys) 2 + 0.0005 × (Initial BW) Based on the best-fitting QP model, the minimum mean feed cost per lb of gain was estimated at less than 57.0%SID Val:Lys ratio.
Target performance levels based on the best fitting models for ADG and F/G are listed in Table 7.Note that at 97% of the optimum performance, the SID Val:Lys ratio for ADG and F/G is approximately 66 and 60%, respectively, whereas at 99% of the optimum performance, the SID Val:Lys ratio for ADG and F/G is approximately 69% and 64 to 65.5%, respectively.
In conclusion, the SID Val:Lys ratio to optimize performance ranged from 71.0% for minimum F/G to 74.4% for maximum ADG.However, feed cost per lb of gain was minimized at less than 57% SID Val:Lys and maximum income over feed cost was estimated at 62.3% SID Val:Lys with a plateau thereafter.Therefore, 99% of the optimum ADG and F/G were estimated at approximately 69% and 65% SID Val:Lys, respectively.  Diet samples were taken from six feeders per dietary treatment 3 d after the beginning of the trial and 3 d prior to the end of the trial and stored at -20°C, then CP and amino acid analysis was conducted on composite samples by Ajinomoto Heartland, Inc. (Chicago, IL).Samples of the diets were also submitted to Ward Laboratories, Inc. (Kearney, NE) for analysis of DM, crude fiber, Ca, P, ash and crude fat.
2 Values in parentheses indicate those calculated from diet formulation and are based on values from NRC (2012), with the exception of CP and total amino acid content from corn, soybean meal, and dried distillers grains with solubles; which were analyzed prior to diet formulation by Ajinomoto Heartland, Inc.

Figure 4 .
Figure 4. Fitted broken-line linear (BLL) regression model with income over feed cost (IOFC) as a function of increasing standardized ileal digestible (SID) Val:Lys ratio in 55 to 100 lb pigs.The maximum mean IOFC was estimated at 62.3% (95% CI: [58.5, 66.2]%) SID Val:Lys ratio.Each point represents a pen of pigs.

Table 1 .
Diet composition (as-fed basis; Exp 1) 1 1 Diets were fed from 68.9 to 99.0 lb BW.Corn, dried distillers grains with solubles (DDGS), and soybean meal were analyzed for CP and total amino acid concentrations and NRC (2012) SID digestibility values were used in the diet formulation.These diets were blended to make the intermediate dietary treatments: 62.5, 65.9, 69.6, and 73.0, SID Val:Lys. 2 OptiPhos 2000 (Huvepharma, Peachtree, GA) provided 227 phytase units (FTU) per lb of diet.1 Diets were fed from 56.0 to 89.7 lb BW.Corn, dried distillers grains with solubles (DDGS), and soybean meal were analyzed for CP and total amino acid concentrations and NRC (2012) SID digestibility values were used in the diet formulation.These diets were blended to make the intermediate dietary treatments:60.6, 63.9, 67.5, 71.1,  and 74.4 SID Val:Lys.  xtra PHY (DuPont, Wilmington, DE) provided 150 phytase units (FTU) per lb of diet.

Table 4 .
Chemical analysis of the diets (as-fed-basis; Exp. 2) 1 Diet samples were taken from six feeders per dietary treatment 3 d after the beginning of the trial and 3 d prior to the end of the trial and stored at -20°C, then CP and amino acid analysis was conducted on composite samples by Ajinomoto Heartland, Inc. (Chicago, IL).Samples of the diets were also submitted to Ward Laboratories, Inc. (Kearney, NE) for analysis of DM, crude fiber, Ca, P, ash and crude fat.2Values in parentheses indicate those calculated from diet formulation and are based on values from NRC (2012), with the exception of CP and total amino acid content from corn, soybean meal, and dried distillers grains with solubles, which were analyzed prior to diet formulation by Ajinomoto Heartland, Inc. 1

Table 5 .
Effects of standardized ileal digestible (SID) Val:Lys ratio on the growth performance and economics of finishing pigs from 70 to 100 lb, Exp. 1 1,2 PIC 337 × 1050, initially 68.8 lb BW) were used in a 19-d growth trial with 27 pigs per pen and seven pens per treatment.2Cornwasvaluedat $3.60/bu ($129/ton), DDGS at $180/ton, soybean-meal at $340/ton, and L-Valine at $7.00/lb. 3ed cost/lb gain = total feed cost divided by total gain per pig.Cost per ton used was not considering processing costs.4Onepound of live gain was considered to be worth $0.60.Total revenue/pig = total gain/pig × $0.60. 5Income over feed cost = total revenue/pig -feed cost/pig.

Table 7 .
Standardized ileal digestible (SID) Val:Lys ratio at different target performance levels of growing pigs Percent of optimum performance, %