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The effects of diet blending and feed budgeting on finishing pig growth performance, carcass characteristics, and economic return

August 1, 2014

Nelssen, J L



ABSTRACT

Three experiments were conducted to compare different phase-feeding regimens with blending diets using an automated feed-delivery system (FeedPro; Feedlogic Corp., Willmar, MN) for finishing pigs on growth performance, carcass characteristics, and economic return. In Exp. 1 and 2, a total of 1,091 pigs and 19 replicate pens per treatment were used to compare phase feeding 4 diets to blending a highand low-Lys complete diet to a set Lys curve and blending ground com and a complete supplement to match diet composition within phases. Blending corn and a complete supplement resulted in poorer (0.338 vs. 0.348; P < 0.04) G:F than in curve-fed pigs in both experiments and reduced (92.5 vs. 95-4 kg; P < 0.03) HCW compared with standard phase feeding during Exp. 2. Pigs fed to a Lys curve had decreased (P < 0.05) ADG and ADFI in Exp. 2 compared with standard phase-fed pigs, but overall feed costs were also the lowest (P < 0.01) for curve-fed pigs. However, no differences in income over feed cost were detected between treatments. In Exp. 3, 252 pigs with 9 replicate pens per treatment were used to evaluate phase feeding 4 diets compared with feeding diets blended on a Lys curve or phase feeding diets overand under-budgeted by 20% in each phase. Growth and carcass characteristics were similar across treatments, but curve pigs had the lowest, feed cost ($81.03 vs. $85.59; P < 0.03). These studies show that feeding a corn-supplement blend resulted in poorer performance, feeding to a Lys curve resulted in lower feed costs, and overand underbudgeting feed by 20% did not influence overall growth rate or economic return.

Key words: feed blending, feed budgeting, finishing pig, growth, phase feeding

INTRODUCTION

The swine industry has evolved from feeding as little as a single diet during the finishing period to more extensive programs using up to 7 diets; however, optimal nutrient concentrations vary with changes in lean growth and live weight, so there are frequently periods when the diet being fed is supplying excess nutrients (Moore and Mullan, 2009). In growing and finishing pigs, the rate of protein accretion in relation to live weight is curvilinear, increasing to a maximum then decreasing over time (Thompson et ah, 1996). Additionally, feed intake increases further reduce nutrient requirements, and, as a result, amino acid concentrations are generally reduced in the diet as the pig becomes heavier. By more accurately matching the change in pig nutrient requirements with age and physiological state, N and P excretion can be decreased without reducing performance (Jongbloed and Lenis, 1992; Honeyman, 1996; Paik et al., 1996). Increasing the number of feeding phases was previously demonstrated to have economic and environmental benefits (Van der Peet Schwering et ah, 1999; Pomar et al., 2007; Pomar et al. 2009), but in traditional systems these benefits have been shown to have a diminishing rate of return because of simultaneous increases in management and feed-storage costs (Boland et al., 1999).

Blend feeding, which involves mixing and delivering 2 diets in proportionate ratios, may provide feed-cost savings. A general trend for increasing average slaughter weights may also augment the cost benefits of phase feeding; Fowler (1984), Bikker et al. (1996), and Gill (1999) have shown that there is greater scope for reducing protein supply with increasing BW. The primary objective of the current research was to determine the effects of daily blending complete diets to a predetermined Lys curve compared with conventional phasefeeding strategies in finishing pigs. A secondary objective was to determine growth and economics of overor under-budgeting a standard phasefeeding program.

MATERIALS AND METHODS

General

All practices and procedures used in these experiments were approved by the Kansas State University Institutional Animal Care and Use Committee. Experiments 1 and 3 were conducted at the Kansas State University Swine Teaching and Research Center in Manhattan. Pigs were housed in 1 of 2 identical rooms within the research barn, which contained 40 pens (2.4 x 3.1 m) with adjustable gates facing the alleyway, allowing for continuous provision of 0.93 m2/pig. Each pen was equipped with a cup waterer and a single-sided, dry self-feeder with 2 eating spaces (Farmweid, Teutopolis, IL) located in the fence line. Pens were located over a completely slatted concrete floor with a 1.2-m pit underneath for manure storage. Experiment 2 was conducted at a commercial research finishing facility in southwestern Minnesota. The facility was double-curtain sided with completely slatted flooring. The barn contained 48 pens (3.05 x 5.49 m) equipped with a 5-hole conventional dry feeder (STACO Inc., Schaefferstown, PA) and a cup waterer to allow ad libitum consumption of feed and water. In both research facilities, an automated FeedPro feeding system (Feedlogic Corp., Willmar, MN) was used to deliver and record feeding amounts on an individual pen basis.

In all 3 trials, feed cost was calculated as the sum of individual diet cost plus grinding, mixing, and delivery (GMD) costs. The individual components of the GMD charges used were (1) grinding = $5.50/t, (2) mixing = $3.30/t, and (3) delivery = $7.70/t. In Exp. 1 and 2, the complete diets used in the standard and curve treatments received all 3 GMD charges. For the corn-supplement treatment, grinding was charged to the ground corn, mixing was charged to the supplement, and delivery was charged to both components. For Exp. 3, all treatments were charged with all GMD charges. Feed cost per pig and per kilogram of gain was calculated for each phase and the overall period of the experiment. Total revenue and income over feed cost (IOFC) were also determined within each experiment using a carcass price of $1.99/ kg and current ingredient costs. Total revenue was influenced by sort loss discounts and grade premiums assigned on a per-pig basis by the abattoir based on a pricing matrix calculated using HCW and lean meat yield. The average feed cost was subtracted from the derived pig revenue to attain the IOFC per pen. All monetary values used in this paper are expressed as US dollars.

Exp. 1

A total of 283 mixed-sex pigs (TR4 x 1050; PIC, Hendersonville, TN; initial 35.0 ± 0.6 kg of BW) were used in a 97-d trial to compare phasefeeding regimens. Pens were allotted to 1 of 3 experimental treatments using a completely randomized design. Each treatment had 12 replicate pens and 8 pigs per pen (4 barrows and 4 gilts). The 3 experimental treatments were (1) a standard 4-phase complete feeding program (standard), (2) blending a highand low-Lys complete diet over the entire experiment (curve), and (3) blending ground corn and a complete supplement within each phase (corn supplement). For the standard 4-phase feeding program, 4 finishing diets (Table 1) were formulated to provide 2.72, 2.30, 2.00, and 1.81 g of standardized ileal digestible (SID) Lys/Mcal of ME and were fed from 35 to 55 (d 0 to 21), 55 to 80 (d 21 to 42), 80 to 100 (d 42 to 71), and 100 to 126 kg of BW (d 71 to 97) for phases 1 to 4, respectively. For the curve treatment, a complete highand low-Lys diet was formulated to provide 3.15 and 1.63 g of SID Lys/ Meal of ME, respectively. The complete highand low-Lys diets were blended in varying ratios on a daily basis (Figure 1) to meet an SID Lys requirement curve, which was set using previously documented feed intake data collected using the FeedPro system in this facility. For the cornsupplement treatment, 4 complete supplements were formulated (Table 2) and stored separately from ground corn in feed-storage bins. The FeedPro system blended ground corn and the complete supplement in calculated ratios to be identical in dietary nutrient composition to those fed the standard phase-feeding program for each growing phase (Table 3). The SID Lys: ME ratios (g/Mcal) that were fed to pigs in each of the 3 treatments is shown in Figure 2. The figure illustrates the stair-step reduction of SID Lys:ME ratios used for the standard and corn-supplement treatments and the more gradual reduction in SID Lys:ME ratio for the curve treatment. The gradual reduction in SID Lys:ME ratio was achieved by changing the blending ratio on a daily basis. All complete diets, ground corn, and supplements were manufactured at the Kansas State Animal Science Feed Mill and were formulated to meet or exceed all nutrient requirement estimates (NRC, 1998).

Pigs were weighed and feed disappearance was determined at the end of each phase to calculate ADG, ADFI, and G:F (Table 4). At the end of the trial, pigs were weighed and transported (approximately 204 km) to an abattoir (Triumph Foods Inc., St. Joseph, MO). Pigs had been individually tattooed according to pen number to allow for data retrieval by pen and carcass data collection at the abattoir. Hot carcass weights were measured immediately after evisceration, and each carcass was evaluated for percentage yield, back fat, and loin depth (Table 5). Percentage yield was calculated by dividing HCW by live BW obtained at the farm before transport to the abattoir. Fat depth and loin depth were measured with an optical probe (SFK Technology, Herlev, Denmark) inserted between the third and fourth ribs located anterior to the last rib at a distance approximately 7.1 cm from the dorsal midline. Percentage lean was calculated according to NPPC (1991) equations for lean-containing 5% fat, where lean (5% fat)` - {2.83 + [0.469 x (0.4536 x HCW)] - [18.47 x (0.0394 x fat depth)] + [9.824 x (0.0394 x loin depth)]/(0.4536 x HCW)}. Grade premiums and sort loss discounts were also used to accurately determine the net revenue generated per pig.

Exp. 2

A total of 808 mixed-sex pigs (337 x 1050, PIC; initially 35.5 ± 0.7 kg of BW) were used in a 110-d trial to compare phase feeding with blending 2 complete finishing diets on a Lys curve in a commercial environment. Pens were randomly assigned to 1 of 3 treatments according to average BW within pen in a completely randomized design. There were 26 to 27 pigs per pen (no confounding due to random sex allocation) with 10 replicate pens per treatment. The 3 experimental treatments were (1) a standard 4-phase complete feed program (standard), (2) blending a highand low-Lys complete diet (curve), and (3) blending ground corn and a complete supplement within each phase (corn supplement). For the standard 4-phase feeding program, 4 finishing diets (Table 6) were formulated to provide 2.83, 2.59, 2.32, and 2.05 g of SID Lys/Mcal of ME and were fed from 35 to 52 (phase 1), 52 to 71 (phase 2), 71 to 86 (phase 3), and 86 to 108 kg (phase 4), respectively.

For the curve treatment, a complete highand low-Lys diet was formulated to provide 2.98 and 1.93 g of SID Lys/Mcal of ME, respectively. The complete highand low-Lys diets were blended in different ratios daily (Figure 3) to meet a SID Lys requirement curve that was configured using previously determined SID Lys requirements in this facility with the same genetics. For the corn-supplement treatment, complete supplements were manufactured (Table 7) by phase, and the FeedPro system blended ground corn and the complete supplement in calculated ratios to be identical in dietary nutrient composition to the standard phase-feeding program for each growing phase. Figure 4 illustrates the stair-step reduction of SID Lys:ME ratios used for the standard and corn-supplement treatments and the more gradual reduction in SID Lys:ME ratio for the curve treatment. The gradual reduction in SID Lys:ME ratio was achieved by changing the ratio of the 2 diets provided on a daily basis. All complete diets, ground corn, and supplements were manufactured at the Kansas State Animal Science Feed Mill and were formulated to meet or exceed all nutrient requirements (NRC, 1998).

A common complete diet containing 5.0 mg/kg of ractopamine HCl (RAC; Paylean, Elanco Animal Health, Greenfield, IN) was fed to all 3 treatments for 22 d from 108 to 127 kg of BW immediately before marketing. This diet was formulated to contain 2.67 g of SID Lys/Mcal of ME.

All complete diets, ground corn, and supplements were manufactured at the New Horizons Feed Mill (Pipestone, MN) and were formulated to meet all requirement estimates (NRC, 1998). Feed samples of each treatment were collected from several feeders at a single time point within each dietary phase. These samples were homogenized and analyzed for Lys content (AOAC 982.30 Ea,b, chp. 45.3.05; AOAC, 2006) at the University of Missouri Agricultural Experiment Station Chemical Laboratories (Columbia; Table 8).

Pigs from each pen were weighed as a group, and feed disappearance was determined approximately every 21 d to determine ADG, ADFI, and G:F (Table 9). On d 88 of the experiment, the 4 heaviest pigs from each pen (determined visually) were weighed and removed in accordance with the normal marketing procedure of the farm. On d 110, pigs were transported (approximately 95 km) to a commer- cial abattoir (JBS Swift and Company, Worthington, MN) for processing. Pigs had been individually tattooed according to pen number to allow for data retrieval by pen and carcass data collection at the abattoir. Hot carcass weights were measured immediately after evisceration, and each carcass was evaluated for percentage yield, back fat, and loin depth (Table 10). Percentage yield was calculated by dividing HCW by live BW obtained at the farm before transport to the abattoir. Fat depth and loin depth were measured with an optical probe (SFK Technology) inserted between the third and fourth ribs located anterior to the last rib at a distance approximately 7.1 cm from the dorsal midline. Fat-free lean index (FFLI) was calculated using NPPC (2000) guidelines for carcasses measured with the Fat-O-Meater (SFK Technology) such that FFLI = {15.31 + [0.51 x (0.4536 x HCW)] - [31.277 x 0.0394 x last-rib fat thickness)] + [3.813 x (0.0394 x loin muscle depth)]/(0.4536 x HCW)}. Grade premiums and sort loss discounts were included to accurately determine the net revenue generated per pig (Table 11). As a result of misidentification of pigs by abattoir personnel, of the original 10 replicates per treatment, carcass data could be obtained for 6 pens from the standard treatment, 10 pens from the curve group, and 7 pens from the corn-supplement treatment.

Exp. 3

A total of 252 mixed-sex pigs (327 x 1050, PIC; initial BW = 36.2 ± 0.4 kg of BW) were used in a 95-d trial to compare feed-budgeting strategies and blending 2 complete finishing diets on a Lys curve on growth performance, carcass characteristics, and economics. Pens were allotted to 1 of 4 experimental treatments using a randomized complete block design. Each treatment had 9 replicate pens and 7 pigs per pen (4 gilts and 3 barrows per pen). The 4 experimental treatments were ( 1 ) a standard 4-phase complete feed program (standard), (2) blending a highand low-Lys complete diet over the entire experiment (curve), (3) treatment 1 diets with 20% greater feed budget for phases 1, 2, and 3 (over-budgeted), and (4) treatment 1 diets with 20% lower feed budget for phases 1, 2, and 3 (under-budgeted). All diets were dispensed using the FeedPro system and provided ad libitum access to feed. For the standard 4-phase feeding program as well as the over-budgeted and under-budgeted treatments, 4 finishing diets (Table 12) were formulated to provide 2.72, 2.30, 2.00, and 1.81 g of SID Lys/ Meal of ME.

The FeedPro system was programmed to deliver a predetermined amount of feed from each diet to each pen and to automatically update allotted budgets when pigs were removed due to death or illness. Pigs fed the standard treatment were programmed to receive a set feed budget of 53.1, 62.6, 72.7, and 79.4 kg for diets 1 to 4, respectively. Pigs fed the overand under-budgeted treatments were assigned feed budgets 20% higher and 20% lower than their standard counterparts for phases 1, 2, and 3, with phase 4 fed for the remainder of the trial after the phase-3 diet was consumed. When budgeted allotment of each phase was exhausted for the over-budgeted and under-budgeted treatments, the FeedPro system automatically switched phases on an individual pen basis.

Pigs from all treatments were weighed and feed disappearance was recorded on the date of phase changes for the standard treatment to establish equal periods for data compari- son. Measurements of ADG, ADFI, and G:F were calculated at each of these phase changes (Table 13). Based on the feed budgeted for the standard treatment, the data periods were d 0 to 23 (phase 1), 23 to 49 (phase 2), 49 to 72 (phase 3), and 72 to 95 (phase 4).

For the curve treatment, a complete high-Lys and low-Lys diet was formulated to provide 2.97 and 1.75 g of SID Lys/Mcal of ME, respectively. The complete highand low-Lys diets were blended in varying ratios on a daily basis (Figure 5) to meet an SID Lys requirement curve, which was set using previously documented feed-intake data in this facility. The SID Lys:ME ratios (g/Mcal) provided by the 4 feeding programs to pigs throughout the finishing period are shown in Figure 6, which illustrates the stair-step reduction of SID Lys: ME ratios used for the differ- ent phase-feeding treatments and the more gradual reduction in SID Lys:ME ratio for the diet-blending treatment. The gradual reduction in SID Lys:ME ratio was achieved by changing the ratio of the 2 diets provided on a daily basis. Feed was manufactured, sampled, and analyzed as in Exp. 1 and 2 (Table 14).

On d 84, pigs were weighed and transported (approximately 204 km) to an abattoir (Triumph Foods Inc.). Pigs were individually tattooed according to pen number to allow for data retrieval by pen and carcass data collection at the abattoir. Standard carcass criteria of percentage carcass yield, HCW, back fat depth, loin depth, and percentage lean were measured (Table 15). Hot carcass weights were measured immediately after evisceration, and percentage yield was calculated by dividing HCW by live BW obtained at the farm before transport to the abattoir. Carcass trait measurements were calculated as in Exp. 1, and grade premiums and sort loss discounts were included to accurately determine the net revenue generated per pig (Table 16).

Statistical Analysis

In Exp. 1, data were analyzed as a completely randomized design using PROC GLM in SAS (SAS Institute Inc., Cary, NC). Experiments 2 and 3 used PROC MIXED in SAS for data analysis. Experiment 2 was analyzed as a completely randomized design, and Exp. 3 was analyzed as a randomized complete block design with treatments randomly assigned to blocks throughout the barn. In all 3 experiments, HCW was used as a covariate for fat depth, loin depth, lean percentage, and FFLI. When treatment effect was a significant source of variation, means were separated using the PDIFF option of SAS in Exp. 1 and 2 and by preplanned CONTRAST statements in Exp. 3. Least squares means were calculated for each independent variable. Statistical significance was set at P < 0.05 and trends at P < 0.10 for all statistical tests.

RESULTS AND DISCUSSION

Diet Analysis

Diet samples collected for Exp. 1 were lost and therefore not available for analysis. The analyzed Lys levels for standard and curve regimens in Exp. 2 confirm the decreasing Lys content over the growing period and are within permitted analytical variation limits according to AAFCO (2005); however, the analyzed Lys levels for the corn-supplement blend varied more greatly compared with formulated levels than for standard and curve treatments (Table 7), suggesting that there either may have been sampling error or the FeedPro system could have inaccurately blended the corn and supplement. Analyzed Lys levels in diets from Exp. 3 are in general agreement with formulated Lys content.

Exp. 1

Average daily gain and pig BW were similar (P > 0.12) across treatments in each of the 4 phases. In phases 1 to 3, ADFI was also similar (P > 0.14), but in phase 4, pigs fed using curve diets had lower (P < 0.03) ADFI than pigs fed using standard phase feeding of complete diets or the corn-supplement blend. For feed efficiency, during phase 1 (35 to 55 kg) pigs fed the corn-supplement blend had greater (P < 0.03) G:F than pigs fed standard or curve diets; however, G:F was poorer (P < 0.05) in pigs fed the corn-supplement blend in phase 3 (80 to 100 kg) than in pigs fed standard or curve diets. In phase 4 (100 to 126 kg), pigs fed curve diets had poorer (P < 0.04) G:F than pigs fed using standard phase feeding of either complete diets or the ground corn-supplement blend. Overall (35 to 126 kg), ADG, ADFI, and final BW were similar (P > 0.14) across treatments, but pigs fed the cornsupplement blend had poorer (P < 0.01) G:F than pigs fed curve diets and tended to have poorer (P < 0.09) G:F than pigs fed using the standard program.

For carcass characteristics, no differences were detected (P > 0.18) in HCW, percentage yield, or loin depth across treatments. Pigs fed using the corn-supplement blend had greater (P < 0.03) percentage lean and lower (P < 0.04) fat depth than pigs fed using standard phase-fed diets or curve diets blended using the FeedPro system.

Feeding curve diets tended (P < 0.07) to result in feed savings ($2.59/ pig) versus the standard phase-feeding program. The majority of the difference for curve and standard diets was due to lower ADFI and better G:F observed in phase 4, which resulted in $1.44 reduction (P < 0.01) in feed cost per pig. For the ground cornsupplement blend, cost of mixing ($3.30/t) was not assessed for ground corn, which contributed to lower GMD cost and numerically lower feed costs per pig. Feed cost per kilogram of gain was lower (P < 0.01) for pigs fed the corn-supplement blend in phase 1 and lower (P < 0.03) for the curve diet in phases 3 and 4, but no overall differences (P > 0.11) were observed across the treatments. No (P > 0.41) differences were observed in total revenue or IOFC across all treatments.

Exp. 2

In phase 1 (35 to 52 kg) and phase 2 (52 to 71 kg), growth performance and pig BW were similar (P > 0.13) across all treatments. For phase 3 (71 to 86 kg), ADG, G:F, and pig BW were not influenced (P > 0.18) by blending treatments, but pigs fed diets blended on a Lys curve had lower (P < 0.01) ADFI than pigs fed either standard phase diets or those fed a corn-supplement blend. In phase 4 (86 to 108 kg), pigs fed the corn-supplement blend had poorer (P < 0.04) ADG than pigs fed either standard phase-feeding or blended diets on a Lys curve. In addition, pigs fed standard diets had improved (P < 0.02) ADFI compared with pigs fed curve diets or a corn-supplement blend; however, pigs fed curve diets had increased (P < 0.03) G:F compared with pigs fed the cornsupplement blend, with standard pigs intermediate. For BW in phase 4, pigs fed standard diets were heavier (P < 0.02) than pigs fed curve diets and tended to be heavier (P < 0.02) than those fed the corn-supplement blend. Within the overall trial period (35 to 108 kg), pigs fed standard diets had greater (P < 0.02) ADG compared with both blending treatments and had greater ADFI (P < 0.01) than pigs fed a curve diet, with those fed a corn-supplement blend intermediate. However, pigs fed curve diets had improved (P < 0.04) G:F compared with other treatments. During phase 5 (108 to 127 kg), in which all pigs were fed a common diet containing ractopamine HC1, pigs previously fed the corn-supplement blended diets had greater (P < 0.02) ADFI than those previously fed curve diets. In addition, pigs formerly fed standard phase diets tended to be heavier (P < 0.10) than pigs formerly fed a ground corn-supplement blend.

Over the entire finishing period (35 to 127 kg), pigs fed standard diets had greater (P < 0.04) ADG than pigs fed either curve diets or a corn-supplement blend, and pigs fed standard diets or a corn-supplement blend had greater (P < 0.05) ADFI than curve pigs. Pigs fed curve diets, however, had improved (P < 0.04) G:F compared with pigs fed a cornsupplement blend. For carcass characteristics, no differences were observed (P > 0.22) in percentage yield, FFLI, back fat depth, or loin depth across all treatments, but pigs fed standard diets had heavier (P < 0.03) HCW than pigs fed a corn-supplement blend and tended to have heavier (P < 0.07) HCW than those fed curve diets.

Higher ADG and ADFI for pigs fed standard diets led to greater (P < 0.01) feed cost per pig compared with curve pigs and a trend (P < 0.08) for higher feed costs compared with pigs fed the corn-supplement blend. Because standard pigs experienced greater gain, however, feed cost per kilogram of gain was similar (P > 0.10) across all treatments overall and for most individual phases. Furthermore, no differences were observed (P>0 .15) in total revenue per pig. Although IOFC did not differ (P > 0.15) across treatments, pigs fed diets blended to a Lys curve had a $1.80 and $3.11 advantage in IOFC over standard and corn-supplement treatments, respectively.

Exp. 3

Although pen weights and feed disappearance were recorded on d 23, 49, 72, and 95 according to average phase changes in the standard treatment, phase changes in the overand underbudgeted treatments took place when allotted feed budgets were exhausted on a per-pen basis. In the over-bud- geted treatment, the average dates of diet change were d 29, 56, and 83 for phases 2, 3, and 4, respectively. In the under-budgeted treatment, the average dates of diet changes were d 18, 42, and 61 for phases 2, 3, and 4, respectively.

In phase 1 (d 0 to 23), ADG was lower (P < 0.04) in pigs fed the curve treatment compared with each of the 3 phase-fed programs. Although no differences (P > 0.47) in ADFI were seen across treatments, pigs fed the curve diet had poorer (P < 0.04) G:F than pigs fed overand under-budgeted phase-feeding programs. Although ADG was similar (P > 0.16) across all treatments during phase 2 (d 23 to 49), under-budgeted pigs had higher ADFI (P < 0.05) than curve pigs and poorer (P < 0.05) G:F than pigs fed standard or curve diets. In phase 3 (d 49 to 72), pigs in the phase and under-budgeted treatments had greater (P < 0.05) ADG than pigs fed the over-budgeted treatment, with curve-fed pigs intermediate. Average daily feed intake was similar ( P > 0.18) across treatments in phase 3, but pigs fed the under-budgeted treatment had improved (P < 0.05) G:F compared with pigs that were overbudgeted for each phase. In phase 4 (d 72 to 95), no differences (P > 0.13) were observed in ADG, ADFI, or G:F across treatments. Overall (d 0 to 95), no differences (P > 0.11) were detected in ADG, ADFI, G:F, or final BW across treatments.

For carcass characteristics, there was a trend (P = 0.09) for pigs fed the standard phase-feeding program to have higher-yielding carcasses than pigs over-budgeted or fed to a Lys curve. This result was driven by a trend (P = 0.10) for heavier HCW in pigs fed the standard rather than curve treatments. Across treatments, no differences (P > 0.14) were observed in percentage lean, fat depth, or loin depth.

Feeding diets blended to a Lys curve resulted in the lowest (P < 0.03) feed costs in phases 2 and 3 and overall, resulting in average feed savings per pig of $4.09 compared with the 3 phase-feeding strategies. For feed cost per kilogram of gain, feeding curve diets resulted in higher (P < 0.03) costs compared with pigs fed over-budgeted diets during phase 1, with standard and under-budgeted treatments intermediate. Conversely, in phase 2 curve diets resulted in the most economical weight gain (P < 0.001) and in phase 3 pigs fed curve and under-budgeted diets had lower (P < 0.04) feed cost per kilogram of gain than those overbudgeted. Overall, delivering diets to a Lys curve resulted in lower (P < 0.01) cost per kilogram of gain than over-budgeting and tended (P < 0.06) to be lower than standard and under-budgeted treatments. Total revenue received per pig tended (P < 0.10) to be higher ($5.37/pig) for pigs fed standard diets compared with curve or under-budgeted treatments. This advantage was mainly due to the advantage in ADG in standard pigs, which resulted in heavier HCW. Pigs phase-fed a correctly estimated feed budget (standard) tended (P < 0.09) to have higher IOFC than curve ($4.61 /pig) or over-budgeted ($4.55/pig) treatments, whereas pigs fed under-budgeted diets performed similarly (P > 0.49) to their standard phase-fed counterparts, sacrificing just $1.81 per pig.

With the advent of onsite computer programming and feed-delivery systems that can blend and deliver diets daily, the capability of modern feeding technology has radically evolved in recent years. These advances allow producers to exploit nutritional science that has been known for years, such as the decrease in Lys:ME requirements over the course of the growing period (Gill, 1999). Blending base diets daily according to known requirements offers potential benefits, including lower feed costs and the minimization of nutrient excretion while maintaining optimal growth performance. Although these perceived benefits are essential to the development of sustainable swine production systems (Honeyman, 1996), comprehensive evaluations of this practice using current technology on commercial farms are limited.

Although Pomar et al. (2007) reported faster growth rates for pigs fed using a daily Lys curve via an automated feed-delivery system compared with pigs fed a 3-phase diet, the results of the present study generally disagree, with consistent reductions in growth rate across all 3 experiments. The observed differences may be attributed to the fact that in Pomar et al. (2007), curve-fed pigs had greater total Lys intake than phase-fed pigs, whereas all pigs across treatments in the present study had similar Lys intake because phase-fed diets were formulated to SID Lys:ME ratios (Figure 2; Figure 4; Figure 6) that provided both an excess and shortage of nutrients based on expected requirements in each phase.

Overall feed efficiency improved in pigs fed diets blended to a Lys curve compared with those phase-fed a series of 4 diets, particularly in Exp. 1 and 2. Increasing the number of feeding phases in finishing has shown consistent improvements in feed efficiency (Lee et ah, 2000; Pomar et ah, 2007; Moore and Mullan, 2009), which corresponds with reductions in N and P excretion (Jongbloed and Lenis, 1992; van der Peet-Schwering et ah, 1999). The feed efficiency improvement for pigs fed blended diets resulted in net feed savings of $2.59, $4.07, and $4.56 per pig for Exp. 1, 2, and 3, respectively, an average approximate reduction of 4% in overall feed costs over phase-fed pigs. These feed savings resulted in numerical advantages in IOFC in Exp. 2, but due to reduced HCW in curve-fed pigs, greater IOFC did not result in Exp. 1 or 3. As noted by Moore and Mullan (2009), it is also important to consider that although diet blending using the FeedPro system can reduce feed costs, the reported feed costs do not account for the cost of purchasing, installing, and maintenance for the equipment required to implement feed blending.

Mixing ground corn and a complete supplement to provide diets equivalent to standard phase-feeding regimens is an additional avenue to use the feed-blending capabilities of the FeedPro system. In Exp. 1 and 2, corn-supplement blending resulted in poorer feed efficiency compared with blending diets to a Lys curve and reduced ADG compared with standard phase feeding. Feed cost per kilogram of gain for pigs fed the cornsupplement blend was almost as high as in standard pigs in both experiments, but net revenue suffered due to the numerically lighter HCW in the corn-supplement treatment. High feed costs combined with the lowest returns resulted in pigs fed the cornsupplement blend having the poorest IOFC in Exp. 1 and 2. Although diet samples could not be analyzed in Exp. 1, in Exp. 2 the variation in analyzed Lys content compared with formulated Lys levels for the cornsupplement blend was concerning. This variation may explain the poorer growth performance, particularly during the later stages of the growingfinishing period. Because the cornsupplement blend theoretically should have provided a diet equivalent to the standard program, the reason for this variation in Lys content remains unclear. Explanations could include sampling error, incorrect supplement nutrient levels, or inaccuracy of the FeedPro blending capabilities when handling diets differing in form and density. The accuracy of feed blending was determined using diets of similar texture upon installation of the FeedPro system at each facility, but future research evaluating similar blending strategies to verify the blending capability of the system with ingredients of different bulk densities would be prudent. Recent increases in feed ingredient costs within the United States livestock industry may reduce the practicality of 2-ingredient mixing strategies, such as cornsupplement blending, considering that modern diets are now incorporating a larger number of starch and protein sources than traditional corn-soy rations (Plain, 2007).

Evaluation of diet budgeting strategies in Exp. 3 revealed that overbudgeted diets may have restricted growth in the midand late-finishing period because of an oversupply of protein. Lenis (1989), Lee et al. (2000), and Garry et al. (2007) have shown that excess amino acids that cannot be used for body protein deposition have to be deaminated and excreted, resulting in deterioration in growth and feed efficiency. Conversely, under-budgeted diets supplied an SID Lys:ME ratio slightly below biological requirements throughout the duration of the experiment. Growth performance for under-budgeted pigs was slightly poorer during phases 1 and 2 (36 to 81 kg), but similar to standard pigs in the late finishing period (81 to 132 kg). Based on well-documented compensatory growth responses seen when feeding adequate protein in later growth periods (Wahlstrom and Libal, 1983), Main et al. (2008) suggested that as long as Lys requirements are met in late finishing, feeding slightly less than the Lys requirement in early finishing period may offer feed cost savings without forfeiting growth performance. Thus, if Lys requirements were accurately estimated, results of Exp. 3 suggest that under-budgeting by 20% can result in similar growth performance responses and potential feed-cost reductions. As additional efforts are made to minimize feed costs in the finishing phase, formulating early finishing diets slightly lower than the physiological needs of the pig may offer an opportunity to lower overall feed costs.

IMPLICATIONS

Feeding diets blended to a Lys curve can effectively reduce overall feed costs but may lead to reductions in growth performance. The reason growth performance in curve-fed pigs was consistently poorer than in phasefed pigs is unclear, and additional research may elucidate the underlying reasons. Although these experiments have shown the effectiveness of blending 2 base diets on finishing pig growth performance, evaluating the nutrient excretion of finishing pigs fed curve diets compared with phase feeding would be beneficial. Finally, overand under-feed budgeting did not significantly influence overall growth rate or economic return.

ACKNOWLEDGMENTS

Appreciation is expressed to Feedlogic Corp. (Willmar, MN) for supplying equipment and technical support and to New Horizons Farms (Pipestone, MN) for providing animals and research facilities.

1 Contribution no. 14-007-J from the Kansas Agricultural Experiment Station, Manhattan 66506-0210.

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H. L. Frobose,*2 R. C. Sulabo.f J. M. DeRouchey,* D. Ryder,f M. D. Tokach,* S. S. Dritz,§ R. D. Goodband,* PAS, and J. L. Nelssen*

'Department of Animal Sciences and Industry, College of Agriculture, Kansas State University,

Manhattan 66506-0210; fDepartment of Animal Sciences, College of Agricultural,

Consumer and Environmental Sciences, University of Illinois, Urbana 61801;

fFeedlogic Corp., Willmar, MN 56201; and §Department of Diagnostic Medicine/Pathobiology,

College of Veterinary Medicine, Kansas State University, Manhattan 66506-0210

2 Corresponding author: frobose@ksu.edu


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