The Effect of Phase-Feeding Strategies on Growth Performance The Effect of Phase-Feeding Strategies on Growth Performance and Carcass Characteristics of Growing-Finishing Pigs: II. Field and Carcass Characteristics of Growing-Finishing Pigs: II. Field Approach on Lysine Levels Approach on Lysine Levels

Summary The objective of this study was to evaluate phase-feeding strategies for grow-finish pigs under commercial research conditions and using a field approach with lysine levels slightly below the pig’s requirement estimates for maximum growth performance. A total of 1,100 pigs (PIC 359 × 1050; initially 57 lb body weight (BW)) were used in a randomized complete block design with 25 pigs per pen and 11 pens per treatment. Treatments consisted of four feeding programs: a 1-phase feeding program with 0.79% standardized ileal digestible (SID) lysine from 60 to 280 lb BW; a 2-phase feeding program with 0.91 and 0.72% SID lysine from 60 to 220 and 220 to 280 lb BW, respectively; a 3-phase feeding program with 1.07, 0.85, and 0.72% SID lysine from 60 to 110, 110 to 220, and 220 to 280 lb BW, respectively; and a 4-phase feeding program with 1.07, 0.91, 0.79, and 0.72% SID lysine from 60 to 110, 110 to 160, 160 to 220, and 220 to 280 lb, respectively. The lysine levels were determined based on the estimated lysine requirements to achieve 98.5% of maximum growth rate for the weight range in each phase, using an equation developed by the genetic supplier. The experimental diets were based on corn, distillers dried grains with solubles (DDGS), and soybean meal. Overall, from d 0 to 119, pigs fed the 1-phase feeding program had decreased ( P = 0.009) average daily gain (ADG


Introduction
Phase-feeding programs have been widely used to closely meet the nutrient requirements of grow-finish pigs and to reduce nutrient excretion in the environment. 3ccurate estimates of nutritional requirements are essential to develop phase-feeding strategies and to minimize the supply of nutrients in excess or deficiency.Moreover, performance is typically optimized by meeting the nutritional requirements for growth.However, in practice, formulating diets to closely meet the requirements might not be the most prevailing or economically advantageous approach.
Previous studies suggest that simplification of feeding strategies to fewer phases can maximize growth performance, carcass characteristics, and economics. 4,5,6,7,8This effect was particularly observed by using lysine levels at the requirement in either a 2-or 4-phase feeding program, 8 prompting further evaluation of phase-feeding strategies for grow-finish pigs.While a companion study evaluated phase-feeding strategies for grow-finish pigs using lysine levels at the requirement, the present study took a different approach by using lysine levels slightly below (approximately 98%) the requirement to maximize growth performance.
Therefore, the objective of this study was to evaluate phase-feeding strategies for growfinish pigs by determining the effects on growth performance, carcass characteristics, and economics.This study is the second of a series of two companion phase-feeding studies developed under commercial research conditions and focused on using a field approach with lysine levels slightly below the estimated requirements for maximum growth rate.Lee, J. H., Kim, J. D., Kim, J. H., Jin, J., Han, In K. 2000.Effect of phase feeding on the growth performance, nutrient utilization and carcass characteristics in finishing pigs.Asian-Aust J Anim Sci.13(8):1137-1146.5 O'Connell, M. K., Lynch P. B., O'Doherty, J. V. 2005.A comparison between feeding a single diet or phase feeding a series of diets, with either the same or reduced crude protein content, to growing finishing pigs.Anim Sci.81:297-303.6   Garry, B. P., Pierce, K. M., O'Dogerty, J. V. 2007.The effect of phase-feeding on growth performance, carcass characteristics and nitrogen balance of growing and finishing pigs.Irish J Agr Food Res.46:93-104.

Procedures
The Kansas State University Institutional Animal Care and Use Committee approved the protocol used in this experiment.The study was conducted at a commercial research facility in southwestern Minnesota.The barn was naturally ventilated and doublecurtain-sided.Each pen was equipped with a 4-hole stainless steel dry self-feeder and a cup waterer for ad libitum access to feed and water.Feed additions to each individual pen were made and recorded by a robotic feeding system (FeedPro, Feedlogic Corp.,  Wilmar, MN).
A total of 1,100 pigs (PIC 359 × 1050; initially 57 lb BW) were used in a 119-d growth trial with 25 pigs per pen and 11 pens per treatment.Pigs were allotted to treatments based on initial BW in a randomized complete block design.
The treatments consisted of four phase-feeding programs and were arranged in a 1-way treatment structure, including: a 1-phase feeding program with 0.79% SID lysine from 60 to 280 lb BW; a 2-phase feeding program with 0.91 and 0.72% SID lysine from 60 to 220 and 220 to 280 lb BW, respectively; a 3-phase feeding program with 1.07, 0.85, and 0.72% SID lysine from 60 to 110, 110 to 220, and 220 to 280 lb BW, respectively; and a 4-phase feeding program with 1.07, 0.91, 0.79, and 0.72% SID lysine from 60 to 110, 110 to 160, 160 to 220, and 220 to 280 lb, respectively (Table 1 and Figure 1).The equation used for lysine requirement estimates for finishing gilts in g/Mcal NE was: 0.000056 × BW 2 , lb -0.02844 × BW, lb + 6.6391, with estimated lysine levels set for 98.5% of maximum growth rate and 97.5% of maximum feed efficiency 9 for the weight range in each phase.
The diets were based on corn, DDGS, and soybean meal (Table 2).A withdrawal strategy to remove DDGS from the diet was applied in the last phase of the 2-, 3-, and 4-phase feeding programs.Lysine levels in experimental diets were achieved by altering the ratio of corn to soybean meal while keeping the amount of L-Lys HCl constant within phases.Diet samples from each phase were taken from 6 feeders per dietary treatment 3 d after the beginning and 3 d before the end of each phase and stored at -4°F.Composite samples were homogenized, subsampled, and analyzed for dry matter (DM), crude protein (CP), acid detergent fiber (ADF), neutral detergent fiber (NDF), ether extract, Ca, and P (Ward Laboratories Inc., Kearney, NE).Composite samples were also analyzed for total amino acid (AOAS method 994.12 for all except Trp and 994.13 for Trp) 10 by Ajinomoto Heartland, Inc. (Chicago, IL).
Pens of pigs were weighed and feed disappearance measured on d 0, 13, 34, 50, 61, 71,  85, 98, and 119 to determine ADG, ADFI, and F/G.On d 119, final pen weights were taken and pigs were tattooed with a pen identification number and transported to a USDA-inspected packing plant (JBS Swift and Co., Worthington, MN) for processing and carcass data collection.Carcass measurements included HCW, backfat, loin depth, and percentage lean.Percentage lean was calculated from a plant proprietary equation.Carcass yield was calculated by dividing the pen average HCW by the pen average final live weight obtained at the farm.
For the economic analysis, feed cost per pig, feed cost per lb of gain, revenue per pig, and IOFC were calculated on a pen basis.Corn was valued at $3.53/bu ($126/ton), soybean meal at $350/ton, DDGS at $176/ton, L-lysine at $0.75/lb, DL-methionine at $1.40/lb, L-threonine at $1.05/lb, and L-tryptophan at $8/lb.Feed cost per pig was calculated by multiplying the feed cost per lb by ADFI and by the number of days in each phase, then adding up the values of each phase.Feed cost per lb of gain was calculated by dividing the feed cost per pig by the overall weight gain.Revenue was obtained by multiplying carcass gain by an assumed value of $70 per cwt of carcass.The IOFC was calculated by subtracting the feed cost per pig from revenue per pig.
Data were analyzed using a linear mixed model with treatment as fixed effect, block as random effect, and pen as the experimental unit.Hot carcass weight was used as a covariate for analyses of backfat, loin depth, and lean percentage.Statistical models were fitted using the GLIMMIX procedure of SAS version 9.4 (SAS Institute Inc., Cary, NC).Results were considered significant at P ≤ 0.05.

Results and Discussion
The analyzed DM, CP, ADF, NDF, ether extract, Ca, P, and amino acid content of experimental diets (Table 3) were consistent with formulated estimates.
In Phase 1 (d 0 to 34), decreased ADG and poorer F/G were observed (P < 0.001) in pigs fed the 1-and 2-phase programs compared to those fed the 3-and 4-phase feeding programs, with the poorest performance observed in the 1-phase program.This response in growth performance was due to the lower lysine levels in 1-and 2-phase programs (0.79 and 0.91% SID Lys, respectively) compared to 3-and 4-phase programs (1.07%SID Lys).Consequently, pigs fed the 1-and 2-phase programs had lower (P < 0.001) BW than the other feeding programs at the end of Phase 1, with the lightest BW observed in pigs fed the 1-phase program.
In Phase 2 (d 34 to 61), decreased ADG and poorer F/G were observed (P < 0.001) in the 1-phase program compared to the other feeding programs.The impact on growth performance was again associated with the lower lysine levels in the 1-phase program (0.79% SID Lys) in comparison to the other feeding programs (0.85 and 0.91% SID Lys).Consequently, pigs fed the 1-phase program had the lowest (P < 0.001) BW at the end of Phase 2.
In Phase 3 (d 61 to 85), F/G was improved (P = 0.004) in pigs fed the 1-phase program compared to those fed the 3-and 4-phase programs, with the 2-phase program intermediate.The improvement in F/G in the 1-phase over the 4-phase program was observed even though the lysine level was the same (0.79% SID Lys).This suggests the occurrence of compensatory growth in pigs fed the 1-phase program following a period of low lysine intake in the previous phases.Although F/G was improved, pigs fed the 1-phase program had the lowest (P < 0.001) BW at the end of Phase 3.

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In Phase 4 (d 85 to 119), ADG was increased (P = 0.002) in pigs fed the 1-phase program compared to those fed the 2-and 3-phase programs, with the 4-phase program intermediate.Also, F/G was improved (P < 0.001) in pigs fed the 1-phase program compared to the other feeding programs.This response in growth performance was due to the higher lysine level in the 1-phase program (0.79% SID Lys) in comparison to the other programs (0.72% SID Lys), but may also be attributed to a compensatory growth improvement.
Overall (d 0 to 119), the 1-phase feeding program resulted in lower (P = 0.009) ADG compared to the 4-phase program, with 2-and 3-phase programs intermediate.The 1-, 2-, and 3-phase programs resulted in poorer (P < 0.001) F/G compared to the 4-phase feeding program, with the poorest F/G observed in the 1-phase program.There was no evidence for difference (P > 0.05) in ADFI across the feeding programs.Final BW and HCW were lower (P < 0.05) in pigs fed the 1-phase program compared to those fed the 4-phase program, with 2-and 3-phase programs intermediate.No evidence for differences (P > 0.05) was observed across the feeding programs for the carcass traits: yield, backfat thickness, loin depth, or percentage lean.
For economics, feed cost per pig was lower (P = 0.033) in the 1-phase feeding program compared to the 3-phase program, with 2-and 4-phase feeding programs intermediate.However, feed cost per lb of gain was lower (P = 0.006) in the 4-phase program compared to 2-and 3-phase programs, with the 1-phase feeding program intermediate.Revenue and IOFC per pig were increased (P < 0.05) in the 4-phase program compared to the 1-phase program, with 2-and 3-phase feeding programs resulting in intermediate values.
This study suggests that feeding a single diet throughout the grow-finish period compromises overall growth rate and both live and carcass weight as compared to phase-feeding.As a consequence, there is an impact on IOFC associated with the 1-phase feeding strategy.In contrast, previous studies have shown no effect on growth performance by feeding a single phase during the grow-finish period. 11,12,13,14This could be due to differences in lysine levels or weight range used in those studies, as well as genetic and experimental conditions.
This study also indicates that simplification of feeding programs to 2 or 3 dietary phases might have negative implications on overall feed efficiency and IOFC compared to a feeding program with 4 dietary phases.Previous research conducted by our group demonstrated that implementing a feeding program with either 2 or 4 dietary phases 11 Lee, J. H., Kim, J. D., Kim, J. H., Jin, J., Han, In K. 2000.Effect of phase feeding on the growth performance, nutrient utilization and carcass characteristics in finishing pigs.Asian-Aust J Anim Sci.13(8):1137-1146.
12 O'Connell, M. K., Lynch P. B., O'Doherty, J. V. 2005.A comparison between feeding a single diet or phase feeding a series of diets, with either the same or reduced crude protein content, to growing finishing pigs.Anim Sci.81:297-303.13 Garry, B. P., Pierce, K. M., O'Dogerty, J. V. 2007.The effect of phase-feeding on growth performance, carcass characteristics and nitrogen balance of growing and finishing pigs.Irish J Agr Food Res.46:93-104.

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in grow-finish led to similar growth performance, carcass characteristics, and IOFC. 15owever, in the previous study lysine levels were closely set to the requirements for 100% of maximum growth rate and 98.7% of maximum feed efficiency.In the present study, lysine levels were slightly below the requirements, with levels set for 98.5% of maximum growth rate and 97.5% of maximum feed efficiency.Apparently, feeding lysine levels slightly below the requirements seems to be sufficient to impact growth performance in phase-feeding programs with fewer dietary phases.
Feeding strategies with fewer dietary phases generally provide lysine levels below the requirements initially and rely on compensatory growth later on when lysine levels are adequate.In this case, pigs exhibiting compensatory growth have improved feed efficiency and increased amino acid requirements. 16Although this study was not purposefully designed to evaluate compensatory growth, the growth performance of pigs fed the 1-phase program during Phase 3 and 4 seems to indicate compensatory growth.It may be speculated that the lysine levels used in the present study were not sufficient to allow for an appropriate compensatory growth in late finishing that would overcome the poor performance in early grower stage.Alternatively, the reduction in lysine levels in early grower may have been too severe and/or too long.In conclusion, phase-feeding strategies provide advantages in growth performance and economics over feeding a single diet throughout the grow-finish phase.Moreover, simplification of feeding programs to two or three dietary phases with lysine levels slightly below the requirement estimates (98.5% of maximum growth rate) have negative implications on overall feed efficiency compared to a feeding program with four dietary phases.

Table 2 .
Composition of experimental diets (as-fed basis)1,2Lysine levels in experimental diets were achieved by manipulating the ratio of corn to soybean meal. 2

Table 4 .
Effect of phase-feeding strategy on growth performance, carcass characteristics, and economics of grow-finish pigs1,2,3