Ideal Digestible Lysine Level for Early- And Late-finishing Swine

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J. D. Hahn, R. R. Biehl and D. H. BakerIdeal digestible lysine level for early- and late-finishing swine

1995, 73:773-784.J ANIM SCI

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IdealDigestible LysineLevelorEarly- andLate-Finishing Swine]Joseph D. Hahn2,Robert R. Biehl, and David H. BakesDepartment of Animal Sciences and Division of Nutritional Sciences,University of Illinois, Urbana 61801

ABSTRACT Two hundred ixteen crossbred (P ICline 26 x Camborough 15) pigs were used in hreetrials to determineoptimaldigestible ysine levelsduring early (E F =50 to 95 kg) and late (LF=90 t o110 kg) finishing periods. Pigs were self-fed in sexgroups of two in all trials. The assay diets for EF andLF periods were 11 and 10% CP corn-soybean mealdiets,espectively,upplementedwithhreonine,methionine, tryptophan, valine, and isoleucine. Corn-soybean meal positive-control diets were included ineach trial (14.5% CP for EF and 13.5% CP for LF).This die tary CP regimen was shown to give the sameperformance and carcassquality as a 17% CP corn-soybean meal diet fed during both EF andLF. Plateauportions of the lysine esponse urves esulted in

performance levels that were equal to o r greater thanthose achieved with pigs fed the 14.5/13.5% CPpositive-control diets.Early-finishing pigs responded(P < . 0 5 ) to graded doses of digestible lysine ( .41 to.71%) for daily weight gain, gain:feed, longissimusmuscle area, 10th-rib fat depth, lean gain, andlasmaurea N. Digestible lysine requirement estimates basedon average plateau points were 58% for E F barrowsand .64% for EF gilts. Late-finishing pigs responded( P


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774 HAHN ET AL.Table 1. Percentage composition (as-fed basis) of basal diets for Trials 1 and 2and of the corn-soybean meal diets used in Trials 1 to 3

Corn-soybeanmeal diets,Trial s 1, 2, Trial 1 Trial 2

Inaedientnd 3a basalietasalietCornstarchCornDehulledsoybeanmealSoybean oilL-Threonine, feed gradeDL-Methionine, feed gradeL-Tryptophan, feed gradeL-IsoleucineL-ValineDicalcium phosphateLimestoneTracemineral mixbVitamin mixcB M D ~Analyzed composition

Crudeprotein, %Total lysine, %

-VarVar3.00-----1.50.75.35.l 0.03

VarVar

to 100.0082.4011.582.50

.20

.l0

.05

.03

.031.50

.75

.35

. l0

.0311.3

.51

to 100.0085.219.002.25

.20

. l 0

.05

.03

.031.50.75.35. l0.03

10.0.44

and soybean meal were varied to obtain 14.5 and 13.5% CP diets that were used as positivecontrol diets for EF an d LF, respectively, for the lysine requirement trials (Tria ls 1 and 2). In Trial 3,these positive control diets (14.5% CP o 90 kg, 13.5% CP from 90t o 107 kg ) were compared to a 17% CPdiet fed during both EF and LF.Lysine levels in these diets were .89, .74, and .67% for the 17, 14.5, and13.5% CP die ts, respectively.bTrace mineral mix provided t he following (p e r kilogram of diet): Se, 30 mg; I, .35 mg; Cu , 8 mg; Mn,20 mg; Fe, 90 mg; Zn, 100 mg; NaCl, 2.73 g.Witamin mix provided the following (per kilogram of diet): vitamin A, 3,300 units ; vitamin D3, 330units; vitamin E, 44 units; vitamin K, 2.2 mg; vitamin B12, .02 mg; riboflavin, 4.4 mg; d-pantothenic acid,12.1 mg; niacin,16.5 mg; choline chloride, 165 mg.dBMD antibiotic provided 33 mg bacit racinkg of diet.

L26 males and Camborough 15 females were used forall experiments.Animal Housing. Pigs were housed tw o pigslpen ina mechanically ventilatedinisher uilding. ens

measured 1.8 m x 2.7 m and provided a usable floorarea of 2.2 m2/pig. Flooring was a combination of solidconcrete and slats (approximately 50:50). Water wasprovided fo r ad ibitum ntake by nipplewaterers.Temperature in the finishing building ranged from 18to 26C duringhehreerials.Experimental Diets. Diet composition is presentedin Table 1. Cornand soybean meal were stored in bulkto ensure consistency within and among trials. Bothingredients were analyzed (Table 2 ) for CP (AOAC,1990 ) nd amino acid content (Spackman t l.,1958) following 22-h acid hydrolysis. Analysis forcystine and methioninewas done on amples pre-oxidized with performic acid (Moore, 1963). Trypto-phan wasssayed followingiOH hydrolysis(Degussa, Allendale, NJ). Amino acid hydrolysateswere analyzed using a Beckman model 126 amino acidautoanalyzer using Beckman System Gold chromatog-raphy software (Beckman nstruments, Palo Alto,CA). The 11 and 10% CP basal diets were formulatedto meet o r exceed all NRC (1988) nut rie nt require-ments, excluding lysine, for pigs between 50 and 110kg. They containedallessentialamino acids at or

above their ideal ratio to lysine for the finishing pig(BakerndChung, 1992; Baker,993). Lysineadditions t o the EF and LF basal diets were made atthe expense of cornstarch. The digestible lysine levelobtained by the treatment diet containing the highestlevel of crystalline lysine-HC1 inclusion (.71% lysinefor EF trial; .65% lysine for LF trial) was set as thebase level (100). Digestible levels of all otheressentialamino acids were based on their ratio tolysine (e.g., threonine was added to the EF basal diett o attain a digestible threonine level that was 70% of.71% lysine,or .50%). Thismethod of amino acidsupplementationensured tha t both the EF and LFbasal diets would be singly deficient in lysine. Thus,both EF and LF basal diets were supplemented withthreonine,methionine,ryptophan, isoleucine, andvaline.Apparentmino acid digestibilityalues weredetermined by feeding the 11 and 10% CP basa l diets(Table 1 ) o seven finishing pigs fitted with a simpleT cannula at the terminal ileum (Easte r and Tanks-ley, 1973). Collection and processing of digesta wereas described by Sauertl.1991).Apparentdigestibility of crystalline amino acids was assumed obe 100%. Although the ideal pat tern usedherein sbased on true digestibilityvalues,use of apparentdigestibility is adequate for diets based on corn and

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LYSINE FOR INISH ING PIGSTable 2. Amino acid composition (as-fed basis) of corn, soybeanmeal, and basal diets used in Trials 1 and 2a

Ingredientbrial 1 basalietrial 2 basalietAmino acid Corn SBM Total Digestible' Total DigestibleC

775

LysineMethionineMet +CysdThreonineTryptophanIsoleucineValineCrude Drotein

%.22 2.82 .51.l 8 .6933 .37 1.43 .57.30.93 .67.07 ,423 . l6.29 2.20 .52.40 2.32 .63

6.866.211.3

.41 .44 .35

.283126 .455443

.536350

. l2l5l1

.414737

.475844 - 10.0 -aAmino acid evels repre sent mean values of four amino acid hydrolysates. Duplicate hydrolysateswere performed on two separate samplings of the corn and soybean meal. Analysis for methionine andcystine was performed on samples pre-oxidized with performic acid.bSBM = dehulled soybean meal , solvent.CApparent amino cid digestibility esti mates were obtained by feeding the basal dietso seven finishingdMet + Cys repr esents sum of methionine and cystine levels.pigs fitted with a simple T cannula at the termina l ileum.

soybean meal,becausesimilar results are expected.Differences that do result would lead t o an underesti-mation of digestibility by the apparent digestibilitymethod, and a onsequent overfortification of thebasal diet.

In Trial3 the 14.5% CP positive-control EF diet waschanged at a body weight of 90 kg to 13.5% CP for LF,and his was compared to a 17% CP corn-soybeanmeal diet fed during both EF and LF (Table ) .Crudeprotein levels in these diets were achieved by varyingthe corn:soybean meal atio.Basedonamino acidanalysis of the corn and soybean meal, the 17, 14.5,and 13.5% CP diets contained total lysine concentra-tions of .89, .74, and .67%, respectively.ExperimentalProtocols

TriaZ 1. A randomized complete-block design with asplit-plot arrangement(sex was themain plot anddiethe ubplot) was sed.Ninety six pigs (48barrows, 48 gilts) with an average initial weight of52.0 kg were allotted t o blocks based on sex, ancestry,and weight. Individual pigs within blocks wererandomly assigned t o one of six dietary treatments.The heaviest two blocks within a sex were placed inthe pens corresponding to replicate one of that sex.Theext two heaviest blocks were assignedoreplicate two of the appropriate sex. This process wascontinued until ll replicates ad been assigned.Location within the finisher building was randomizedfor treatment within the six pens associated within abarrow or gilt replicate. Pigs were fasted 12 h beforeinitial and final weights were taken at the termina-tion of the growth portion of the trial. The weight gainand feed efficiency data were summarized at the timewhen the pen with the heaviestverageweightreached the targeted slaughter weight of 90 k '2 kg.

Treatments included thebasaldiet or thebasalsupplemented with feed-grade lysine.HC1 o provide 0,.075, .150, .225, or .300% supplemental ysine.Thedigestible lysine levels produced were .41, .48, 36 , .63,and .71%. A 14.5% CP corn-soybean mealietcontaining .74% total ysine was fed as a positivecontrol.

Pigs were fed the experimentaliets for a39-d period, after which growth and feedefficiencydata were summarized.The pigs then remained ontheir respective diets until they reached average penslaughter weights of 90 k 2 kg. Blood samples fromindividual pigs were collected from the cranial venacava region into ithium heparinized yringes ju stbefore the 12-h fast on d 39 of the tria l was begun.Blood samples were centrifuged (2,000 x g for 10min).Equal volume aliquots of plasma from eachsample were pooled by pen and analyzed for plasmaurea nitrogen ( N ) concentration. When meanpenweights reached 90 k 2 kg, both pigs in that pen wereslaughtered.Pigs were killed at a commercial meatprocessing facility and hot carcass weight wasrecorded. After chilling, the carcasses were split andthen cutbetween the10thand11th ib to allowmeasurement of longissimus muscle area nd fatdepth.Lean ainwas alculated singhe ameassumptions for percentage of muscling in the init ialcarcass nd the ame equation for calculation ofpercentage of muscling in the final arcass as reportedby Cromwell etal. 1993). Themusclingequationused by Cromwell et al. (1993) was a modification ofthe NPPC (19 76) quation. Although a newer equa-tion is available (NPPC, 19911, the old equation wasused to allow direct comparisons between our data andthose of Cromwell et al. (1 99 3) . Use of the newerequation resulted in an average lean gain increase of7% for our pigs.by guest on January 30, 2012jas.fass.orgDownloaded from


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776 HAHNTria2 2. A randomized complete-block design with a

split-plot arrangement (sex was he main plot anddiet the subplot) was again used. Ninety-six pigs (48barrows, 48 g ilts) with an average initial weight of90.6 kg were allotted t o blocks based on sex, ancestry,and weight.ndividual pigs within blocks wererandomly assigned t o one of six dietary treatments.Assignment o replicates and pens was the same asth at described for Trial 1. Pigs were fasted 12 hbeforeinitial and final weighings. Pigs were fed the basaldiet o r theasal supplementedwith feed-gradelysine.HC1 to provide 0, .075, . E O , .225, or .300%supplementalysine.he digestible lysine levelsproduced were .35, .43, 50, .58, and .65% lysine.A13.5% CP corn-soybean mealdietwasused as apositive control. It contained .67% totalysine.

Pigs were fed the experimentaliets for an18-d period, after which performance data weresummarized. The pigs then remained on their respec-tive diets until mean pen weights reached 110* 2 kg.Blood samples from individual pigs were collected andanalyzed as described for Trial 1.Pigs were killed andcarcasses measured as described for Trial 1, and leangainwas alculatedusing the ame quation forpercentage of muscling in he final carcass as thatused for Trial 1, but percentage of muscling in theinitial carcass was based on the mean valuesobtainedfor the control pigs of corresponding gender at th etermination of Trial 1.Trial 3. A randomized complete-block design with asplit-plot arrangement(sex was themain plot anddiet the subplot) was also used for this trial. Twenty-four pigs (12 barrows,12 gilts)withanaverageinitial weight of 57.0 kg were assigned to blocks basedon sex, litte r, and weight. The litte rmate pairs thatformed th e blocks were randomly assigned o repli-catesand placed in pens as described for the twoprevious trials. Pigs were fed a 16% CP corn-soybeanmeal diet prior to allotment. They were fasted 12 hbefore the initial and final weighings. Early-finishingdiets were fed from 57 to 90 kg, and LF diets were fedfrom 90 to 107 kg. Diet changes (14.5 -+ 13.5% CP)were made when mean pen weights reached 0 k 2 kg;the 17% CP diet,however, was fed during bothEF andLF. Pigs were fed the experimental diets until meanpenweightseached 107 k 3 kg.StatisticalAnalysis

All data were analyzed using the GLM proceduresof SAS (1985), using pen as the experimental unit.Experiments were analyzed byANOVA (Table3)appropriate for randomized complete-block designswith a split-plot arrangementSteel nd Torrie,1980). Pooled SEM values reported were based on thereplicate x dieterror erm(Table 3 ) andare onlyappropriate for comparison of dietaryreatmentmeans. The error term used o test for sex effects wasreplicate in sex. This resulted ina lower sensitivity for

ET AL.Table 3. Analysis of variance for Trials 1 , 2, and 3a

SourceDegrees of freedom

Trials 1 and 2 Trial 3Total 47 11Replicate 7 5Sex 1 1

Replicate in sexb 6 4Diet 5 1Error (replicate x diet) 35 5Sex x diet 5 1Replicate in sex x diet 30 4

aAppropriate ANOVA for andomized omplete-block designswith a split-plot arrangement (Steel and Torrie, 1980).Sex is themain plot and diet is the subplot.bReplicate in sex was used as the error erm or sex effects.

measuringsex effects. In Trials 1 and 2, single dforthogonalcontrasts were used t o test inearandquadraticesponses to lysine upplementation fortreatments 1 to 5 . Whereppropriate,esponsecriteria were fitted to a rectilinearbroken-linemodel, andhiswas usedo estimate a lysinerequirement. Separate regression analyses were con-ducted for barrows andgilts,and responsecriteriawere regressed on digestible lysine concentration. Thebreak-points for the different performance and carcassmeasurements were determined using a model involv-ing one linear spline and a plateau (Robbins, 1986).

ResultsTrial 1. A sex difference (P . l o ) from those achieved in pigs fedthe 14.5% CP positive-control diet.



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LYSINE FOR FINISHING PIGS 77

w l n w

w m c

w m c

w m co r l m o c d n j cN



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778 HAHN ET AL.Table 5. Digestible lysine requirements of finishing pigsa

Breakpoint Digestible Totalperformance lysine, % lysine', B

Measurem ent Barrow Gilt Barrowiltarrowilt50 to 90 kg (Tria l 1)Daily gain, g 1,079 972 5 0 .65 .59 .76Gain:feed, g k g 3 13 34656 .64 .66 .75Lean gain, gld 352 345 .57 .64 .67 .75Fat depthc, 10th rib,mm 22.3 16.2 .62 .67 .73 .76Longissimus area, cm2 33.1 35.3 .60 .6571 .79Plasma urea Ne, mgldL 10.7 9.2 .60 .6171 .72Pooled average - - .58 .64687590 to 110 kg (Tr ial 2)

Daily gain, g 1,068 979 .50 .5059 .59Gain:feed, g k g 283 301 .50 .52 .59 .61Lean gain, gld 342 366 5 0 .535961Plasma urea Ne , mg1dL 12.1 8. 2 .46 .5454 .64Pooled average - - .49 .52 .5861

Calcu lated using he GLM procedure of SAS (19 85) and the broken-line model described by Robbins ( 19 86 ).aRequirement obtained by r egressi ng the mea n treatme nt values for each paramet er on the digestible lysine concentr ation of the diet.bDigestible ysine concentration converted to otal lysine assum ing 85% lysine digestibility in a corn-soybean meal diet.

Gain:feed ratio was negatively correlated (P


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LYSINE FOR FINISHINGIGS 77

r l 3 m

t-do



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780 HAHN ET AL.

Leangain,g ld

360

340

320

300

280

Early Finisher

T

T

.. A

260 I I I I I I.354555 .75Digestible lysine, %

360

340

320

300

280

BeakpointBa =352 g I d ; 57% ysineG i = 3 4 5 g l d ; . M % l y s i n e

260.354555Digestible lysine, Yo

Ba =10.69 rng I dL ; .60 Yo lysineGi = 9.21 m g Id L ; .61% ysine

9 . 0 t- A

8.0 I I I I I.354555Digestible ysine, %

Figure 1. Selected broken-line plots from Trial 1. Plots are gain:feed ratio, lean gain, and plasma urea Nconcentration as a function of digestible ysine concentration. Responses to increasing dietary concentrations ofdigestible lysine are shown for both barrows ( 0 ) nd gilts [ A ) .Data points represent means k SE of four replicatepens of two pigs perpen.



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LYSINE FOR FINISHINGIG S 781320

300

280

260

c Late Finish er- -- .-__-._.__._._.._.__._._.__._...____L i 4 Gi

T\l Ba-Breakpoints

Ba =283 gI g ; .50 O h lysineGi =301 g kg : .52 % ysine

Gain:feed,9 1 g

I JL . I U .30 . 4 0 .50 -60 .70

Digestible lysine,%

Late Finish er80 - Late Finish er .____._._. .__ _ _ _ . _ . .h Gi360 -340 - l T Ba

BreakpointsBa = 342 g I d ; 50 % ysineGi =366 g I d ; .53 % ysine

I I I

.30 .40 .50 .60 .70Digestible lysine,O h

T T

Leangain,g l d

12.5 -% T 0 T.Y BaPlasma 11.5mg I L -.rea N,

-' ---*.a- '.0.5..

'. _ BreakwintsS. *-_. B a = 1 1 . 5 8 m g l d L ; . 4 6 % l y s i n e

9.5 - ""l---...,.-a Gi = 7.23 mg I dL ;5 4 % ysine8.5 - '.*-=. .-.----_ _ _ _ _.___ _ _ . _ _ __ GiP7 .S I 1 I I I.30 .40 .50 .60 .70

Digestible lysine,%

Figure 2. Selected broken-line plots from Trial 2. Plots are gain:feed ratio, lean gain, and plasma urea Nconcentration as a function of digestible lysine concentration. Responses to increasing dietary concentrations ofdigestible lysine are shown for both barrows (0)nd gilts ( A ) .Data points represent means k SE of four replicatepens of two pigs per en.



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782 HAHN ET AL .Table 7. Performance and carcass composition of finishing pigs fed two protein regimensduring early (EF) and late finishing (LF) periods (Trial 3)a

Barrows GiltsDiet: 1 2 1 2CP level, %b: 14.5113.5 17.0 14.5113.57.0 Pooled

Measurement SEMCDaily gain, g 1,043 1,033 1,003 9982.1Dailyfeed,g 3,437 3,322 3,036 3,143 81.9Gain:feed, &g 304 312 332 318.1Daily lean gain, gd 337 336 365 356 3.2Longissimus area, cm2 37.4 37.5 37.9 38.4 1.13Fat depth (10th rib), mme 26.8 26.5 24.0 22.5 .40

bThe diet conta ining 14.5% CP fed was fed from 57 to 90 kg (EF) andwas followed by the di et containing 13.5% CP from 90 t o 107 kgaMeans within sex represent three replicate pens of two pigs; average initial weight was 57.0 kg and average ending eight was 107.3 kg.(LF) . Thedietconta ining 17.0% CP was fed from 57 to107 kg.CPooledSEM was based on the error termused t o tes t the effect of diet (subplot); theseSEM values are not appropria te or evaluation ofsex (main plot ) effects.dCalculated by dividing th e difference of the estimated lean in final carca ss an d the lean in the initial carcassdivided by the number ofdays on trial. Estima tes of the initial composition are values reported or 50-kg pigs of this genotype by Hahn (1994 ); percentag e f musclingin the final carcass was estimated as described by Cromwell et al. (1993), using the percentage of muscling equation from NPPC (1976).eMeasured according to established procedures for 10th-rib fat measurem ent (NPPC, 1991).

digestible lysine on a concentrationbasis, and from11.78 to 23.19gld of digestible ysine on an ntakebasis, Although a significant portion of the variationin stimates can be attributed t o sex, ublishedestimates of the lysine requirement for finishing pigsare variable within sex, and it is difficult to separateresponse t o lysine, t o protein level, o r t o energydensity.

In a broad-based study of the protein and lysinerequirement of finishing pigs by Cromwell et al.(1 99 3) , gain, efficiency of gain, and lean growth ratereached a plateau in barrows at 13% CP (.60% totallysine), but lysine and protein concentrations in thisstudy were achieved by changing the rat io of corn:soybean meal in he diet. In gilts, Cromwell et al.(1 993 ) found in two of three trials that performancewas near a plateau at 17.2% CP (.go% to tal lysine).When our determined requirements fo r the EF period(Table 6 ) ar e converted t o a totalysineasis(assuming aysine igestibility of 85%, in corn-soybeanmeal diets ), otal lysine requirementesti-mates of .68% or barrows and .75% for gilts result.Compared withhe stimates of Cromwell et al.(19 93 ), our requirement estimates fo r the EF periodarehigher han heirs fo r barrows but lower thantheirs fo r gilts. Yen et al. (1986b ) reported responsesof growing pigs to a source of dietary ideal protein.Based on total lysine, the equirement fo r barrowswas .72% lysine (18 .6 gld) in a diet containing 11.6%CP, and the requirement for gilts was .85% (21.2 gld)in a diet containing 13.4% CP. The estimated barrowrequirement of Yen et al. (198613) is highe r than thatdeterminedherein fo r the EF barrow (Table 6 ) o rthat reported by Cromwell et al. (19931,but heestimatedgilt equirement allsbetweenourvaluedetermined fo r th eEF gilt and hat reported byCromwell et l.1993).

Both EF ndLFgilts required igher ietaryconcentrations of lysine than EF and LF barrows tomaximize growth performance and carcass eanness.Similar results have been reported previously (Bakeret al., 1967; Hale and Southwell, 1967; Bereskin et al. ,1976; Watkinsetal., 1977; Christian etal., 1980;Henry et al., 1992). Concentration requirements canvary over the inishing period simply due to therelative partitioning (1ean:lipid ratio) of the weightgain. Differences in appetite and part itioning of gaincreate a situation in which the gilt is inherently moreefficient at depositing protein than the barrow whenboth are growing at a ratenear heir maximumpotential. Tullis(1981) eported that gilts had higherlean deposition rates than barrows across the entireweight range of 50 to 90 kg, and tha t the efficiency ofN utilization was grea ter fo r gilts than for barrows.The higher efficiency of dietary N utilization in gilts isconsistent with the resu lts of our experiments. Giltsutilized dietary lysine more efficiently th an barrows,as demonstrated by their ability in the EF period t oproduce the same amount of lean gain per day as thebarrows on a lower intake of lysine. In the LF period,gilts produced 7% more lean gain per day on a lowerintake of lysine. The greater efficiency of utilization ofdietary lysine by the gilt is consistent with the dat aofCromwell et al. (19 93 if their reported lean deposi-tion rates reported are regressed on lysine intake(intake calculated by multiplyingeportedysineconcentration by reported feed intake).

The total lysine intake required is a function of therate of lean deposition, the efficiency of lean deposi-tion, and the appetiteo r feed intake potential of a pig.In our EF trial,barrows consumed approximately 20%more feed and grewapproximately 11%faster hangilts.Thedailyweightgainadvantage of finishingbarrows over gilts has been shown previously (Baker



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LYSINE FOR FINISHING PIGS 783et al., 1967; Bereskin et al., 1976; Christianet al.,1980; Cromwell et al., 1993). Because total weightgain per day was significantly (P < .05) higher nbarrows than in gilts, the barrows actually depositedthe same quant ity f lean tissue per day s the gilts inthe EFperiod, but the percentage of gain deposited aslean was reduced, and thus the overall efficiency ofgain was reduced as well. In the LF period, the giltwas able to deposit more total lean per day than thebarrow, and the gilt required a lower lysine intake toaccomplish th at lean deposition. A higher daily intakerequirement for lysine by the barrow was observed inboth the EF and LF periods as a result of the lowerutilization of dietary lysine by the barrow relative tothe gilt.The ability of barrows in our study to produce ratesof lean gain equal to those of gilts is in contrast o theresults of Tullis (1981) and Yen et al. (1986b). Thebarrows inheirtudies, however, did not growappreciably fast er than the gilts. Total daily weightgains of barrows were only 104% of that obtained ingilts in the study y Tullis (19811, and theywere only94% of those obtained by gilts in the studies y Yen etal .1986b). Appetite or growth-rate otential ofbarrows relative t o gilts seems t o vary with genotype,and it may explain why our EF barrows could reachthe same ratesof lean gain deposition as the EF gilts.Unt il he maximum rate of protein deposition isachieved, increases in protein intake result in linearincreases in protein deposition rate as appetitepotential increases (Whittemore, 1987; Campbell andTaverner, 1988). Gilts can achieve higher maximumrates of lean gain deposition th an barrows, as shownby the rate s of lean gain for our pigs in theLF period.During EF, however, the tremendous appetite poten-tial of the barrows allowed them t o deposit lean attheir maximum rate. The EF gilts may be limited inleangainpotential by theirappetite for a argerportion of the trial period relative to the barrows. Thiswould result in themaximal rate of lean deposition forthe gilts being achieved for a smaller portion of th e EFtrial period.

Pigs fed our low-protein experimentaldiets,withlysine at or above its determinedrequirement,per-formed as well as those fed theigher-proteinpositive-control diets. This raises the question of theadequacy of the 14.5%CP positive-control diet for EFand he 13.5% CP positive-control diet for LF. Thedata from Trial 3 (Tab le 7) clearly demonstrated tha ta 14.5% CP (corn-soybean meal diet) fed from 50 t o90 kg followed y 13.5% C P from 90 t o 110kgproduced the samegrowth performance and carcassmerit, including lean gain, as th at obtained by feedinga 17% CP corn-soybean meal diet from 50 t o 110 kg.

Pigs in our trials were confined two per pen underwhat might be termed ideal environmentalconditions.This probably contributed to he excellent perfor-mance levels achieved. Thus, our feed intake levelswere higher th an those generally expected for either

EF or LF pigs. Would the lysine requirements behigher fo r pigs in a commercial setting with higherstockingdensities?The evidence seems to indicatethat he combined stress factors of crowding anddisease level th at may decrease voluntary feed intakeare not likely t o increase the lysine equirementexpressed as a percentage of the diet. In fact, thelysine requirement expressed as grams/day is ikely t odecrease. Chapple (19 93 ) reported tha t pigs wereunable t o reach he same genetic potential for leangrowth when confined in groups of five t o eightcompared to hepotential of similar pigs pennedindividually. Also, we have compared our 14.5/13.5%CP regimen for EFLF pigs to a 17% CP corn-soybeanmeal iet fed continuously during othinishingperiods under conditions of nine pigdpen Hahn,1994). Pigs were of the ame genotype as thoseherein. No differences were found in growth perfor-mance or carcass merit between the two dietaryprotein regimens, even though the pigs housed nine/pen (.65m2/pig) consumed approximately 7% less feedthan those housed two/pen (2.2m2/pig)under hesame conditions as those used for the two trialsreported erein.

ImplicationsIf low-protein corn-soybean meal diets are formu-

lated to ideal levels of digestible lysine, hreonine,tryptophan,methionine (+ cystine),aline,ndisoleucine, excellent performance can be achieved. Thedetermined ysine equirements for early inishingbarrows and gilts are higher than those suggested bytheNational Research Council; for late-finishingbarrows andgilts, however, the NationalResearchCouncil requirement suggestions are similar t o thosefound herein. Gilts require a higher level of digestiblelysine than barrows, and the difference between sexesis greater during early finishing (50 t o 90 kg) thanduringate finishing (9 0 to 110 kg).

LiteratureCitedAnonymous. 1993. Nutrition for PIC pigs: Feeding for lean meat

potential. PIC Technical Update (1.3-93). Pig mprovementCompany, Franklin, KY.AOAC. 1990. Offlcial Methods of Analysis (1 5t h Ed.). Association ofOfficial Analytical Chemists, Arlington, VA.

Baker, D. H. 1986. Problems and pitfalls inanimalexperimentsdesigned tostablishietaryequirement s for essentialnutrients. J. Nutr. 116:2339.

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Ideal Digestible Lysine Level for Early- And Late-finishing Swine