Reducing crude protein content with supplementation of synthetic
lysine and threonine in barley - rapeseed meal - pea diets

for growing pigs

Jarmo Valaja, Timo Alaviuhkola and Kaija Suomi

Valaja, J., Alaviuhkola, T. & Suomi, K. 1993. Reducing crude protein content with
supplementation of synthetic lysine and threonine in barley - rapeseed meal - pea
diets for growing pigs. Agric. Sci. Finl. 2: 117-123. (Agric. Res. Centre of Finland,
Swine Res. Sta., FIN-05840 Hyvinkää, Finland.)

This study was conducted to determine the possibility to use synthetic amino acids to
lower the nitrogen output from pig production. A performance experiment was carried
out with 120triplet-fed growingpigs whose dietary crude protein was reduced from 179
g/feed unit (FU= 0.7 kg starch equivalent) to 160, 140and 122 g/FU, respectively. The
diets were supplemented with synthetic lysine and threonine to keep the level of these
amino acids constant.

Dietary protein reduction did not affect the growth performance or feed conversion
ratio of the pigs, but it did linearly increase the portion of fat to lean in the carcass.
Significant linear effect was found in back fat (p<0.00l) and side fat thickness (pcO.Ol)
and in the proportion of lean in valuable cuts and in whole carcass (p<0.05).

However, the change in carcass composition was negligible down to a crude protein
level of 140 g/FU. It may, therefore, be concluded that the crude protein content of the
diet can be reduced by up to 20% by balancing the dietary protein with synthetic lysine
and threonine.

Keywords: pigs, growth rate, feed conversion ratio, carcass composition, nitrogen
excretion, crude protein, lysine, threonine

Introduction

Animal production causes serious environmental
problems in many European countries. The increas-
ing content of nitrogen in the soil, atmosphere and
fresh water, originating from manure, is a real prob-
lem in areas with high-density animal production
(Lenis 1989,Verstegen and Tammiga 1991).

Much effort has been focused on nutritional
means of reducing environmental pollution (Jong-
BLOED and Lenis 1992). In pig production, the
lowering ofnitrogen excretion is related to the pro-
tein content and amino acid balance of the diet,

since the oversupply of protein and the imbalanced
amino acids are excreted mostly in urine. A closer
balance of amino acids in the diet compared to the
requirement can be achieved, if feeding is based on
the requirements set by age and physiological state,
or if the availability and quality of the dietary pro-
tein are improved (Lenis 1989).

The availability ofeconomically viable synthetic
amino acids has made them an attractive alternative
in balancing the dietary amino acid composition of
pig feeds. A significant reduction in the crude pro-
tein content of cereal-based diets has been attained
with the supplementation of synthetic lysine alone,

117

Agric. Sei. Finl. 2 (1993)

https://www.c-info.fi/en/info/?token=HVzva3BGYjo98UzK.VlfEzR8gVsyD3rYrG0815w.EusRVNfcFa_Th6WCDQvU3eYlNXxGQQHQtYDWnzy55zUuXBa4XbzM3-6XA1qMCRN1uAssPhkkIHtWxktB97HWVYp7c4-I3LzjWJG4BbAW42KuJQGO96156R17KBhcWPe3ks47SsQu5MOSZpxZMNHr6udDWtNa10zeHZa8_fonVn3fBZBRO4yi2Wy3rlcVdWb_DTrUFIlMTeC22bRf19uJRh0GRAuv_kzlq7C5jxxiEj2XTZGOdd5FvqMxolJqUEzpxU_iiB4oku4_Ko6V_tIgfYDQHKWAg7H-Augs6BuKaGUz3DdMWg


without impairing the performance of the pigs
(Taylor et al. 1979, Easter and Baker 1980).
Furthermore, the reduction in dietary protein has
also depressed water consumption of the pigs,
which again leads to a smaller volume of excreted
urine (Pfeiffer and Henkel 1991).

This experiment was undertaken to make a com-
parison between the present protein feeding recom-
mendations for growing pigs in Finland based on
the digestible crude protein (Salo et al. 1990) and
balancing ofessential amino acid content of thediet
with synthetic amino acids with respect to the re-
quirements of growing pigs. The object of the ex-
periment was to determine the effects of the reduc-
tion in the crude protein content of the diet on the
performance and carcass composition of growing
pigs and on the nitrogen output from swine produc-
tion.

Material and methods

A total of 120Landrace and Yorkshire pigs, weigh-
ing 25.5 kg (standard error 0.19) on average, were
used in the performance trial. Three pigs of the
same sex and different litter origin were placed into
each pen and the pens were allotted at random to
one of four dietary treatments. The treatment
groups were balanced according to initial weight
and sex. Each diet was tested on 15 female and 15
castrated pigs.

The crude protein contents in the four diets were
179, 160, 140 and 122 g/FU, respectively. The

control diet, containing 179 g/FU crude protein,
consisted of barley, rapeseed meal (Brassica camp-
estris) and peas (var. Proco). The crude protein
content of the three experimental diets was reduced,
while the average lysine and threonine levels were
maintained at 9.0 and 6.2 g/FU with synthetic ly-
sine and threonine. Commercially produced lysine
hydrochloride and threonine (Eurolysine) were
used as supplementary amino acids. All diets con-
tained an adequate amount of minerals and vit-
amins to meet the nutritionalrequirements ofgrow-
ing pigs (Salo et al. 1990). The composition of the
four diets is presented in Table 1. The feed ingredi-
ents were analyzed by standard methods (AOAC

Table 1.Dietary ingredients (g/kg air-dry diet) and calculated
chemical composition of the diets.

Diet 12 3 4

Ingredients:
Barley 575 665 755 845
Rapeseedmeal 260 200 140 80
Peas 130 100 70 40
Mineral + vitamin mix. 2 35 35 35 35

Synthetic amino acids
L-lysine HCI, g/kg - 1.132.26 3.40
Threonine, g/kg - 0.511.02 1.55

Chemical composition:
Crude protein, g/kg 163 148 132 117
",g/FU' 179 160 140 122

Digestible crude protein, g/kg 128 117 105 93
",g/FU 141 126 111 97

Lysine, g/FU 9.09.0 9.09.0
Threonine," 6.46.3 6.15.9
Methionine+Cystine, " 6.76.1 5.54.9
Histidine, " 5.14.8 3.83.2
Leucine," 14.012.4 10.99.4
Isoleucine, " 7.96.9 6.05.1
Phenylalanine," 8.98.1 7.26.4
Arginine, " 11.710.0 8.46.9
Valine," 9.78.6 7.66.6
Feed unit (FU/kg DM) 1.041.06 1.071.09
ME,MJ/kg 14.30 14.41 14.5114.62

1 Feed unit (FU)= 0.7 kg starch equivalent.
2 Composition of mineral and vitamin mixture (per kg): Ca
200 g, P7sg. Mg 11.5 g, NaCl 103 g, Fe 3000 mg, Zn 2674
mg, Mn 1151 mg,Cu 1000 mg, Co38 mg, J 6 mg, Se 2.8 mg,
vitamin A 350 000IU, vitamin D 3 57 200IU, vitamin E 1200
mg, thiamine 57 mg, riboflavine 200 mg, pyridoxine 114mg,
pantothenic acid 430 mg, folic acid 114 mg, Bn-vitamin 570
pg and biotin 4000 pg.

1984), and their amino acid composition was deter-
mined by gas-liquid chromatography (GLC).

The pigs were housed in partially slatted pens
with concrete floors and had free access to water.
Feeds were given on a restricted scale in relation to
live weight twice daily (1.2-3.0 FU/day) according
to Finnish feeding standards (SALO et al. 1990).
Daily allowance was increased by 0.2 FU/animal/
week in the beginning of the experiment and by
0.1 FU/animal/week after the ninth experimental
week. The pigs were slaughtered at an average
weight of 105 kg.

The carcass weight was recorded 24 h after
slaughter. The left half of the cold carcass of each

118

Agric. Sei. Finl. 2 (1993)



pig was cut into valuable cuts (ham, fore-end,
shoulder and loin), and the cuts were dissected to
determine lean (including bones) and fat (including
skin). The proportion of lean and fat was calculated
from the ham, valuable cuts and whole carcass. The
area of the longissimus dorsi muscle was deter-
mined posterior from the last rib with a planimeter.
The thickness of back fat was calculated as a mean
of five measurements (shoulder, middle and ham
(mean of three measurements)), and the thickness
of side fat was determined from the end of longis-
simus dorsi.

Nitrogen excretion was calculated as the differ-
ence between nitrogen supply from the diet and
total nitrogen retention during the experiment. The
quantity of nitrogen retained in thebody during the
experiment was calculated as the difference be-
tween the nitrogen content of the pig at the end of
the experiment and the estimated nitrogen content
of the pig in the beginning of the experiment. The
nitrogen retained in the carcass was estimated from
the dissection results as a sum of the nitrogen in the
carcass lean and bones (including head). The pro-
portion of blood, intestines and offals was estim-
ated as the difference between slaughter loss pro-
portion and gut fill. The content of nitrogen in
carcass lean and bones and the initial nitrogen con-
tent of the pigs were adapted from the dissection
and the chemical analysis results of40 pigs slaugh-
tered at regular intervals between 20 and 110 kg
live weight (Alaviuhkola et al., unpublished).
The proportion of gut fill and the content of nitro-
gen in the blood, intestines and offals were estim-
ated from the results ofWhittemore and Elsley
(1976).

The data were analyzed by the GLM procedure
of SAS (1990). The hierarchic analysis of variance
was performed as outlinedby Gill(1989) using the
model: yijkl= p + di + sj + (ds)ij + pk(ds)ij + eyk,
where d, s and p are diet, sex and pen effects,
respectively, ds is the effect of diet*sex, and eyk is
the error term. The effect of pen within diet*sex
interaction (pk(ds)y) was used as an error term for
testing the diet and sex effects. Feed consumption
was registered on pen basis and the pen effect was,
therefore, excluded from the model in statistical
testing. Slaughter weight was used as a covariate in

the testing of carcass trait measurements. The de-
grees of freedom for the diet effect were further
partitioned into single degrees offreedom totest the
linear, quadratic and cubic trends of the crude pro-
tein level.

Results

One gilt on diet 4 was excluded from the trial for a
reason unrelated to the treatment. Otherwise the
pigs completed the experiment successfully, and
refusals of the diets were negligible. The overall
results of the experiment are given in Table 2. The
quadratic and cubic trends of the crude protein
content and diet*sex interaction were non-signific-
ant and are therefore omitted from Table 2.

Performance

The growth performance of the pigs was good over
the entire experimental period, averaging 880
g/day. The daily gain (DG) and feed conversion
ratio (FCR) of the pigs were unaffected by the
reduction in the dietary crude protein level. Total
(p<0.05) and daily (p<0.01) feed consumption
(measured as feed units) increased linearly with the
reduction in the crude protein content. No signific-
ant differences between sexes were found in the
performance of the pigs.

Carcass composition

There was a significant difference in carcass weight
(p<0.05) between the four groups, which also pro-
duced a difference in the corrected final weight
(p<0.05). The carcass composition of the pigs
changed from lean to fat when the crude protein
content in the diet decreased, while a significant
linear increase was found in back fat (p<0.001) and
side fat (p<0.05) thickness. The lean content in
valuable cuts and in the carcass also decreased
linearly (p<0.05). However, no signicant differ-
ences were found in the area of the longissimus
dorsi muscle between the treatments.

119

Agric. Sei. Fint. 2 (1993)



Table 2. Performance and carcass composition of the pigs (LS means of the treatments are presented).

Treatment 12 3 4 Sex Significance
SEM Females Castrated SEM treatm. Sex

males linear
Crude protein, g/FU 179 160 140 122

No. of animals 30 30 30 29 59 60
Initial weight, kg 25.425.5 25.525.5 0.3225.7 25.20.22 NS NS
Final weight, kg 104.8104.7 105.1105.6 0.53104.9 105.20.38 NS NS
Final weight (corr.)„kg' 103.9104.6 105.4106.4 0.81105.3 104.90.57 * NS
Daily gain, g 871 881 890 883 11.1 881 881 7.84 NS NS
Daysinexp. 90.490.4 90.292.1 1.3690.7 90.90.96 NS NS
Feed consumption,
FU/animal 209.8209.8 211.8221.6 3.70212.5 214.02.59 * NS
FU/day/animal 2.322.32 2.352.41 0.0222.34 2.350.015 ** NS
FCR, kg DMAg gain 2.572.51 2.472.49 0.0352.50 2.520.024 o NS

", FUAggain 2.672.65 2.652.74 0.0372.67 2.690.026 NS NS
", MJ ME/kg gain 41.241.4 41.142.0 0.5741.3 41.50.40 NS NS

Carcass weight, kg 76.977.4 78.078.7 0.6077.9 77.60.73 * NS
Loss at slaughter, % 26.325.9 25.925.9 0.2025.8 26.20.14 NS NS
Back fat thickness, mm 24.425.0 26.327.3 0.5125.3 26.20.37 *** o
Side fat thickness, mm 16.517.7 17.918.9 0.5516.5 19.00.39 ** ***

Area of/, dorsi,cm2 43.443.0 42.743.3 0.5944.7 41.40.42 NS ***

Lean in ham, % 81.881.6 81.080.7 0.4381.7 80.80.30 o *

Lean in valuable cuts, % 80.680.4 79.879.2 0.4080.6 79.40.28 * **

Carcass lean, % 53.953.7 53.052.9 0.3753.9 52.90.26 * **

Significance: NS= non-significant, o=p<o. lo, *= p<0.05, **=p<o.ol, ***=p<o.ool. SEM=standard error of means.
FCR= feed conversion ratio.

1 Final weight corrected with 26.0 % loss at slaughter.

Significant differences between sexes were
found in side fat thickness (p<o.ool )and in the area
of the longissimus dorsi muscle (p<0.001) as well
as in the proportion of lean in ham (p<0.05), valu-
able cuts (p<0.01) and whole carcass (p<0.01). In
all these measurements, gilts were found to be su-
perior to castrated males.

Nitrogen excretion

The total quantity of nitrogen retained in the body
for treatments 1,2,3and 4 was 1.65,1.65,1.64and
1.64 kg/pig, respectively (Table 3). Correspond-
ingly, the quantity ofnitrogen ingested per pig was
6.01, 5.37,4.74 and 4.33 kg, and nitrogen excreted
(ingested - retained) was 4.36, 3.72, 3.10 and 2.69
kg, respectively.

Table 3. Calculated nitrogen balance of the pigs.

12 3 4
179 160 140 122

Treatment
Crude protein, g/FU

6.015.37 4.744.33
1.651.65 1.641.64

Nitrogen ingested, kg/pig
Nitrogen retained, kg/pig
Nitrogen excreted, kg/pig 4.363.72 3.102.69
Difference in nitrogen excretion
compared to control group

0.63 1.24 1.67
14.7 28.4 38.3

kg/pig
%

Discussion

The results of this study clearly confirmed that it
was possible to reduce nitrogen excretion in swine
production by applying a suitable feeding strategy.

120

Agric. Sei. Finl. 2 (1993)



In our experiment, lysine and threonine were
chosen as the supplementary amino acids because
they are the two most limiting amino acids in bar-
ley-based diets (FULLER et al. 1979a, 1979b). Simi-
lar results have been also obtained in other perform-
ance trials(Taylor et al. 1979,Easter and Baker
1980) and balance trials (Gatel and Grosjean

1992, NÄSI 1985) with the supplementation of
lysine only.Easter and Baker (1980) reduced the
dietary crude protein content of a com-soybean
meal diet by 10% without observing any negative
effects on the performance of the pigs. Further-
more, Taylor et al. (1979) showed that the crude
protein content ofa barley-soybean meal diet could
be lowered from 17.6to 14.5% , but at lower levels
the performance of the pigs started to deteriorate.
Gatel and Grosjean (1992) reported that a 7.5%
decrease in nitrogen intake resulted in a 15 to 20%
decrease in nitrogen excretion in a balance trial
with growing pigs. In another trial by the same
authors, in which soybean meal was substituted by
peas and supplemented with synthetic lysine,
threonine, methionine and tryptophan, even a 35%
decrease in nitrogen excretion could be achieved by
a 15% decrease in nitrogen intake. NÄSI (1985)
found that there was not any further increase in
nitrogen retention after lysine supplementation
when methionine was added to a low-protein diet of
growing pigs.

A progressive reduction in crude protein with the
supplementation of only one amino acid leads to a
lack of other essential amino acids or non-essential
protein. In our experiment, the deterioration in car-
cass trait mesurements indicated that amino acids
other than lysine or threonineor non-essential pro-
tein became limiting factors for lean growth. His-
tidine is regarded as the third limiting amino acid in
barley (Fuller et al. 1979a), but its content in diet
4 was found to be on the level of the minimum
recommendation ofARC (1981), 3 g/kg vs 2.8 - 4.0
g/kg. The content of sulphur-containing amino
acids may also have been a limiting factor for lean
growth in treatment 4 when the balance between
essential amino acids was compared to ideal protein
determined by Wang and Fuller (1989) (54 vs
63). The ratio of threonineto lysine in diet four was
lower than that reported by WANG and Fuller

(1989) (66 vs 72), but it was above the ratio given
by ARC (1981) (60). On the other hand the calcula-
tions ofARC (1981) and the present study are based
on a total amino acid basis, whereas WANG and
Fuller (1989) used ileal digestible amino acids in
their determination.The ratio between essential and
non-essential amino acids in all diets was above the
minimum ratio (45:55) of WANG and FULLER
(1989).

Taylor et al. (1979) reported, that the deteriora-
tion of carcass quality started at a higher level of
dietary protein compared to the deterioration in the
performance of the pigs. The fact that the highest
content of lean was found in thecontrol group could
also be theresult ofusing excess dietary protein for
energy, since crude protein is a poor energy source,
with the net energy accounting for only about 50 %

of the gross energy (Just 1982).
The diets in our experiment were designed on a

total lysine basis. Flowever, there is a marked dif-
ference between the reported digestibilities of syn-
thetic lysine (Leibholz et al. 1986) and the lysine
in peas (Buraczewska et al. 1989) and rapeseed
meal (Sauer and Thacker 1986), which resulted
in different amounts of digestible lysine in the ex-
perimental diets. Our performance results indicate
that the difference in the utilizationof synthetic and
protein-bound amino acids is much smaller than
expected, as also confirmed in the recent studies of
Jorgensen and Fernandez (1988), Susenbeth et
al. (1991) and Matre and Home (1991).

Our calculations concerning the reduction in ni-
trogen excretion showed differences of about 0.63,
1.24and 1.67 kg (14.7,28.4 and 38.3%) in nitrogen
excretion per pig between the control group and
treatments 2, 3 and 4, respectively (Table 3). The
results are in agreement with the calculations of
Lenis (1989), who found that a reduction of 2
percentage units in the crude protein content of
diets of growing pigs resulted in a reduction in
nitrogen excretion of about 25%. Jongbloed and
LENIS (1992) have also calculated that nitrogen
output could be lowered by 1 kg per pig by restrict-
ing the protein level of the diet and by adding
synthetic lysine and methionine.

Gilts and castrated males showed similar growth
performance in our experiment, although castrated

121

Agric. Sei. Finl. 2 (1993)



males deposited more fat compared to gilts. A
higher rate of fat deposition in castrated males is
usually accompanied by reduced growth (Yen et al.
1986). However, results similar to ours have been
obtained in earlier studies (Taylor et al. 1979,
Alaviuhkola et al. 1992). It is possible that the
amount of lysine in our trial diets was not sufficient
for the gilts to show their full performance.

In conclusion, the results show that it is possible

to reduce the crude protein content of the diets of
growing-finishing pigs by up to 20% with the addi-
tion of synthetic lysine and threonine, resulting in a
reduction of about 30% in nitrogen excretion. How-
ever, the practical implementation of the feeding
strategy depends on the price difference between
the protein and energy feedstuffs and on the avail-
ability of synthetic amino acids at competitive
prices.

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Manuscript received March 1993

Jarmo Valaja
Timo Alaviuhkola
Kaija Suomi
Agricultural Research Centre of Finland
Swine Research Station
FIN-05840 Hyvinkää,Finland

Jarmo Valaja
Present adress:
Department of Animal Science
P.O. Box 28
FIN-00014 University of Helsinki, Finland

SELOSTUS

Lihasikojen rehun raakavalkuaisen täydentäminen puhtailla aminohapoilla

Jarmo Valaja, Timo Alaviuhkola ja Kaija Suomi

Maatalouden tutkimuskeskus

Lihasikojen kasvatuskokeessa tutkittiin dieetin raakavalkuais-
pitoisuuden alentamisen ja synteettisen lysiini- ja treoniinitäy-
dennyksen vaikutuksia tuotantotuloksiin ja teuraslaatuun. Yh-
teensä 120sikaa, joistapuolet imisiä japuolet leikkejä, jaettiin
neljään yhtä suureen ryhmään. Siat pidettiin kolmen eläimen
karsinoissa, joissa sukupuolet olivat erillään. Rajoitettu iän-
mukainen ruokintanormi oli 1,2-3,0ry/sika/pv. Sikojen keski-
määräinen alkupaino oli 25,5 kg ja loppupaino teuraaksi lähe-
tettäessä 105,0 kg.

Vertailuryhmän rehuseos koostui ohrasta, rypsirouheesta,
herneestä sekä kivennäis- ja vitamiiniseoksesta ja sisälsi raa-
kavalkuaista 179 g/ry (sulavaa raakavalkuaista (SRV) 141
g/ry). Kolmen koeryhmän dieeteissä vähennettiin rypsirou-
heen ja herneen osuutta lineaarisesti, mutta rehuseosten lysii-
ni- ja treoniinitasot pidettiin samana synteettisen lysiini- ja
treoniinilisäyksen avulla(lysiiniä 9,0 g/ry ja treoniinia 5,9-6,4
g/ry). Dieettien raakavalkuaispitoisuus oli 160, 140 ja 122
g/ry (SRV 126, 11 1 ja97 g/ry).

Raakavalkuaispitoisuuden alentamisella ei ollut vaikutusta
sikojen päiväkasvuun tai rehuhyötysuhteeseen, kun dieetin
lysiini-ja treoniinimäärät pidettiin samana. Valkuaispitoisuu-
den alentaminen heikensi kuitenkin suoraviivaisesti sikojen
teuraslaatua. Selkä- ja kylkisilavan paksuus kasvoi ja lihan
osuus koko ruhossa sekä sen arvokkaissa osissa väheni. Käy-
tännössä erot olivat kuitenkin varsin pieniä valkuaistasoon
140 g/ry asti. Keikkojen tai unisien välillä ei havaittu eroja
päiväkasvussa tai rehuhyötysuhteessa, muna kikkojen teuras-
laatu oli selvästi heikompi kuin imisien.

Kokeen tulosten perusteella rehun raakavalkuaispitoisuutta
voidaan alentaa ainakin 20 %, kun dieetin aminohappokoos-
tumusta samalla täydennetään sopivasti synteettisen lysiinin
ja treoniinin avulla. Samalla vähennetään myös virtsan ja
sonnan mukana vapautuvan typen määrää. Menetelmän käyt-
tö on kuitenkin käytännössä riippuvainen eri rehukomponent-
tien hintasuhteista.

123

Agric. Sei. Fin!. 2 (1993)