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Swiss Federal Station for Animal Production, Posieux, 1725 Switzerland
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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9-desaturase activity that was induced by CLA
rather than an altered rate of de novo synthesis.
KEY WORDS: • piglets • conjugated linoleic acids • adipose tissue • lipogenesis
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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, Chin et al. 1994
, West et al. 1998
) and to act as a repartitioning agent in
growing-finishing pigs (Dugan et al. 1997
,
Ostrowska et al. 1999
). Dietary CLA infused into the
abomasum of dairy cows has been reported to increase CLA content of
milk fat, to alter milk fatty acid composition and to markedly depress
the total content and yield of milk fat (Chouinard et al. 1999
). Furthermore, CLA infusion dramatically reduced palmitic,
linoleic and arachidonic acids and increased stearic acid content of
cow’s milk (Loor and Herbein 1998
). Results of a recent
study identified t10,c12–18:2 as the CLA isomer
responsible for the inhibition of milk fat synthesis by reducing de
novo lipid synthesis (Baumgard et al. 2000
).
Neonatal growth in pigs depends primarily on milk produced by the
sow as the sole source of energy during early development. Piglets are
born with extremely little body fat (Le Dividich et al. 1994
) and low reserves of stored glycogen (Boyd et al. 1978
); thus, sufficient energy uptake after birth is important.
Suckling newborn piglets are unable to synthesize fatty acids from
carbohydrate (Le Dividich et al. 1994
); deposition of
body fat depends in large part on the amount of fat intake (Le Dividich et al. 1997
). The most promising strategy to improve
neonatal piglet growth rate is to increase the fat content of the
maternal milk (Averette et al. 1999
). Both the yield and
lipid composition of the colostral and mature milk can be manipulated
by the amount and origin of dietary fat provided to pregnant and
lactating sows (Fritsche et al. 1993
). In agreement with
the latter studies, we reported that compared with a control treatment
(linoleic acid), dietary CLA in the sow lactation diet significantly
increased the level of saturated fatty acids and decreased that of
monounsaturated fatty acids in the milk lipids (Bee 2000
). In addition, dietary CLA isomers
(c9,t11; t10,c12;
t9,t11/t10,t12;
c9,c11) were excreted in the milk and, therefore,
were available to the suckling pigs. The question arises whether the
modified fatty acid composition and the amount of CLA in the milk
lipids affect growth performance and tissue composition of neonatal
pigs. In view of the results reported by Chin et al. (1994)
, indicating the possibility that CLA may act as a growth
factor on development and growth of rats, the objective of this study
was to establish, by feeding CLA to sows during pregnancy and lactation
and further offering CLA in a starter diet after weaning, to what
extent growth and fat metabolism of the piglets were influenced.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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The 40 piglets used in this study were progeny of multiparous Swiss
Large White sows that were fed from the day of mating, during pregnancy
and lactation either a diet supplemented with 2 g of oil enriched
with linoleic acid per 100 g of diet (LA; n
= 4) or a diet supplemented with 2 g of oil enriched with a
commercially available CLA per 100 g of diet (CLA;
n = 6; SELIN-CLA, Grünau Jllertissen
GmbH, Jllertissen, Germany). The linoleic acid–enriched oil,
derived from sunflower oil, served as source material to produce CLA
(Grünau Jllertissen GmbH). Details regarding the housing,
nutrition, management and experimental conditions of sows are described
elsewhere (Bee 2000
).
Two females and two castrates from each of 10 litters were selected on
the basis of the mean body weight of the litter at d 35 of lactation.
After 35 d of rearing, piglets from two sows fed LA and piglets
from three sows fed CLA were randomly assigned to each of two starter
diets. The piglets were given for 35 d free access to a starter
diet shown in Table 1
that was supplemented with CLA or LA (2 g/100 g diet). The same lots of
LA- and CLA-containing oils were used for the sow diet and the
starter diet. The experimental groups were denoted in the text and
tables as follows: treatment LL (n = 8) and LC
(n = 8), pigs reared on sows fed the LA diet and then
fed the LA or CLA starter diet, respectively; and treatment CL
(n = 12) and CC (n = 12), pigs reared
on sows fed the CLA diet and then fed the LA or CLA starter diet,
respectively. Body weight of each pig was recorded at birth, weaning
and d 35 of the starter period. From weaning until slaughter, the four
selected piglets from each individual litter were housed in a separate
pen under normal husbandry conditions. Feed consumption was recorded
for each pen and average total feed intake and average feed efficiency
ratio were calculated. Grouping piglets from different litters in a
single pen was avoided to prevent losses of piglets due to piglet scour
or edema in the first 10 d after birth. Furthermore, it was
imperative to exclude medical treatments with antibiotics during the
postweaning period because that would have questioned or confounded
possible growth-promoting effects of CLA. All procedures involving
animals were approved by the Swiss Federal Committee for Animal Care
and Use.
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The diets were withdrawn 12 h before the pigs were brought to the abattoir of the research station, where they were electrically stunned and exsanguinated. Internal organs were removed and the warm carcasses were weighed. The semitendinosus muscle was removed from the right side of each carcass and the weight, girth and length was recorded. The loin eye area was determined at the level of the 13th rib of the longissimus dorsi muscle. Furthermore back fat and omental fat were collected from each pig and stored at -20°C until fatty acid profiles were determined. Samples of longissimus dorsi muscle were lyophilized, homogenized and stored at -20°C for further analysis.
Sample analysis.
Adipose tissue and longissimus dorsi muscle were analyzed for total
lipid content by the method of Winter (1963)
and fatty
acid methyl esters (FAME) were prepared as reported earlier (Bee 2000
). CLA and FAME were determined by gas chromatography (HP
5860 A GC, Urdorf, Switzerland). Methyl tridecanoate (91560, Fluka,
Buchs, Switzerland) was used as internal standard to quantify the FAME.
CLA standards (Matreya,, Pleasant Gap, PA) were used to identify each
CLA peak. A beef-pig blend reference standard (CRM 163: Commission
of the European Communities, Community Bureau of Reference, Brussels,
Belgium) was used to validate the measurements. The following CLA
isomers were determined: cis9,trans11
(c9,t11)-,
trans10,cis12
(t10,c12)-,
cis9,cis11
(c9,c11)- and
cis10,cis12
(c10,c12)-18:2. The
trans9,trans11
(t9,t11)- and
trans10,trans12
(t10,t12)-18:2 could not be separated and
are reported as the sum of both isomers.
At the abattoir, weighted quantities of back fat and omental fat were
homogenized in an ice-cooled 0.25 mol/L sucrose buffer (in 0.1
mol/L phosphate buffer, pH 7.4). The samples were centrifuged twice at
15,000 x g for 10 min and the supernatant
recentrifuged at 30,000 x g for 40 min in the same
buffer. The supernatants were stored at -70°C to assess lipogenic
enzyme activities using standard photometric methods. Samples were
analyzed in duplicate for glucose-6-phosphate dehydrogenase (G6PDH, EC
1.1.1.49), malic enzyme (ME, EC 1.1.1.40) and fatty acid synthase (FAS,
EC 2.3.1.85) using the methods of Löhr and Waller (1974)
, Hsu and Lardy (1969)
and Roncari (1981)
, respectively. NADPH formation (G6PDH, ME) or oxidation
(FAS) was measured at 37°C by absorbance at 340 nm. A commercial
protein dye-binding assay kit, using bovine 
-globulin as a
standard, was used to measure the soluble protein concentration in the
supernatant fraction (Bio-Rad Protein Assay, Bio-Rad, Glattbrugg,
Switzerland). The enzyme activities were expressed as µmol NADPH
produced or oxidized · min-1 · mg-1
protein.
Statistical analysis.
Data analyses were performed with the PROC GLM procedure of SAS (1998)
. The experimental model was a 2 x 2 x 2
factorial randomized ANOVA. Least-square values were obtained
assuming fixed models that included the effects of sex, rearing (R) and
starter (S) period. Growth performance data in the rearing period were
analyzed as a 2 x 2 randomized ANOVA with R and sex as main
factors. The individual pig values were considered as the experimental
unit of all response variables. Significant sex and R x S effects
were indexed in the tables. No significant R x sex, S x sex
and R x S x sex interactions were found. Differences of
P < 0.05 were considered significant.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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). The CLA starter diets (LC, CC) were lower in palmitic
(16:0), stearic (18:0) and linoleic acids and slightly higher in oleic
acid compared with the respective control (LL, CL). None of the CLA
isomers were detected in the diets supplemented with the
linoleic-enriched oil.
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Body weight at birth and weaning were not affected by the diet fed to
the dams during gestation and lactation (Table 3
). However, irrespective of the dietary fat supplied in the starter
period, piglets reared on sows fed CLA had greater total feed intake
(P = 0.02), higher daily weight gain (P
< 0.01), and higher final body (P < 0.01) and
warm carcass weights (P < 0.01) than piglets reared on
sows fed LA. Feed efficiency did not differ between groups
(P = 0.42).
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Loin eye area and girth and weight of semitendinosus muscle of piglets
reared on dams fed CLA were significantly larger and heavier than those
of piglets suckling sows fed LA (Table 4
). However, compared with the respective controls, the loin eye area was
smaller (P = 0.01) and the semitendinosus muscle was
shorter, if weaned piglets were fed the CLA supplemented starter diets
(LC and CC).
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The effect of dietary CLA on the fatty acid composition was similar for
back fat (Table 5
) and omental fat (Table 6
). Supplementation with CLA in the preweaning period markedly increased
the levels of lauric (12:0), stearic, and total saturated fatty acids
(SFA) (P < 0.01 for each), whereas those of
palmitoleic acid [16:1(n-7)], eicosenoic acid [20:1(n-9)] and total
monounsaturated fatty acids (MUFA) were decreased in both tissues
(P < 0.05 for each); oleic acid was increased and
heptadecanoic [17:0] and linoleic acids were decreased only in the
back fat (P < 0.05). Feeding of the CLA-enriched
starter diet had even more pronounced effects on these same fatty acids
and also on myristic (14:0) and palmitic acids. However, palmitoleic
acid in back fat and omental fat and oleic acid and MUFA levels in
omental fat were not affected by CLA in the starter diet. The presence
of CLA in the starter diet caused linoleic, eicosadienoic
[20:2(n-6)], arachidonic [20:4(n-6)] and linolenic acids
[18:3(n-3)] and total polyunsaturated fatty acid (PUFA)
concentrations to be significantly decreased in both fat tissues. The
ratios of palmitoleic to palmitic acid [16:1(n-7)/16:0] and oleic to
stearic acid [18:1(n-9)/18:0] were markedly decreased by dietary CLA
ingested during both the lactation and starter periods. In contrast to
the fatty acid profile, total lipid content in both back fat and
omental fat was unaffected by diet.
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and 6
). By contrast, the piglets fed CLA during
the rearing and/or starter periods incorporated CLA isomers, dependent
on the supply. The most abundant was c9,t11 and
in decreasing order t10,c12 > t9,t11/t10,t12 > c9,c11 > c10,c12–18:2. The lowest detectable levels of
isomers were found in the CL and the highest in the CC group. The
c10,c12–18:2 was present only at trace levels in
the CL group. The CLA contents of the back fat and omental fat were
similar and do not indicate a preferential incorporation into either
tissue. Due to significantly elevated levels of lauric, myristic, palmitic and palmitoleic acids (0.14 vs. 0.13; 2.07 vs. 1.87; 28.89 vs. 26.96; 2.50 vs. 2.20 g/100 g total fatty acids, respectively), barrows showed a more saturated fatty acid pattern than gilts in the omental fat, whereas that of the back fat did not differ between sexes. The higher concentrations were compensated mainly by slightly but not significantly lower depositions of oleic and linoleic acids (P = 0.41 and P = 0.17), respectively. Additionally, barrows had significantly lower levels of c9,t11; t10,c12 and t9,t11/t10,t12 (1.11 vs. 1.31; 1.04 vs. 1.26; 0.54 vs. 0.64 g/100 g total fatty acids). No significant interactions occurred between experimental treatments and sex for any of the fatty acids.
Fatty acid profile of lipids in longissimus dorsi muscle.
The total lipid content of the loin muscle was significantly affected
by the preweaning treatment (Table 7
), with lower levels found in the CL and CC groups. However, the fatty
acid composition was affected in a similar way as previously presented
for the adipose tissue. An exception was the level of palmitoleic and
linolenic acids, which were elevated in the piglets fed the
CLA-enriched starter diet (LC, CC). Total PUFA content was not
influenced by dietary treatment. In contrast to the fat pads,
c10,c12–18:2 could not be detected,
t10,c12 was the most abundant CLA isomer in the
longissimus muscle instead of c9,t11 in the fat
tissues, and the overall CLA level was markedly lower.
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Lipogenic enzyme activities;
Irrespective of the dietary treatment, the activity of key lipogenic
enzymes was higher in the omental fat than in the back fat (Table 8
). The presence of CLA in the starter diet, but not in the rearing
period, markedly increased the activity of G6PDH and ME in both
tissues. The effect of the CLA supplement was more pronounced when
piglets were weaned from sows receiving linoleic acid than from sows
receiving CLA (R x S interaction P < 0.05). In
contrast, FAS activity was unaltered by the fat supplemented to the
diet.
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|
DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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), feed efficiency was similar for
both groups (Dugan et al. 1997
). In addition, neonatal
growth was unaffected by the nutrition of the dams. We can only
speculate on the reasons for these surprising results. Previously, we
observed that compared with sows fed a control diet, sows fed a
CLA-enriched diet tended to have lower fat content in the mature
milk (unpublished observations). However, on the basis of the growth
performance of those litters, which depends mainly on the sow’s milk
production (King et al. 1998
), we concluded that milk
yield might not have been decreased by the supplementation of CLA to
the dams. The observation that piglets reared by sows gain less weight
than those reared artificially provides evidence that sow-reared
neonates have unrealized growth potential (King et al. 1998
). The two major reasons for the slower growth rate are the
availability and composition of the milk. One can question whether the
supply of milk CLA during lactation might have impeded the maximal
possible growth rate, which then resulted in compensatory growth in the
postweaning period when feed was freely accessible. In addition to
enhanced growth performance, pigs reared on sows supplemented with CLA
also had improved morphometric muscle measurements for semitendinosus
(+17% heavier, P = 0.02; +9% larger, P
< 0.01; +5% longer, P = 0.09) and longissimus
dorsi (+14% larger loin eye, P = 0.02), resulting in
greater warm carcass weights that were influenced mainly by the rearing
period rather than by the postweaning diet. Further investigation is
required to determine to what extent these effects were due to
hypertrophy of muscle fibers.
CLA was reported to reduce the catabolic responses induced by immune
stimulation without adversely affecting immune function (Miller et al. 1994
). These responses are mediated by cytokines and
regulated by prostaglandin E2 synthesis.
Recently, CLA was found to lower the level of prostaglandin
E2 in both serum (Sugano et al. 1997
) and bone organ cultures (Li and Watkins 1998
) and reduce cytokine production (Sugano et al. 1997
). In addition to affecting the immune response, cytokines
induce catabolic processes in skeletal muscle (Hotamisligil and Spiegelman 1994
). Therefore, reducing the immune response may
have provided more available energy for anabolic processes.
Additionally, the concept of CLA as a nutrient with
growth-promoting effects might be supported by the observation that
CLA had insulin-sensitizing effects in Zucker rats
(Houseknecht et al. 1998
). Dietary CLA could have acted
similarly to fats rich in 20/22-carbon fatty acids (e.g., fish oil) by
enhancing peroxisomal fatty acid oxidation due to induced acyl Co-A
oxidase expression in skeletal muscle, which in turn is accompanied by
enhanced expression of glucose transporter-4 gene and improved glucose
uptake in skeletal muscle. Therefore, anabolic effects on muscles
reported in this study for piglets reared on sows fed CLA could be due
to reduced immune stimulation in the early stage of development of the
neonate and/or elevated fuel supply to the muscle resulting from
improved glucose utilization.
Previous studies have shown that only trace amounts of free fatty acids
cross the swine placental tissues during gestation; therefore, their
contribution to fetal energy supply or lipid storage appears limited
(Thulin et al. 1989
). From a number of observations
reviewed by Leskanich and Noble (1999)
, it appears that
de novo lipogenesis at birth, the principal mechanism of fatty acid
accretion, is low. This deficit in body lipid content is largely
rectified through the piglet’s access to a rich lipid source in the
form of maternal milk. In view of the fact that in our housing system
and under the present experimental conditions, the suckling pigs did
not have access to the sow’s diet, the presence of CLA isomers
(c9,t11; t10,c12; and
t9,t11/t10,t12) in the fat
of CL pigs clearly shows that CLA in the milk lipids were absorbed by
the suckling piglets and incorporated in the early stage of fat
accretion. In the mature milk of CLA-fed sows, the
c10,c12–18:2 isomer was not detected and the
amount of c9,c11–18:2 was low [0.5 g/100 g
total fatty acids; (Bee 2000
)], which explains the
absence of these isomers in the tissue lipids of the CL group. Although
both the rearing and starter period lasted for 35 d each, compared
with the milk (CL), the CLA intake from the starter diet (LC) was
higher and resulted in marked differences in CLA deposition between the
groups. In the tissue lipids of piglets fed CLA during the rearing and
starter periods, the highest amounts of CLA isomers were incorporated
and were on average the sum of those found in the CL and LC group. For
the piglets of CL and CC treatments and in agreement with recent pig
data (Kramer et al. 1998
), the relative absorption of
all the isomers seemed to be similar because there was little
difference in general between the distribution of CLA isomers in the
commercial CLA preparation fed to pigs and the adipose tissue. If CLA
was supplied only by the milk (c9,t11, 38 g;
c9,c11, 11 g; t10,c12,
34 g; c10,c12, 1 g;
t9,t11/t10,t12: 17 g/100 g
of total milk CLA), relatively more c9,t11–18:2
(43%) and less c9,c11–18:2 (5%) was deposited,
which might be due to differences in absorption rates and therefore
availability of the milk lipids rather then selectivity in deposition.
However, a certain tissue selectivity for the main isomers is suggested
by the pattern of CLA enrichment because compared with the adipose
tissue, t10,c12 CLA was the most abundant isomer
in the muscle. These findings corroborate previous results in rats
(Li and Watkins 1998
) and were independent of CLA supply
by the milk or diet. The tissue fatty acid composition is a dynamic
system constantly receiving, oxidizing and incorporating dietary fatty
acids. The metabolic turnover in adipose tissue is lower than in other
tissues (Otten et al. 1993
); therefore, differences in
CLA incorporation might also be due to differences in turnover rates of
certain isomers or selective discrimination.
Irrespective of the starter diet, intramuscular fat content of piglets
reared on sows fed CLA were lower than those of the control group. We
assume that the lower fat content was associated mainly with reduced
triacylglycerols rather than differences in phospholipid deposition
because the latter seems to remain constant after postnatal development
(Lebret et al. 1999
). The present data are in contrast
with a study showing increased fat deposition in the longissimus
thoracis in growing-finishing pigs (Dugan et al. 1999
), but corroborate the reported CLA effects on body
composition (Ostrowska et al. 1999
). The question arises
whether differences in the t10,c12 CLA level, the
most abundant isomer found in the muscle, were responsible for or
triggered the differences in fat deposition (Baumgard et al. 2000
, Park et al. 1999
). However, this does not
explain why the intramuscular fat content of the LC group was similar
to that of the CC group.
The fatty acid composition of the pig tissues was significantly modified by the dietary lipids. CLA consumption in the rearing period increased the concentration of stearic acid and total SFA, but decreased that of palmitoleic and oleic acids and total MUFA. CLA feeding in the postweaning period further enhanced the differences. In addition, linoleic, linolenic and arachidonic acids and total PUFA were markedly decreased. The linoleic acid–enriched diet could only partly overcome the effect of the maternal milk CLA on the tissue fatty acid composition (CL), which might be due to the fact that already deposited CLA isomers affected fat metabolic pathways.
G6PDH and ME are the main enzymes involved in supplying NADPH for the
reductive biosynthesis of fatty acids (Mourot et al. 1995
), but they also contribute to metabolic pathways other
than lipogenesis. Both fat tissues of pigs receiving CLA in the starter
diet had greater G6PDH and ME activities than those in pigs receiving
the LA starter diet. The G6PDH activity was higher than ME in both
tissues and seemed to be the main producer of NADPH. This observation
agrees with comparative studies in newborns (Le Dividich et al. 1994
) and growing pigs (Mourot et al. 1995
).
Furthermore, the inclusion of CLA in the starter diet had a greater
effect on enzyme activities in the back fat of pigs reared on sows fed
LA in the diet than in pigs reared on sows fed CLA, suggesting that the
presence of CLA isomers during rearing had already altered fat
metabolism before pigs received the starter diet. Perhaps the effects
of dietary CLA on activities of ME and G6PDH are indirect rather than
direct. Increasing concentrations of glucose have been reported to
result in the progressive induction of ME (Mariash and Oppenheimer 1984
) and G6PDH (Boll et al. 1996
).
Assuming that CLA has insulin-sensitizing effects and improves
glucose utilization by the adipocytes, the effects found on ME and
G6PDH activities could in fact be related to elevated availability of
glucose induced by the dietary CLA rather than a direct effect of CLA
on the enzymes.
The activity of FAS was markedly higher in the omental fat than the
back fat, and could explain the differences in the fat content of the
two tissues. However, the fatty acid composition was somewhat
contradictory to the enzyme activity. Dietary CLA supply markedly
increased tissue SFA, fatty acids that derive primarily from the diet
and de novo synthesis, but had no effect on FAS activity. The lower
ratio of palmitoleic to palmitic and oleic to stearic acid in all
tissues of the LC, CL and CC experimental groups compared with the LL
group could indicate a down-regulation of 9-desaturase activity,
which was proposed by other authors (Li and Watkins 1998
, Pariza et al. 2000
) and could explain the
high amount of SFA in the tissues. The low tissue level of arachidonic
acid of animals fed CLA further suggested that other desaturases
(6-, 5-desaturase) might be affected by dietary CLA as was
observed in research with rodents (Belury and Kempa-Steczko 1997
).
In conclusion, piglets reared on sows fed CLA during pregnancy and
lactation grew faster in the postweaning period, irrespective of the
starter diet. Furthermore, they deposited higher amounts of SFA, which
was compensated mainly by a lower content of MUFA in the adipose and
muscle tissue. When weaned piglets were fed a CLA-enriched starter
diet, the effects on fatty acid composition were even more pronounced.
The elevated SFA deposition due to dietary CLA was related to an
inhibition of the 9-desaturase activity and probably other
desaturases, rather than elevated de novo synthesis rate.
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ACKNOWLEDGMENTS |
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FOOTNOTES |
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Manuscript received April 19, 2000. Initial review completed May 31, 2000. Revision accepted August 7, 2000.
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