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Nutritional and physiological role of medium-chain triglycerides and medium-chain fatty acids in piglets

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Medium-chain fatty acids (MCFAs) are found at higher levels in milk lipids of many animal species and in the oil fraction of several plants, including coconuts, palm kernels and certain Cuphea species. Medium-chain triglycerides (MCTs) and fatty acids are efficiently absorbed and metabolized and are therefore used for piglet nutrition. They may provide instant energy and also have physiological benefits beyond their energetic value contributing to several findings of improved performance in piglet-feeding trials. MCTs are effectively hydrolyzed by gastric and pancreatic lipases in the newborn and suckling young, allowing rapid provision of energy for both enterocytes and intermediary hepatic metabolism. MCFAs affect the composition of the intestinal microbiota and have inhibitory effects on bacterial concentrations in the digesta, mainly on Salmonella and coliforms. However, most studies have been performed in vitro up to now and in vivo data in pigs are still scarce. Effects on the gut-associated and general immune function have been described in several animal species, but they have been less studied in pigs. The addition of up to 8% of a non-esterified MCFA mixture in feed has been described, but due to the sensory properties this can have a negative impact on feed intake. This may be overcome by using MCTs, allowing dietary inclusion rates up to 15%. Feeding sows with diets containing 15% MCTs resulted in a lower mortality of newborns and better development, particularly of underweight piglets. In conclusion, MCFAs and MCTs offer advantages for the improvement of energy supply and performance of piglets and may stabilize the intestinal microbiota, expanding the spectrum of feed additives supporting piglet health in the post-weaning period.
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Nutritional and physiological role of
medium-chain triglycerides and medium-chain
fatty acids in piglets
J. Zentek
1
*, S. Buchheit-Renko
1
, F. Ferrara
1
, W. Vahjen
1
, A. G. Van Kessel
2
and R. Pieper
1
1
Department of Veterinary Medicine, Institute of Animal Nutrition, Freie Universita
¨t Berlin,
Bru
¨mmerstrasse 34, 14195 Berlin, Germany,
2
Department for Animal and Poultry Science, College of Agriculture and Bioresources,
University of Saskatchewan, 51 Campus Drive, Saskatoon, SK S7N 5A8, Canada
Received 11 November 2010; Accepted 24 March 2011
Abstract
Medium-chain fatty acids (MCFAs) are found at higher levels in milk lipids of many animal
species and in the oil fraction of several plants, including coconuts, palm kernels and certain
Cuphea species. Medium-chain triglycerides (MCTs) and fatty acids are efficiently absorbed and
metabolized and are therefore used for piglet nutrition. They may provide instant energy and
also have physiological benefits beyond their energetic value contributing to several findings of
improved performance in piglet-feeding trials. MCTs are effectively hydrolyzed by gastric and
pancreatic lipases in the newborn and suckling young, allowing rapid provision of energy for
both enterocytes and intermediary hepatic metabolism. MCFAs affect the composition of the
intestinal microbiota and have inhibitory effects on bacterial concentrations in the digesta,
mainly on Salmonella and coliforms. However, most studies have been performed in vitro up
to now and in vivo data in pigs are still scarce. Effects on the gut-associated and general
immune function have been described in several animal species, but they have been less
studied in pigs. The addition of up to 8% of a non-esterified MCFA mixture in feed has been
described, but due to the sensory properties this can have a negative impact on feed intake.
This may be overcome by using MCTs, allowing dietary inclusion rates up to 15%. Feeding
sows with diets containing 15% MCTs resulted in a lower mortality of newborns and better
development, particularly of underweight piglets. In conclusion, MCFAs and MCTs offer
advantages for the improvement of energy supply and performance of piglets and may stabilize
the intestinal microbiota, expanding the spectrum of feed additives supporting piglet health in
the post-weaning period.
Keywords: piglets, medium-chain fatty acids, medium-chain triglycerides, metabolism,
antibacterial effects, immune system
Introduction
Composition of the dietary-derived lipids, specifically
carbon chain length, distribution of fatty acids in triacyl-
glycerols and degree of saturation of fat, affect lipid
metabolism in piglets (Gu and Li, 2003). Medium-chain
fatty acids (MCFAs) are saturated 6–12 carbon fatty acids,
which occur naturally as medium-chain triglycerides
(MCTs) in milk fat and various feed materials, especially
coconut, palm oils and Cuphea seed oils (Graham, 1989;
Dierick et al., 2003; Marten et al., 2006). During palm
or coconut oil refining, MCT oils are produced as by-
products from hydrolyzed triglycerides by re-esterification
of glycerol and fatty acid distillates enriched by fractional
distillation or the free fatty acids are used without further
*Corresponding author. E-mail: zentek.juergen@vetmed.fu-berlin.de
*
cCambridge University Press 2011 Animal Health Research Reviews 12(1); 83–93
ISSN 1466-2523 doi:10.1017/S1466252311000089
processing (Nandi et al., 2005). Both MCFA and MCTs
have specific nutritional and metabolic effects, including
rapid digestion, passive absorption and obligatory oxida-
tion, making them particularly interesting for the nutrition
of young animals (Odle, 1997). Antimicrobial effects of
MCTs and MCFAs have been described as well as a pro-
tective effect on the intestinal microarchitecture based
on studies in pigs (Dierick et al., 2003). MCFAs have
also been suggested to have immune-modulating effects
(Wang et al., 2006), but evidence from the pig is lacking
(Buchheit, 2009).
The weaner piglet is an ideal target for exploiting
the nutritional and physiological effects of MCFA and
MCTs in the post-weaning period. In piglets, the changes
associated with the critical post-weaning phase often
result in reduced feed intake, causing energy deficiency,
modifications in the intestinal morphology, reduced
absorptive and barrier functions, impaired immune re-
activity and altered composition of the intestinal micro-
biota (Pluske et al., 1997; Konstantinov and Smidt, 2006;
Lalle
`set al., 2007). The gradual decrease in maternal
immunoglobulins from the sow’s colostrum (Rooke and
Bland, 2002), the not yet fully developed active immune
system of piglets (Scharek and Tedin, 2007; Butler et al.,
2009) and the continuous contact with new microbes
from the environment are factors associated with a high
risk of gastrointestinal disease, which can cause diarrheal
disorders and considerable piglet losses (Lalles et al.,
2007).
The administration of MCFAs appears to provide a
promising approach to reduce complications associated
with the post-weaning phase in piglets. The modes of
action, however, are not fully understood. This review
article is focused on the mechanisms of action and the
nutritional and physiological efficacy of MCFAs that are of
particular interest in piglet nutrition and may serve as an
alternative, non-antibiotic approach to improve perfor-
mance and health.
Chemical structure and occurrence of MCFAs
MCFAs are saturated and unbranched monocarboxylic
acids. This group consists of caproic acid (C6:0, hexanoic
acid), caprylic acid (C8:0, octanoic acid) and capric acid
(C10:0, decanoic acid). Lauric acid (dodecanoic acid) with
12 carbon atoms is also often classed with the group of
MCFAs (Bach and Babayan, 1982). All naturally occurring
fatty acids are composed of C2-units (acetyl-CoA) and
thereby have an even number of carbon atoms.
Due to a shorter hydrocarbon chain length compared
to long-chain fatty acids, MCFAs have a low melting point
and a comparatively high solubility in water. At a neutral
pH, the MCFAs are mostly dissociated (ionized) (Bach
and Babayan, 1982). The standard chemical properties of
caproic, caprylic, capric and lauric acid are summarized in
Table 1.
For young animals, the milk of their mothers is a crucial
source of MCFAs, occurring in varying concentrations
depending on the species. High concentrations of MCFAs
are found in the milk of the mouse, rat, rabbit, goat, horse
and elephant. Cow and sheep milk and human breast
milk contain only small amounts of MCFAs. Merely trace
amounts can be detected in the milk of the sow, the camel
and the guinea pig (Witter and Rook, 1970; Decuypere
and Dierick, 2003). It is not fully understood as to why
MCFA concentrations differ among species; however,
species-specific discrepancies in the activities of tissue-
specific thioesterases appear to be responsible for the
varying efficacies in synthesis (Libertini and Smith, 1978;
Rudolph et al., 2007). MCFAs occur naturally as parts of
triglycerides in various vegetable fats/oils, particularly,
coconut and palm. Typically, MCFA content in coconut oil
is high; of the oil fraction 3.4–15% is composed of caprylic
acid (C8:0), 3.2–15% of capric acid (C10:0) and 41–56% of
lauric acid (C12:0). High contents of caprylic (2.4–6.2%),
capric (2.6–7.0%) and lauric acid (41–55%) can also be
found in palm kernel oil (Young, 1983). Cuphea seeds
(family of loosestrife) have a broad species-dependent
diversity in MCFA. Oil from Cuphea seeds is a source with
extraordinarily high content of MCFA, showing a remark-
able diversity in composition between species (Graham
et al., 1981). Cuphea lanceolata and Cuphea ignea oils
containing over 80% capric acid and only small amounts
of caprylic acid have been used in studies as sources of
MCTs in piglets (Dierick et al., 2003).
Digestion, absorption and enterocyte metabolism
of MCFAs
As a result of their chemical and physical properties, MCTs
differ significantly from long-chained triglycerides (LCTs)
with regard to digestion, absorption and metabolism.
Due to the relative insolubility of LCT and long chain
fatty acid (LCFA), bile salts play a significant role in
the emulsification of LCT, permitting efficient hydrolysis
by pancreatic lipases and the formation of micelles
containing LCFA and monoglyceride digestion products.
Micelles deliver these products to the brush border
membrane permitting passive diffusion into the enterocyte.
Re-esterification of LCFA and monoglycerides to trigly-
cerides takes place within the enterocytes. The re-formed
Table 1. Chemical properties of caproic, caprylic, capric
and lauric acids
Fatty acid
Molecular
weight (Da)
Melting
point (C) pK
a
Caproic acid (C6:0) 116.2 3.4 4.88
Caprylic acid C8:0) 144.2 16.7 4.89
Capric acid (C10:0) 172.3 31.9 4.89
Lauric acid (C12:0) 200.3 44.0 5.13
pK
a
, negative logarithm of the acid dissociation constant.
References: HSDB (2011), Hsiao and Siebert (1999).
84 J. Zentek et al.
triglycerides reach the lymph, the thoracic duct and finally
the bloodstream via water-soluble lipoproteins (chylomi-
crons).
The hydrolysis of MCTs occurs rapidly in comparison
with that of LCTs and due to higher water solubility,
without the necessity for emulsion with bile. Lingual
and gastric lipases are initially active against MCT in the
stomach generating significant MCFAs and monoglycer-
ides prior to release into the duodenum. With the addition
of pancreatic lipases in the duodenum, MCFAs are made
rapidly available for absorption in the upper small intestine
(Ramirez et al., 2001). Most of the MCFAs are absorbed by
passive diffusion in their free form, but absorption as
acylester was also demonstrated (Carvajal et al., 2000).
Within the enterocyte, MCFAs have a low affinity for fatty
acid binding protein and are therefore largely not re-
esterified but diffuse in to portal blood and associate with
albumin for transport directly to the liver (Bloch, 1974;
Guillot et al., 1993, 1994). Only a small portion of the
MCFAs is taken up by the chylomicrons (Greenberger and
Skillmann, 1969; Bach and Babayan, 1982).
Hydrolysis of MCT may not be necessary for absorption
to occur. In the presence of a digestive disorder such as
pancreatic insufficiency, intact MCTs are partially taken
up by the enterocytes and cleaved hydrolytically within
the cells (Playoust and Isselbacher, 1964; Valdivieso,
1972). Evidence for this differentiated absorptive mechan-
ism was found in experiments using fistulated pigs, as a
biphasic concentration curve was observed in the portal
blood subsequent to repeated infusions of MCTs into
the duodenum. An initial increase in concentration was
observed 15 min after the infusion was administered,
probably indicating the direct absorption of MCFAs. The
second peak was detected after 75–95 min, indicating a
slower process, for instance, direct absorption of MCTs by
enterocytes and subsequent hydrolysis in the enterocyte
(Guillot et al., 1993, 1994).
Intermediary metabolism of MCFAs
It is clear that the majority of MCFAs are efficiently used for
energy production by mitochondrial b-oxidation
after portal transport to the liver (Wojtczak and
Scho
¨nfeld, 1993; Turner et al., 2009). Most of the absorbed
MCFAs are bound to serum albumin with a high affinity
and capacity during direct transport to the liver in portal
blood (Ashbrook et al., 1972; Kenyon and Hamilton, 1994).
Once in the liver, the MCFAs can pass through the
mitochondrial membrane independently of the carnitine
palmitoyltransferase (Sidossis et al., 1996; Rasmussen et al.,
2002). Before oxidation, the MCFAs are activated by the
medium-chain octanoyl-CoA synthetase, stimulated by
carnitine in piglets (van Kempen and Odle, 1993). Since
MCFA freely enter hepatocyte mitochondria compared to
LCFA, they are thought to be more prone to ketone body
synthesis (Odle, 1997) resulting in increased plasma
ketones that may serve as energy substrate for peripheral
tissues. Swine are able to activate MCFAs to CoA thioester
in colonocytes using the MCFA:CoA ligase, and to utilize
them in their intestinal epithelium for energy production
(Vessey, 2001). Due to the low concentrations in the
digesta arising from fermentation, the contribution of
MCFA to the energy supply of the distal epithelium is
probably of minor significance compared to butyrate, the
main energy yielding substrate. Depending on substrate
availability, intramitochondrial b-oxidation results in
energy production and represents the main metabolic
pathway of the MCFAs (Bach and Babayan, 1982; Odle,
1997). A small portion of absorbed MCFA is stored in
adipose tissue (Sarda et al., 1987) or is elongated to LCFAs
and serves to resynthesize triglycerides (Hill et al., 1990;
Carnielli et al., 1996).
Studies on energetics in newborn piglets clearly
demonstrated a superior energetic exploitation of the
MCFAs in comparison with the LCFAs. Compared with
values obtained subsequent to the feeding of LCTs, the
plasma concentrations for 3-hydroxybutyric acid
increased more significantly after the application of
MCT (Odle et al., 1989). In 1-day-old piglets, the plasma
concentration of hydrobutyric acid thereby is negatively
correlated with the chain length. Odd chain MCFA
(C7–C9) were utilized more efficiently by hepatocytes
than C8 and especially C10, probably due to the effects
on propionyl-CoA metabolism (Odle et al., 1991b).
Results from in vitro studies using isolated hepatocytes
support these findings, indicating that the metabolism is
dependent on chain length, as shorter fatty acids were
metabolized to CO
2
as well as other degradation products
such as ketone bodies 40% more rapidly compared with
longer-chain fatty acids (Odle et al., 1991a).
MCFAs as energy sources in piglets
MCFAs represent immediately available sources of energy
that can be supplemented to the diets of neonates
and young animals to improve their energy supply. In
patients, MCFAs are administered in the treatment of
diseases such as lipid absorption disorders, malabsorption
syndromes, pancreatic insufficiency, disorders of the
gall bladder, gastroenteritis, diabetes mellitus and as a
source of energy in premature babies (Borum, 1992;
Heird et al., 1992). A high postnatal capacity to oxidize
fatty acids was identified in many species including new-
born and young piglets (van Kempen and Odle, 1993;
Odle et al., 1994; Heo et al., 2002). These energy-
providing properties of MCTs are of high interest for the
nutrition of young pigs.
The feeding of MCTs to sows in the late gestation phase
in comparison with LCTs increased the survival rate of
neonatal piglets (Newcomb et al., 1991; Azain, 1993; Jean
and Chiang, 1999). In one study, supplementation of
gestating sows with diets containing 10% MCTs (weight
Nutritional and physiological role of medium-chain triglycerides and fatty acids 85
basis) did not result in changes in the birth weights or the
number of live piglets per sow but did increase the
survival rate of the piglets after 3 days of age and beyond
the weaning phase. Improvement in survival rate was
greatest in piglets with a birth weight of less than 900 g
(Azain, 1993). Further, increased blood glucose levels on
the day of birth indicated improved energy status of the
piglets, possibly accounting for the increased neonatal
survival rate.
Given the metabolism of MCFA by liver and limited
inclusion in chylomicrons, supplementation of lactating
sows with MCT would be unlikely to markedly impact on
milk MCFA content as a means of supplementing suckling
pigs. Accordingly, MCT-supplemented diets only led to
minor changes in the milk fat composition, indicating that
no connection could be established between the MCFA
content in the milk of the sows and the increased survival
rate of the piglets (Azain, 1993). The direct application of
MCTs to suckling piglets resulted in an improved energy
balance in neonatal animals; however, the survival rate of
the piglets may not be improved (Odle, 1997).
In weaned pigs, the combined dietary supplementation
of MCTs with different lipases resulted in an increase in
the daily live weight gain (Dierick et al., 2002). An
examination of the effects of various sources of fat (MCT,
soybean oil and animal fat) on weight gain, feed intake
and feed conversion demonstrated that the dietary
inclusion of 5% MCTs (weight basis) within the first
14 days post-weaning provided the greatest increase in
weight gain and a better feed conversion of the piglets
(Dove, 1993). In contrast, the formulation of diets with
free MCFAs in this context often led to a reduction in feed
intake (Odle et al., 1991a, b; Decuypere and Dierick,
2003). The intense, goatish smell of the non-esterified free
fatty acids and the low tolerance to changes in taste may
be factors that contribute to decreased acceptance
(Decuypere and Dierick, 2003). In an experiment with
21-day-old piglets 8% lipids from a medium-chain free
fatty acid mixture (60% C 8:0, 40% C 10:0) were compared
with beef tallow. Although this level of MCFA must have
resulted in an extremely strong odor, compared to a beef
tallow group, feed intake was reduced by only 4% while
growth rate was 6.3% better (Cera et al., 1989).
Furthermore, the MCFAs can induce the secretion of
cholecystokinin and possibly other intestinal hormones,
which influence the feeling of satiety and therefore feed
intake (Mabayo et al., 1992). However, more recent
studies attribute only a minor influence of the MCFAs on
the secretion of cholecystokinin (Symersky et al., 2002).
Influence of MCFAs on the intestinal morphology and
physiology and on the gut-associated immune system
The transitional reduction of intestinal integrity in the
piglet post-weaning is associated with decreased digestive
capacity, mainly due to shorter villi in the small intestine
and reduced digestive enzyme activity (Miller et al., 1986;
van Dijk et al., 2002; Montagne et al., 2007). The mor-
phological and physiological changes are reflected in a
decline in growth rates, an increased susceptibility to
enteric diseases and immunosuppression (Bailey et al.,
1992; Lalles et al., 2007). MCFAs can be utilized directly by
the enterocytes for energy production and thereby help to
support the integrity of the intestinal tissue in post-
weaning piglets (Guillot et al., 1993). Feeding of MCTs to
rats positively influenced the intestinal morphology, re-
sulting in an augmentation of mucosa, a higher phos-
pholipid/protein ratio in jejunal mucosal microvillus
lipids, longer intestinal villi and shorter crypts, and
increased activity of membrane-bound enzymes (Takase
and Goda, 1990). Similar results were achieved using
MCFAs in swine; a significant increase in the length of the
villi in the small intestine combined with a lower crypt
depth and a lower number of intraepithelial lymphocytes
(IELs) were observed (Dierick et al., 2003). Villus length
and crypt depth are often used as indicators for the
evaluation of the mucosal turnover. A reduced number of
IELs could reflect a lower apoptosis rate and be associated
with the increase in villus length and the decrease in crypt
depth or altered immune surveillance. However, little is
known about the influence of MCFAs on gut-associated
and systemic immune reactions and the results do not
allow a concise conclusion on the direction of immuno-
modulatory mechanisms.
MCFAs can act as ligands for the orphan receptor
GPR84, a signaling protein highly expressed in immune
cells. The activation of GPR84 in monocytes and macro-
phages enhanced lipopolysaccharide (LPS)-stimulated
interleukin (IL)-12 p40 production, indicating a mech-
anism linking free fatty acids with immune reactions
(Wang et al., 2006). Although MCFAs are readily absorbed
in the upper intestine, colonic cells were used to study
the impact of MCFA on ILs. Capric acid enhanced IL-8
production in human Caco-2 cells (Tanaka et al., 2001),
while caprylic acid and MCT suppressed IL-8 secretion
in Caco-2 cells after 24 h preincubation by inhibition
of the IL-8 promoter (Hoshimoto et al., 2002). Rats
fed MCTs through a feeding tube showed a significant
increase in the expression of IL-6, followed by the
secretion of immunoglobulin A (IgA) after the injection
of bacterial LPS (Kono et al., 2004). In the same study,
the LPS-induced expression of proinflammatory cytokines
and chemokines (tumor necrosis factor-a(TNF-a), IL-18,
macrophage inflammatory protein-2 and monocyte
chemoattractant protein-1) was significantly lowered
by MCTs and the expression of the immune modulating
and anti-inflammatory cytokine IL-10 in the ileum and
Peyer’s patches was significantly greater in the MCT
group. The expression of interferon-g(IFN-g) was
also blunted by MCTs. The secretion of IgA and the
modulation of the cytokine release subsequent to the
LPS injection were suggested to mediate positive effects
on the intestinal health of the animals (Kono et al., 2004).
86 J. Zentek et al.
Dendritic cells isolated from the thoracic duct lymph
showed similar phagocytic activity independently
whether long-chain (arachidonic or oleic acid) or caprylic
acid was added to an ex vivo culture, but the long-chain
fatty acids suppressed Major Histocompatibility Complex
(MHC) class II molecule expression. This might be
considered as an indicator of better antigen presentation
ability and immune response of the gut-associated
lymphatic tissue when MCFAs are fed (Tsuzuki et al.,
2006). Murine-stimulated IELs had reduced IFN-gproduc-
tion when exposed to long-chain fatty acids, while
caprylic acid did not cause changes in IFN-gproduction
(Hara et al., 2003). In piglets, a mixture of MCFA (caprylic
and capric acid in a mixture at 0.15% in the diet) did not
affect the phagocytic activity of isolated blood-neutrophils
or the relative proportions of CD4
CD8
+
, CD4
+
CD8
and
CD4
+
CD8
+
lymphocytes and MHC
CD21
+
, MHC
+
CD21
and MHC
+
CD21
+
cells in the blood or the mesenteric
lymph nodes. Ileal tissue samples from piglets fed
MCFA did not display changes in mRNA expression of
makrophage inflammatory protein (MIP1-b), IL-1b, IFN-g,
TNF-aand monocyte chemoattractant protein (MCP-1)
compared to control animals (Buchheit, 2009).
Influence of MCFAs on the intestinal microbiota
Due to their antibacterial effects, MCFAs were initially
used in the preservation of feed, specifically in silage
(Woolford, 1975) and foods (Freese et al., 1973). Many
in vitro studies have evidenced that MCFAs and their
monoglycerides are able to inactivate pathogenic bac-
teria, viruses and parasites. MCFA were mainly considered
to be anionic surfactants, which, as a result of this
property, have antibacterial effects (Mroz et al., 2006).
Membrane destabilization by the incorporation of MCFAs
into the bacterial cell wall and cytoplasmic membrane,
as well as the inhibition of bacterial lipases, which
are necessary for the colonization of the skin and the
intestinal mucosa, may be the cardinal mechanisms
(Isaacs et al., 1995; Bergsson et al., 1998, 2002). Changes
in the elementary bodies, the infectious particles, were
detected by electron microscopy following the treatment
of Chlamydia trachomatis with monocapring; however,
the host cell was not impaired (Bergsson et al., 1998).
Besides the direct lytic effects of MCFA, the activation
of bacterial autolytic enzymes might also play a role in
the activity against pathogens (Tsuchido et al., 1985).
Alternatively, the uptake of undissociated fatty acids
into the bacterial cell appears to have cytotoxic effects.
The MCFAs dissociate into protons and anions in the basic
cytoplasm of the cell, decreasing the pH. Cytoplasmic
enzymes are inactivated as a result, leading to the death of
the bacterial cell (Freese et al., 1973; Hsiao and Siebert,
1999). In vitro studies showed a negative correlation
between increasing pH values and the efficacy of the
MCFAs, indicating that the antibacterial effects depend on
the degree of dissociation of the fatty acids. The
undissociated form generally has stronger effects. The
pH of the surrounding environment is therefore of
considerable importance and appears to significantly
influence the efficacy of the MCFAs (Hsiao and Siebert,
1999; Sun et al., 2002). It can be assumed that the
antibacterial effect of the MCFAs in the gastrointestinal
tract is limited to the stomach and the proximal small
intestine (duodenum), as MCFAs are rapidly absorbed
and predominantly found in the dissociated form at
neutral pH. The undissociated form is found at pH
between 3 and 6 (Dierick et al., 2002). Therefore, it can be
speculated that targeted acidification of the stomach, for
instance, by using diets with low buffering capacity and
including organic acids may improve the antibacterial
effects of MCFAs.
In vitro studies have demonstrated that MCFAs and
their monoglycerides inactivate bacteria, viruses and
parasites. The results of these studies are shown in
Tables 2–4 for caprylic and capric acid.
The results summarized in Tables 2–4 are partly
contradictory. In most studies, caprylic and capric acid
were effective against a number of Gram-positive bacteria
species. However, efficacy of these acids against Gram-
negative bacteria was observed only rarely and incon-
sistently. In addition, many studies found lauric acid
(C12:0) to have a pronounced antibacterial effect, which
in some cases surpassed the effects of the other free fatty
acids (Canas-Rodriguez and Smith, 1966; Sun et al., 2002).
Lauric acid is especially effective against Gram-positive
bacteria. The monoglycerides of capric and lauric acid
seemed considerably more effective against bacteria than
were their free fatty acids in a number of studies (Kabara
et al., 1972; Bergsson et al., 1998, 1999, 2002; Petschow
et al., 1998; Sprong et al., 1999). Results for relevant
pathogenic bacteria such as Escherichia coli and Salmo-
nella Enteritidis, the former being specifically important
for weaned piglets, are highly inconsistent, which is most
likely the result of the use of different concentrations,
culture media, strains of bacteria and pH values. For
example, in one study, caprylic and capric acids had no
effect on Gram-negative bacteria at a concentration of
6.93 mM (Kabara et al., 1972). However, others attained
a significant reduction of E. coli and Salmonella Enteritidis
using capric acid at a concentration of 0.5 mM (Sprong
et al., 2001). In contrast, the minimum inhibitory concen-
tration of caprylic acid for E. coli was reported as 12 mM
(1.73 g/l) (Hsiao and Siebert, 1999). Caprylic acid was
effective at inhibiting Salmonella Enteritidis only at higher
concentrations (10 mM) (van Immerseel et al., 2004).
In combination, caprylic and capric acids have syner-
gistic effects. Under simulated pig gastric conditions a
total concentration of 0.35 g MCFAs (C8:0+C10:0) per
100 g medium at a pH of 5 resulted in a decline of the
bacterial flora by 1-log; the proportions of the individual
fatty acids were not crucial for the efficacy (Dierick et al.,
2002). The inhibition of Salmonella Typhimurium and
Nutritional and physiological role of medium-chain triglycerides and fatty acids 87
Table 3. Overview of the effects of caprylic and capric acids on selected Gram-negative bacteria in in vitro experiments
Bacterium
Caprylic
acid
Concentration
(mM)
Capric
acid
Concentration
(mM) Reference
Escherichia coli 0.5 + 0.5 Sprong et al. (2001)
ND ND Petschow et al. (1998)
6.93 6.93 Kabara et al. (1972)
+/ND +/ND Canas-Rodriguez and
Smith (1966)
+ 2.1 (MIC) ND 2.0 Hsiao and Siebert (1999)
2.0 ND Sheu and Freese (1973)
<2 (MIC) ND ND Sun et al. (2002)
Salmonella Enteritidis 0.5 + 0.5 Sprong et al. (2001)
5.0 5.0 Sprong et al. (1999)
+ 10.0 + 5.0 van Immerseel et al. (2004)
Campylobacter jejuni 0.5 + 0.5 Sprong et al. (2001)
Vibrio cholerae ND ND Petschow et al. (1998)
Chlamydia trachomatis 10.0 + 10.0 Bergsson et al. (1998)
Helicobacter pylori + 10.0 + 2.5 Bergsson et al. (2002)
5.0 5.0 Petschow et al. (1998)
Neisseria gonorrhoeae 2.5 +/2.5 Bergsson et al. (1999)
Proteus vulgaris 6.93 6.93 Kabara et al. (1972)
Proteus mirabilis 6.93 6.93 Kabara et al. (1972)
Proteus rettgeri 6.93 6.93 Kabara et al. (1972)
Serratia marcescens 6.93 6.93 Kabara et al. (1972)
Klebsiella pneumoniae <2 ND ND Sun et al. (2002)
+, Inhibition; , no inhibition; +/, marginal inhibition; ND, no data; MIC, minimal inhibitory concentration.
Table 2. Overview of the effects of caprylic and capric acids on selected Gram-positive bacteria in in vitro experiments
Bacterium
Caprylic
acid
Concentration
(mM)
Capric
acid
Concentration
(mM) Reference
Staphylococcus aureus 6.93 + 2.9 (MIC) Kabara et al. (1972)
+ ND + ND Canas-Rodriguez and
Smith (1966)
Staphylococcus epidermidis 6.93 + 2.9 (MIC) Kabara et al. (1972)
alpha-hemolytic streptococci 6.93 + 2.9 (MIC) Kabara et al. (1972)
Group D-streptococci 6.93 + 5.8 (MIC) Kabara et al. (1972)
Streptococcus faecalis +/ND +/ND Canas-Rodriguez and
Smith (1966)
Bacillus subtilis + 1.12 (MIC) ND ND Hsiao and Siebert (1999)
+ 2.0 + 2.0 Sheu and Freese (1973)
Bacillus cereus + 0.47 (MIC) ND ND Hsiao and Siebert (1999)
Micrococcus ssp. 6.93 + 2.9 (MIC) Kabara et al. (1972)
Nocardia asteroides 6.93 + 1.45 (MIC) Kabara et al. (1972)
Corynebacterium ssp. 6.93 + 1.45 (MIC) Kabara et al. (1972)
Pneumococcus ssp. 6.93 + 1.45 (MIC) Kabara et al. (1972)
Listeria monocytogenes 0.5 + 0.5 Sprong et al. (2001)
+ 5.0 + 0.5 Sprong et al. (2001)
Lactobacillus acidophilus + ND + ND Canas-Rodriguez and
Smith (1966)
Lactobacillus fermentum + 11.0 (MIC) ND ND Hsiao and Siebert (1999)
Lactobacillus plantarum + 18.2 (MIC) ND ND Hsiao and Siebert (1999)
Clostridium perfringens + ND + ND Canas-Rodriguez and
Smith (1966)
Enterococcus faecium + <2 mM (MIC) ND ND Sun et al. (2002)
Enterococcus faecalis + <2 mM (MIC) ND ND Sun et al. (2002)
Enterococcus casseliflavus + <2 mM (MIC) ND ND Sun et al. (2002)
+, Inhibition; , no inhibition; +/, marginal inhibition; ND, no data; MIC, minimal inhibitory concentration; mM,
millimoles per liter.
88 J. Zentek et al.
coliforms by 15 mM caprylate was also demonstrated
using a porcine continuous culture system, simulating the
porcine caecum; bifidobacteria and streptococci were less
affected (Messens et al., 2010).
MCFA activities described in vitro were also character-
ized in feeding studies in milk-fed animals. During the
search for antimicrobial factors in milk, it was found that
rabbit milk fat, having about 40% MCFAs (Maertens,
1998), neutralized bacteria isolated from the stomach,
with caprylic and capric acids showing the highest
activity. No effect could be observed in the digesta of
the small intestine (Canas-Rodriguez and Smith, 1966).
Milk fat of the rabbit showed a higher antibacterial
effect against Staphylococcus aureus,Candida albicans,
Lactobacillus acidophilus and Clostridium perfringens,in
comparison with E. coli and Streptococcus faecalis.
Other in vitro studies confirmed the antibacterial
activities using MCTs in combination with lipases in a
test model involving weaned piglets. A 10-fold reduction
of the total anaerobic bacteria plate count, and viable
counts for lactobacilli and E. coli was achieved in the
digesta of the stomach and duodenum by MCFAs and
microbial lipase (Dierick et al., 2002). Besides the effects
on the luminal bacteria, it seems interesting to consider
the impact on bacterial adherence. Sodium caproate
was found to prevent the adhesion to and subsequent
invasion of the ileal mucosa in rats by Salmonella
Typhimurium (Cox et al., 2008). Furthermore, this study
demonstrated a bactericidal effect against Salmonella
Typhimurium, depending on the concentration of the
MCFA. After the simultaneous oral application of capric
acid and Vibrio cholerae to mice, the pathogen could
not be detected in the ileum or the caecum, suggesting
a potential prophylactic use against intestinal infections
(Petschow et al., 1998). Two reports suggest that
Campylobacter infection can be controlled in poultry
by feeding caprylic acid beginning at 1 day of age (Solis
de Los Santos et al., 2008, 2010).
Effects on performance of piglets
The potential use of MCFAs as rapidly available and
easily metabolizable sources of energy has been exam-
ined in the feeding of pigs in which the MCFAs
were usually administered as intact MCTs in the feed.
Performance of artificially reared suckling piglets
was reduced using a diet containing 24% but not 13.5%
MCTs (Newport et al., 1979). The results of studies
using weaned piglets have been inconsistent. No differ-
ences occurred with regard to feed intake, feed effici-
ency and weight gain when comparing a diet with 10%
MCTs versus diets containing the same amount of
tallow, pig fat or corn oil (Allee et al., 1972). In contrast,
significantly higher (6–8% in average) growth rates
were found for the MCTs in a study comparing rations
with three different copper levels and 5% lipid from
MCT with soya oil or animal fats (Dove, 1993). Also, a 10%
increase in the daily weight gain was found in piglets
fed 2.5% MCTs selectively processed from coconut
oil (enriched for capric acid) compared to soybean
oil (Dierick et al., 2002). The growth response was
observed for MCTs whether or not it was supplemented
with lipase, although addition of lipase resulted in more
dramatic effects on gastric and duodenal bacterial
populations.
Although the evidence for the favorable energetic
attributes of MCT is strong, many authors consider that
the mechanisms resulting in improved piglet performance
are associated with the antibacterial effects of the
MCFAs in the intestinal lumen, specifically against
pathogenic strains (Decuypere and Dierick, 2003). Others
have associated performance effects with the direct
and indirect influence of MCFA on epithelial function
(villus length, crypt depth) in the upper small intestine.
An increased absorptive surface could facilitate increased
uptake and a more efficient utilization of nutrients for
growth.
Table 4. Overview of the effects of caprylic and capric acids on viruses, Candida albicans and Giardia lamblia in in vitro
experiments
Test organism
Caprylic
acid
Concentration
(mM)
a
Capric
acid
Concentration
(mM)
b
References
Respiratory syncytial virus +/15 + 30 M Isaacs et al. (1995)
Herpes simplex virus +/15 + 30 Isaacs et al. (1995)
ND ND + 22 Thormar et al. (1987)
Vesicular stomatitis virus + 69 + 22 Thormar et al. (1987)
Visna virus + 69 + 22 Thormar et al. (1987)
C. albicans 6.93 + 2.9 Kabara et al. (1972)
+ ND + ND Canas-Rodriguez
and Smith (1966)
Giardia lamblia +/>4.00 mMLD
50
+ 500–2000 mMLD
50
Reiner et al. (1986)
a
Except for G. lamblia, where the data are expressed as mM for the LD
50
.
b
Except for respiratory syncytial virus, where the data are expressed as M and for G. lamblia, where the data are expressed as
mM for the LD
50
.
+, Inhibition; , no inhibition; +/, marginal inhibition; ND, no data available; mM, millimoles per liter; mM, micromoles per
liter; LD
50
, median lethal dose.
Nutritional and physiological role of medium-chain triglycerides and fatty acids 89
Toxicity of MCFAs
Many studies have investigated potential oral, parenteral
and dermal toxicity using laboratory animals and humans;
however, the findings have unanimously indicated a low
toxicity. Diets containing MCTs comprising up to 15% of
the calories or up to 50% of the total fat are considered
to have a low toxicity or to be non-toxic (Traul et al.,
2000). In neonatal piglets, these effects may be ketogenic
or narcotic (Lin et al., 1995). To date, no indications have
been found for an allergenic potential. However, the
application of higher doses led to weak irritation of the
mucosa of the eyes and the skin (Traul et al., 2000).
Stagnation in growth and morphological changes were
observed in mammalian cell cultures (HeLa, human
fibroblasts and murine neuroblastoma cells) treated with
millimolar concentrations of C6:0 and C10:0 fatty acids,
which may be the result of structural alterations of the cell
membrane (Sheu et al., 1975). The results of the in vitro
studies are important for the characterization of potential
toxic effects. However, it must be noted that the results
of in vitro models cannot be readily extrapolated to
in vivo situations. The cytotoxic effects that have been
mentioned may not be of consequence in the living
organism as possible negative side effects may be
neutralized by the complex interactions of physiological
factors such as digesta, mucins and serum.
Conclusion
In conclusion, MCFAs and MCTs can be used in piglet
nutrition to improve performance parameters including
piglet survival, feed intake and feed-to-gain ratio. Inclu-
sion levels of MCTs up to 15% are possible, whereas
dietary addition of free MCFA is limited due to their
negative sensory effects. Inclusion levels of 8% were
described in diets for young pigs. There is good evidence
indicating that MCFAs offer a highly available and efficient
energy source as compared to LCT associated with their
passive absorption, portal transport to liver and efficient
oxidation. The contribution of the antimicrobial and
immunomodulatory properties of MCFAs to the observed
performance responses are less clear and may warrant
further characterization.
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Nutritional and physiological role of medium-chain triglycerides and fatty acids 93
... They occur in nature in the form of triglycerides in milk and various vegetable fats such as palm or coconut oil. These products are of interest in ABF production systems 1) as a highly available source of energy, helping the young pig successfully transition at the time of weaning and possibly providing growthpromoting benefits, 2) as an antimicrobial in the diet of the pig, 3) as compounds which help to maintain favorable intestinal architecture, and 4) as a means of controlling pathogens in the feed such as African Swine Fever virus, Porcine Epidemic Diarrhea virus, and Salmonella (Zentek et al., 2011). This latter role will be addressed later in this manuscript. ...
... Higher levels have been employed, but the results have been disappointing (Allee et al., 1972). Overall, their impact on the performance of young pigs has been inconsistent, and more research in vivo is required, especially under commercial conditions (Zentek et al., 2011;Hanczakowska, 2017). Feeding medium-chain triglycerides to pregnant sows has been proposed as a strategy to improve livability in gilt offspring; the most recent research suggests this is not a likely outcome, at least not under the conditions of this particular trial (Craig et al., 2019). ...
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The discovery of the use of antibiotics to enhance growth in the 1950’s proved to be one of the most dramatic and influential in the history of animal agriculture. Antibiotics have served animal agriculture, as well as human and animal medicine, well for more than seven decades, but emerging from this tremendous success has been the phenomenon of antimicrobial resistance. Consequently, human medicine and animal agriculture are being called upon, through legislation and/or marketplace demands, to reduce or eliminate antibiotics as growth promotants and even as therapeutics. As explained in this review, adoption of antibiotic-free pork production would represent a sea change. By identifying key areas requiring attention, the clear message of this review is that success with antibiotic free production, also referred to as “no antibiotics ever,” demands a multifaceted and multidisciplinary approach. Too frequently, the topic has been approached in a piecemeal fashion by considering only one aspect of production, such as the use of certain feed additives or the adjustment in health management. Based on the literature and on practical experience, a more holistic approach is essential. It will require the modification of diet formulations to not only provide essential nutrients and energy, but to also maximize the effectiveness of normal immunological and physiological capabilities that support good health. It must also include the selection of effective non-antibiotic feed additives along with functional ingredients that have been shown to improve the utility and architecture of the gastrointestinal tract, to improve the microbiome and to support the immune system. This holistic approach will require refining animal management strategies, including selection for more robust genetics, greater focus on care during the particularly sensitive perinatal and post-weaning periods, and practices that minimize social and environmental stressors. A clear strategy is needed to reduce pathogen load in the barn, such as greater emphasis on hygiene and biosecurity, adoption of a strategic vaccine program and the universal adoption of all-in-all-out housing. Of course, overall health management of the herd, as well as the details of animal flows, cannot be ignored. These management areas will support the basic biology of the pig in avoiding or, where necessary, overcoming pathogen challenges without the need for antibiotics, or at least with reduced usage.
... Yoo , and the results showed that RAMPS could significantly enhance T lymphocyte proliferation (43). GML is not only an excellent food emulsifier but also a safe, efficient, and broad-spectrum bacteriostatic agent and has excellent antiviral function, which makes it a potential vaccine immune enhancer (17,(44)(45)(46). Therefore, the purpose of this experiment was to evaluate the immune-enhancing function of oral GML in weaned piglets on PRV-inactivated vaccine. ...
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... [78,79] Consequently, the effect of MCFAs as antibacterial was limited in the stomach and proximal small intestine, as they were quickly absorbed and often found in dissociated form at neutral degree of pH. [80] As the unassociated form exhibited the stronger effect, this was found at pH from 3 to 6. [81] Consequently, targeted acidification of the stomach, for example, by using diets containing organic acids with low buffering capacity, may enhance the antibacterial activity of MCFAs. ...
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... MCFAs as the intestinal energy sources can also improve the growth performance of infants by improving intestinal function. The protective effect of MCFAs and MCT on the intestinal barrier and gut health has been supported in suckling piglets as an in vivo mammalian neonate model (58,59). Studies have demonstrated that MCFAs in milk, especially 8:0, 10:0, and 12:0, have antimicrobial effects against several bacteria, such as Clostridium, Salmonella, and Helicobacter pylori, which might enhance resistance against intestinal pathogens (17,60,61). ...
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... Consequently, it is necessary to balance the lipid content with other nutrients amount in order to satisfy all nutritional requirements. In this context, medium-chain triglycerides (MCTs) are saturated fatty acids with 6 to 12 carbon atoms that appear to be rapidly digested by lipases and transported directly into the bloodstream, as described in pigs by Zentek et al. [3]. These triglycerides have been suggested for companion animals with lipid digestion problems and poor physical condition. ...
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... Besides this, OAs can improve the antibacterial effects of fatty acids (Zentek et al., 2011). The combinations of OA and fatty acids have a beneficial impact on intestinal microecology in piglets (Zentek et al., 2013;Kuang et al., 2015) and nutrient digestibility in laying hens (Lee et al., 2015). ...
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Due to volatility, low solubility and instability, the application of SCFAs and MCFAs is limited, which is expected to be solved by micelles. Taking SCFAs and MCFAs as models, this paper aims to research the influences of alkyl chain length and type on HS15 micelles. The critical micelle concentration (CMC) of various acid-HS15 systems was determined firstly. Then some air-water interface parameters and thermodynamic parameters were analyzed. Subsequently, particle size, cloud points (CP) and fluorophore release curves were measured. With the increase of CMC and Gmin, the decrease of size and CP, and the rapid quenching of fluorophores, it is more difficult for acids with longer-chain to form stable micelles with HS15 because of the strength of iceberg structure. Showing smaller CMC and Gmin, smaller size, higher CP and slower release of fluorescers, branched molecules can bind more closely to the hydrophobic part of HS15 due to their spatial flexibility.
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The binding of hexanoic, octanoic, and decanoic acids to defatted human plasma albumin was measured by equilibrium dialysis at 37° in a calcium-free Krebs-Ringer phosphate buffer, pH 7.4. The results were analyzed in terms of multiple stepwise equilibria. For each of the albumin binding sites, the magnitude of the equilibrium constants increased as the chain length of the acid increased: decanoate > octanoate > hexanoate. The first six equilibrium constants ranged from 1.5 x 10⁴ to 4.7 x 10 for hexanoate, from 3.4 x 10⁴ to 1.2 x 10³ for octanoate, and from 10⁵ to 3.4 x 10³ for decanoate. In each case, the equilibrium constants occurred in a generally descending order, suggesting that major cooperative binding effects do not occur over the physiologically important range of fatty acid-albumin molar ratios. The equilibrium constants calculated for each of the three acids could not be grouped in a common way in terms of classes of binding sites, indicating that a single, uniform class-site binding model cannot be applied to these medium chain fatty acids. Octanoate binding was relatively insensitive to pH changes over the range of 6.0 to 8.2. Decanoate binding also was similar at pH 6.5 and 7.4. A decrease in octanoate binding occurred when the albumin was acetylated or when the medium contained 6 m urea. Octanoate binding also was decreased when either palmitate or oleate was added to albumin, suggesting that medium chain fatty acid transport may be influenced by changes in the plasma long chain free fatty acid concentration.
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Fatty acid analyses of seed lipids in 46 species of Cuphea are presented, representing the first major survey of a molecular nature for the family. A remarkable diversity in composition is found, with seeds containing high amounts of several medium chain fatty acids. Lauric acid (12:0) predominates in 43% of the species studied, constituting 50–74% of the total fatty acid content. Capric acid (10:0) is the dominant fatty acid in 32% of the species, comprising as much as 87% of the total acid content. Caprylic acid (8:0) predominates in one section of the genus. The emphasis on production of fatty acids with carbon chain lengths of 12, ten, and eight carbon atoms is unique among plant genera studied to date. Among seven of the nine sections studied, one pattern of fatty acid composition predominates. Two sections have no characteristic pattern, supporting other evidence of their polyphyletic origin. The most significant systematic contribution is made by comparison of the predominate fatty acid components in the seed lipids. When used in conjunction with floral morphology, pollen studies, and chromosome number, it provides an important new basis on which to draw inferences of evolution and clarify present relationships within the genus. Additionally, a trend from the longer-chained, unsaturated linoleic acid (18:2) as a major lipid component to shorter-chained saturated capric and caprylic acids is correlated with increasing floral specialization. It is suggested that mutations in regulatory genes have occurred which cause fatty acid production in seeds to cease at progressively earlier stages, resulting in accumulation of large amounts of single fatty acids of progressively shorter carbon chain lengths.
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Two experiments were conducted to study the efficacy and causes of medium-chain triglycerides (MCT) in sow diet in improving the survival of neonatal pigs. In Experiment 1, beginning on d84 of gestation and continuing through d28 of lactation, 51 sows were fed corn-soybean meal diet mixed with either soybean oil (SO; n=17), coconut oil (CO; n=18), or MCT (n=16) in a proportion of 9:1 by weight. The highest improvement in survival of pigs by sows fed MCT (p<0.01) or CO (p<0.05) was observed during the first three days after birth in pigs weighing <1100 g at birth, compared with sows fed SO. Their three-day survival was 98.6, 80.0 and 47.6%, respectively, for MCT, CO and SO groups. In Experiment 2, beginning on d84 of gestation and continuing through farrowing, 24 sows, 8 sows per treatment, were fed diets as in Experiment 1. Liver glycogen content of pigs 4 h after born from sows fed MCT (p<0.10) and CO (p<0.01), and muscle glycogen of pigs from sows fed MCT (p<0.01) and CO (p<0.10) were increased, compared to those of pigs from sows fed SO. Plasma albumin was increased by MCT and CO (p<0.01), relative to SO. The results suggest that MCT or CO in sow diets may enhance the body glycogen stores and maturity of pigs at birth and, hence, their survival, particularly in pigs with low birth weight during the first three days of life.
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The chapter discusses carboxylic acids as bioregulators and gut growth promoters in nonruminants. The chapter presents a review of current literature relating the modes of action and effectiveness of both short and medium chain carboxylic acids relative to gut health and performance of nonruminant animals, with an emphasis on pigs. Over the past 50 years numerous studies have been addressed worldwide to evaluate four major benefits because of carboxylic acids: (1) improved health and resistance to disease, (2) faster growth, (3) increased efficiency of diet utilization, (4) better carcass quality. Secondary effects, concerning environmental pollution (less total N, volatilized ammonia, P) and/or reduced production costs have also received considerable attention. The chapter discusses the intraluminal and post-absorptive bioactivity of short-chain fatty acids (SCFA) and medium-chain fatty acids (MCFA) in nonruminants, and particularly in pigs. The chapter discusses: (1) Some essentials on the physicochemical properties of SCFA and MCFA, (2) intraluminal production rates and concentrations in particular sections of the gut, (3) direct and/or indirect effects of SCFA and MCFA on gut functionality, (4) transepithelial transport and absorptive mechanisms of SCFA, and (5) post-absorptive roles in metabolic and regulatory processes of the body.
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Fat digestion and absorption in the stomach and small intestine, metabolism of fatty acids in the liver and effects of dietary fat composition (carbon chain length, odd–even number of carbon atoms, distribution of fatty acids in triacylglycerols and degree of saturation of fat) in piglets are reviewed. At the same time, the nutritional factors which affect fat metabolism in piglets are discussed. The nutritional factors included betaine, choline, methionine, carnitine, lecithin, and dietary fat level for sows and milk fat content.
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A comprehensive study of how age and weaning affect intestinal structure and enterocyte ability to digest and absorb nutrients has been carried out in 4- and 6-week-old piglets. Villus length, which did not change significantly in unweaned piglets 4–6 weeks after birth, was halved 5 days after weaning. Crypt depth, which increased normally in unweaned piglets, is further increased by weaning in both 4- and 6-week-old animals. Lactase activity, which decreased normally with age, was inhibited more than a-glucosidase by weaning. Weaning of 6-week-old piglets also caused a significant increase in maltase II and III activities. Alkaline phosphatase activity was unaffected by age or weaning in 4- and 6-week-old piglet intestine. Na-dependent alanine transport was reduced in 6- compared with 4-week-old unweaned piglet intestine. Weaning inhibited Na-dependent alanine transport in 4- but not 6-week-old pigs. Na-independent alanine transport, which was considerably less than that found in the presence of Na, was not noticeably affected by age or weaning. Weaning-induced problems in intestinal function appear from the present results to be caused more by changes in intestinal structure and specific loss of digestive enzymes rather than by any gross change in absorptive function. The possible role of immune as well as nutritional factors in causing these weaning-dependent changes in intestinal function is discussed.
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1. The butterfat in a whole-milk diet was replaced by either beef tallow, coconut oil or soya-bean oil. The diets contained 280 g fat and 720 g dried skim milk per kg and were supplemented with vitamins A, D, E and K. 2. These diets were offered as a milk, containing 200 g solids/Kg, to pigs weaned at 2 d of age during a 26 d experiment. The pigs were fed at hourly intervals to a scale based on live weight (scale E ). 3. The performance of the pigs and the apparent digestibility of the dietary fats indicated that soya-bean oil was equal to butterfat. Butterfat was slightly superior to coconut oil and markedly superior to beef tallow. 4. The amount and composition of the fatty acids were studied in the proximal, mid and distal portions of the small intestine. When the beef tallow diet was given there was an increased amount of total fatty acids in the digesta of the small intestine, mainly in the distal portion. The digesta contained the smallest quantity of fatty acids when the soya-bean oil diet was given. The fatty acid composition of the digesta indicated that the short- and medium chain fatty acids from all the diets were well utilized, but an increasing proportion of stearic acid occurred in the distal portion of the small intestine. The interpretation of changes in fatty acid composition in the digesta in relation to absorption is discussed.
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Background and Aim: It has been suggested that dietary fat exacerbates intestinal inflammation. We investigated the effect of fatty acids on interleukin (IL)-8 production in a human intestinal epithelial cell line (Caco-2). Methods: The cells were cultured as monolayers on microporous membranes in culture inserts. Oleic acid (OA), capric acid (CA), docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) were applied to the apical compartment of Caco-2 cell monolayers. The concentration of IL-8 in the basolateral medium was measured by using enzyme-linked immunosorbent assay, and the expression of IL-8 mRNA was measured by using competitive reverse transcription–polymerase chain reaction. Protein kinase C inhibitors (GF109203X and calphostin C) and H-7 (a protein kinase inhibitor) were used to study the mechanisms by which IL-8 production is stimulated. Results: Both OA and CA enhanced IL-8 production (approximately fivefold), whereas DHA and EPA did not. Both OA and CA also enhanced IL-1-induced IL-8 production. The onset of OA-induced IL-8 production was delayed compared with that of CA-induced IL-8 production. Both OA and CA enhanced IL-8 mRNA expression (approximately fivefold) after 6 and 3 h, respectively. The protein kinase inhibitor (H-7) reduced both OA- and CA-induced IL-8 production by 88.0 and 85.9%, respectively. The protein kinase C inhibitors (GF109203X and calphostin C) reduced OA-induced IL-8 production by 29.3 and 54.5%, respectively, but showed no effect on CA-induced IL-8 production. Conclusions: These findings suggest that not only OA but also CA stimulates IL-8 production in intestinal epithelial cells, and the mechanisms of action differ between OA and CA.