Nutritional and physiological role of
medium-chain triglycerides and medium-chain
fatty acids in piglets
*, S. Buchheit-Renko
, F. Ferrara
, W. Vahjen
, A. G. Van Kessel
and R. Pieper
Department of Veterinary Medicine, Institute of Animal Nutrition, Freie Universita
¨mmerstrasse 34, 14195 Berlin, Germany,
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
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
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: email@example.com
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
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;
`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.,
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
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
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
point (C) pK
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
, 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-
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
¨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
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
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-
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
lymphocytes and MHC
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
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
+ 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
Staphylococcus aureus 6.93 + 2.9 (MIC) Kabara et al. (1972)
+ ND + ND Canas-Rodriguez and
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
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
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
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
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
Table 4. Overview of the effects of caprylic and capric acids on viruses, Candida albicans and Giardia lamblia in in vitro
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
+ 500–2000 mMLD
Reiner et al. (1986)
Except for G. lamblia, where the data are expressed as mM for the LD
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
+, Inhibition; , no inhibition; +/, marginal inhibition; ND, no data available; mM, millimoles per liter; mM, micromoles per
, 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.
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
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