Potential Use of Silver Nanoparticles as an Additive in Animal Feeding

Abstract

Research included in this work has been funded by Laboratorios Argenol, S.L. (Zaragoza, Spain), through the projects OTRI 2006/0279, OTRI 2007/0640 and DEX-600100-2008-23. J. Ducha (University of Zaragoza), M.A. Latorre (Centro de Investigación y Tecnología de Aragón), J. Prieto and E. Gonzalo have been involved in the experimental research included in this paper.

Full text

Potential use of silver nanoparticles as an additive in animal feeding 325
Potential use of silver nanoparticles as an additive in animal feeding
Manuel Fondevila
X
Potential use of silver nanoparticles as an
additive in animal feeding
Manuel Fondevila
Instituto Universitario de Experimentación en Ciencias Ambientales,
Departamento de Producción Animal y Ciencia de los Alimentos, Universidad de
Zaragoza, M. Servet 177, 50013 Zaragoza
Spain
1. Abstract
Among other uses, metallic silver and silver salts have currently been applied as
antimicrobial agents in many aspects of medical industries, such as coating of catheters,
dental resin composites and burn wounds, as well as in homeopathic medicine, with a
minimal risk of toxicity in humans. However, their use in animal feeding as prebiotics have
remain minimised, mostly because of the low cost antibiotics used as growth promoters in
the second half of the XX Century. However, after the ban of this practice in the European
Community, silver compounds appear as a potential alternative to other already in use,
such as organic acids, oligosaccharides, plant extracts, etc. The major concerns about the safe
use of an additive in animal feeding are its effective role as antimicrobial, acting selectively
over potential pathogens but not over symbiotic microbial communities; a low toxic effect
over the animal and its human consumer; and a low risk of environmental pollution.
Metallic silver nanoparticles (up to 100 nm) allow for a higher antimicrobial effect than
silver salts, are more resistant to deactivation by gastric acids and have a low absorption rate
through the intestinal mucosa, thus minimising its potential risk of toxicity. Besides, it has
been shown that the doses that promote animal physiological and productive effects are
very low (20 to 40 ppm), especially compared to the 10 to 100-fold higher concentration used
with other metallic compounds such as copper and zinc, thus precluding a harmful
environmental effect. This chapter describes the reasons why silver nanoparticles could be
applied to animal feeding, and provides with some available data in this regard. In any case,
its registration as feed additive is a previous requisite before being applied in practical
conditions.
2. Introduction
From the second half of the XX Century, the modern application of technology on animal
production has been associated to the intensification of the applied systems, looking for a
higher economic profitability by reducing the time and increasing the total magnitude of
production. The necessary shortening of the productive cycles and the earlier weaning of
17

Silver Nanoparticles326
animals leads to an increasing of sensitivity of animals, adapted to focus all their
physiological resources to high growth performances and consequently making them more
sensitive to the environmental conditions and the infection by different diseases, not
necessarily of severe gravity, but that in any case produce considerable reductions in
productivity. In terms of animal feeding and nutrition, this situation allowed to the
transition from the concept of giving nutrients to meet the needs for improving growth as
the basic rule to, once this has been assumed, the use of additives to improve productive
performances over nutritive standards by reaching an optimum health status of animals.
Any substance is considered as a feed additive when, not having a direct utilisation as
nutrient, is included at an optimum concentration in diet or in the drinking water to exert a
positive action over the animal health status or the dietary nutrient utilisation. Because of their
chemical nature as active principles, are generally included in very small proportions in diet.
With the onset of the mentioned productive situation, the use of antibiotics as feed additives –
or growth promoters – became predominant over other alternatives, because of their low cost
and high and uniform response. It has to be considered that the use of antibiotics as growth
promoters, given at sub therapeutical levels to all animals and for prolonged periods of time, is
different to their use as therapeutics, administered at higher proportions to sick animals and
only until recovery. Briefly, if a small amount of a substance selectively acts against some
harmful microbial species occasionally established or transient in the digestive tract, thus
controlling the microbial equilibrium of its microbiota, host animals would need to spend less
metabolic effort in the immunological control of the situation. Then they would use the extra
nutrients for other physiological purposes, thus reaching better productive performances. In
this scenario, the magnitude of such growth promoter substances will be highest in young
weaned animals, which low immune development and high growth requirements make them
more exposed to pathological challenges. It has been reported that using antibiotics as growth
promoters in diets increases weight gain and reduces feed to gain ratio (the amount of feed
ingested to reach each unit of weight gain) in pigs by 0.16 and 0.07, respectively (Cromwell,
1991). It has to be noticed that, whereas this concept of host health improvement through
microbial manipulation is generally applied for monogastric animals (pigs, poultry, rabbits,
etc.), it is not totally so for ruminants, where the search of the digestive health interacts with
the presence in former sites of the tract of a large fermentation chamber of extreme importance
for the ruminant physiology.
As it has been shown that the continuous use of antibiotics as growth promoters provoke
the retention in animal tissues and that the human consumption of such animal products
would potentially increase processes of antibiotic resistance, movements of social pressure
towards food security were claiming for a strict control and against their use in animal
feeding, reaching the banning of using antibiotics as growth promoters from 2006 in the
European Community (CE 1831/2003). In other way, the use of some trace elements such as
zinc and copper, that have been systematically included as growth promoters in diets for
weaned piglets because of their beneficial role in pig health status (Hahn & Baker 1993;
Smith et al., 1997) have been also restricted to those levels that satisfy the metabolic needs of
animals because of both their retention in animal tissues and environmental hazard. The
addition of high doses of zinc (from 2500 to 3500 ppm, as zinc oxide) or copper (from 150 to
250 ppm, as copper sulphate) modulates the microbial status of the digestive tract and
reduce the incidence of post-weaning diarrhoea (Jensen-Waern et al., 1998; Broom et al.,
2006), generally promoting increases in productive performances (Hill et al., 2000; Case &
Carlson, 2002). However, it remains unclear to what extent the response is associated with
its role over the digestive microbial ecosystem (Hogberg et al., 2005) or directly over the
piglet metabolism (Zhou et al., 1994), by affecting the secretion and activity of pancreatic
and intestinal digestive enzymes or the maintenance of the morphology of the intestinal
mucosa (Li et al., 2001; Hedemann et al., 2006).
Considerable efforts have been made to look for alternatives to antibiotics growth promoters
in animal feeding during the last three decades. Among the most widely used products in
pig and poultry production can be cited the organic acids (Partanen & Mroz, 1999;
Ravindran & Kornegay, 1993), plant extracts (Cowan 1999; Burt 2004), oligosaccharides
(Mull & Perry 2004) or probiotics (Gardiner et al., 2004).
3. Silver as antimicrobial
Silver compounds have been historically used to control microbial proliferation (Wadhera &
Fung, 2005). The antifungal and antibacterial effect of silver nanoparticles, even against
antibiotic-resistant bacteria (Wright et al., 1994; 1999) has been demonstrated in in vitro
conditions. Nowadays, silver compounds are routinely applied in a wide array of industrial
and sanitary fields, such as coating of catheters and surgery material, the production of
synthetic compounds for odontology, treatment of burn injuries, homeopathic medicine or
water purification (Spencer, 1999; Klasen, 2000; Wadhera & Fung, 2005; Atiyeh et al., 2007;
Hwang et al., 2007).
Traditionally, silver has been used as salts (ionic form), mainly nitrate, sulphate or chloride.
However, silver cation is converted into the less effective silver chloride in the stomach or
bloodstream, and can form complexes with various ligands. Silver nitrate is unstable, and can
be toxic to tissues (Atiyeh et al., 2007). In contrast, metallic silver in form of colloidal solution
or as 5 to 100 nm nanoparticles is more stable to hydrochloric acid, is absorbed at a much
lower extent by euchariotic cells and therefore is minimally toxic, and at the same time exert a
higher antimicrobial effect (Choi et al., 2008), which explains why its use has been promoted in
the last decades (Atiyeh et al., 2007). Lok et al. (2006) showed that, even though silver
nanoparticles and silver ions in form of silver nitrate have a similar mechanism of action, their
effective concentrations are at nanomolar and micromolar levels, respectively.
Silver exerts its antimicrobial activity through different mechanisms. It has been reported to
uncouple the respiratory electron transport from oxidative phosphorylation and to inhibit
respiratory chain enzymes (Schreurs & Rosemberg, 1982; Bard & Holt, 2005). Silver also
adheres to bacterial surface, thus altering membrane functions, leading to a dissipation of
the proton motive force (Percival et al., 2005; Lok et al., 2006), and interacts with nucleic acid
bases, inhibiting cell replication (Wright et al., 1994; Yang et al., 2009). Some authors have
demonstrated its toxic effect over different serovars of Escherichia coli (Zhao & Stevens, 1998;
Sondi & Salopek-Sondi, 2004; Jung et al., 2008) and Streptococcus faecalis (Zhao & Stevens,
1998), but its observed effect over Staphylococcus aureus has been variable (Li et al., 2006;
Kim et al., 2007; Jung et al., 2008). Yoon et al. (2007) observed a higher effect of silver
nanoparticles on Bacillus subtilis than on Escherichia coli, suggesting a selective antimicrobial
effect, possibly related to the structure of the bacterial membrane, although Singh et al.
(2008) assume higher sensitivity of Gram-negative bacteria to treatment with nanoparticles.
The possible effects of metallic silver and silver ions over microorganisms from the digestive
tract are scarcely documented. The selective response of silver in such ecosystem, with a

Potential use of silver nanoparticles as an additive in animal feeding 327
animals leads to an increasing of sensitivity of animals, adapted to focus all their
physiological resources to high growth performances and consequently making them more
sensitive to the environmental conditions and the infection by different diseases, not
necessarily of severe gravity, but that in any case produce considerable reductions in
productivity. In terms of animal feeding and nutrition, this situation allowed to the
transition from the concept of giving nutrients to meet the needs for improving growth as
the basic rule to, once this has been assumed, the use of additives to improve productive
performances over nutritive standards by reaching an optimum health status of animals.
Any substance is considered as a feed additive when, not having a direct utilisation as
nutrient, is included at an optimum concentration in diet or in the drinking water to exert a
positive action over the animal health status or the dietary nutrient utilisation. Because of their
chemical nature as active principles, are generally included in very small proportions in diet.
With the onset of the mentioned productive situation, the use of antibiotics as feed additives –
or growth promoters – became predominant over other alternatives, because of their low cost
and high and uniform response. It has to be considered that the use of antibiotics as growth
promoters, given at sub therapeutical levels to all animals and for prolonged periods of time, is
different to their use as therapeutics, administered at higher proportions to sick animals and
only until recovery. Briefly, if a small amount of a substance selectively acts against some
harmful microbial species occasionally established or transient in the digestive tract, thus
controlling the microbial equilibrium of its microbiota, host animals would need to spend less
metabolic effort in the immunological control of the situation. Then they would use the extra
nutrients for other physiological purposes, thus reaching better productive performances. In
this scenario, the magnitude of such growth promoter substances will be highest in young
weaned animals, which low immune development and high growth requirements make them
more exposed to pathological challenges. It has been reported that using antibiotics as growth
promoters in diets increases weight gain and reduces feed to gain ratio (the amount of feed
ingested to reach each unit of weight gain) in pigs by 0.16 and 0.07, respectively (Cromwell,
1991). It has to be noticed that, whereas this concept of host health improvement through
microbial manipulation is generally applied for monogastric animals (pigs, poultry, rabbits,
etc.), it is not totally so for ruminants, where the search of the digestive health interacts with
the presence in former sites of the tract of a large fermentation chamber of extreme importance
for the ruminant physiology.
As it has been shown that the continuous use of antibiotics as growth promoters provoke
the retention in animal tissues and that the human consumption of such animal products
would potentially increase processes of antibiotic resistance, movements of social pressure
towards food security were claiming for a strict control and against their use in animal
feeding, reaching the banning of using antibiotics as growth promoters from 2006 in the
European Community (CE 1831/2003). In other way, the use of some trace elements such as
zinc and copper, that have been systematically included as growth promoters in diets for
weaned piglets because of their beneficial role in pig health status (Hahn & Baker 1993;
Smith et al., 1997) have been also restricted to those levels that satisfy the metabolic needs of
animals because of both their retention in animal tissues and environmental hazard. The
addition of high doses of zinc (from 2500 to 3500 ppm, as zinc oxide) or copper (from 150 to
250 ppm, as copper sulphate) modulates the microbial status of the digestive tract and
reduce the incidence of post-weaning diarrhoea (Jensen-Waern et al., 1998; Broom et al.,
2006), generally promoting increases in productive performances (Hill et al., 2000; Case &
Carlson, 2002). However, it remains unclear to what extent the response is associated with
its role over the digestive microbial ecosystem (Hogberg et al., 2005) or directly over the
piglet metabolism (Zhou et al., 1994), by affecting the secretion and activity of pancreatic
and intestinal digestive enzymes or the maintenance of the morphology of the intestinal
mucosa (Li et al., 2001; Hedemann et al., 2006).
Considerable efforts have been made to look for alternatives to antibiotics growth promoters
in animal feeding during the last three decades. Among the most widely used products in
pig and poultry production can be cited the organic acids (Partanen & Mroz, 1999;
Ravindran & Kornegay, 1993), plant extracts (Cowan 1999; Burt 2004), oligosaccharides
(Mull & Perry 2004) or probiotics (Gardiner et al., 2004).
3. Silver as antimicrobial
Silver compounds have been historically used to control microbial proliferation (Wadhera &
Fung, 2005). The antifungal and antibacterial effect of silver nanoparticles, even against
antibiotic-resistant bacteria (Wright et al., 1994; 1999) has been demonstrated in in vitro
conditions. Nowadays, silver compounds are routinely applied in a wide array of industrial
and sanitary fields, such as coating of catheters and surgery material, the production of
synthetic compounds for odontology, treatment of burn injuries, homeopathic medicine or
water purification (Spencer, 1999; Klasen, 2000; Wadhera & Fung, 2005; Atiyeh et al., 2007;
Hwang et al., 2007).
Traditionally, silver has been used as salts (ionic form), mainly nitrate, sulphate or chloride.
However, silver cation is converted into the less effective silver chloride in the stomach or
bloodstream, and can form complexes with various ligands. Silver nitrate is unstable, and can
be toxic to tissues (Atiyeh et al., 2007). In contrast, metallic silver in form of colloidal solution
or as 5 to 100 nm nanoparticles is more stable to hydrochloric acid, is absorbed at a much
lower extent by euchariotic cells and therefore is minimally toxic, and at the same time exert a
higher antimicrobial effect (Choi et al., 2008), which explains why its use has been promoted in
the last decades (Atiyeh et al., 2007). Lok et al. (2006) showed that, even though silver
nanoparticles and silver ions in form of silver nitrate have a similar mechanism of action, their
effective concentrations are at nanomolar and micromolar levels, respectively.
Silver exerts its antimicrobial activity through different mechanisms. It has been reported to
uncouple the respiratory electron transport from oxidative phosphorylation and to inhibit
respiratory chain enzymes (Schreurs & Rosemberg, 1982; Bard & Holt, 2005). Silver also
adheres to bacterial surface, thus altering membrane functions, leading to a dissipation of
the proton motive force (Percival et al., 2005; Lok et al., 2006), and interacts with nucleic acid
bases, inhibiting cell replication (Wright et al., 1994; Yang et al., 2009). Some authors have
demonstrated its toxic effect over different serovars of Escherichia coli (Zhao & Stevens, 1998;
Sondi & Salopek-Sondi, 2004; Jung et al., 2008) and Streptococcus faecalis (Zhao & Stevens,
1998), but its observed effect over Staphylococcus aureus has been variable (Li et al., 2006;
Kim et al., 2007; Jung et al., 2008). Yoon et al. (2007) observed a higher effect of silver
nanoparticles on Bacillus subtilis than on Escherichia coli, suggesting a selective antimicrobial
effect, possibly related to the structure of the bacterial membrane, although Singh et al.
(2008) assume higher sensitivity of Gram-negative bacteria to treatment with nanoparticles.
The possible effects of metallic silver and silver ions over microorganisms from the digestive
tract are scarcely documented. The selective response of silver in such ecosystem, with a

Silver Nanoparticles328
wide diversity of species that can exert either symbiotic (positive) or pathogen (negative)
effects, deserves further attention.
4. Other effects of silver
Despite its potential effect on digestive microbial biodiversity and function, other effects of
metallic silver related with host physiological status, such as the immunological status, the
digestive enzymatic activity and intestinal structure can be expected. This can be assumed
considering the chemical similarity of silver with other metals such as zinc and copper and
the characteristics of their antimicrobial response. The capability of zinc and copper to
minimise the negative effect of weaning on the of height of intestinal villi, thus ensuring its
absorbing potential (Li et al., 2001) and the enhancement of the metabolic pancreatic activity
(Zhou et al., 1994) could also be potentially expected with the use of silver. Besides, studies
related with the role of silver nanoparticles on wound treatment show its role on
metalloproteinases regulation, reducing inflammation and favouring cellular apoptosis and
cicatrisation (Wright et al., 2002; Warriner & Burrell, 2005). Lansdown (2002) indicates that
the topic use of silver promotes an increase of zinc and copper concentration over epithelial
tissue, thus indirectly stimulating its positive effects.
A cytotoxic effect of silver on the host animal must also be considered. This has been
occasionally observed in human medicine when chronic (extended in time) treatments with
high doses of silver have been used, often related with the use of silver compounds for
wound healing or in dental implants (Abe et al., 2003; Lam et al., 2004). Chronic ingestion of
silver compounds may lead to its retention in skin, eyes and other organs such as liver, but
it has been generally considered as a cosmetic problem, with minor or nil pathological
symptoms (Lansdown, 2006). Wadhera & Fung (2005) state that no physiological alterations
or damage of organs of patients with argyria (subcutaneous accumulation of silver
associated with silver salts treatment), even with daily intake of 650 mg ionic silver for 10
months (corresponding to a total of 200 g silver intake). The minimal dose causing
generalised argyria in humans has been fixed in 4 to 5 g (Brandt et al., 2005). According to
Ricketts et al. (1970), the minimal dose of silver nitrate to cause inhibition of cell respiration
in tissues is about 25-fold higher to that inhibits growth of Pseudomonas aeruginosa, and
Gopinath et al. (2008) concluded that a necrotic effect on human cells of silver nanoparticles
occur at concentrations above 44 µg/ml (44 ppm). However, no limiting concentration of
silver intake has been fixed for humans, although the US Environmental Protecting Agency
(EPA) recommends a maximum silver dose in drinking water for chronic or short term (1 to
10 days) intake of 0.05 and 1.14 ppm, respectively (ATSDS 1990).
5. Potential use of silver in animal feeding
In the 50´s, colloidal silver was used as zootechnical additive in poultry diets, but its high
cost at that time avoided its possibility to compete with the lower cost of antibiotics.
Nowadays, the development of industrial processes of silver nanoparticles allows for its
consideration as a potential feed additive, once the banning of the use of antibiotics as
growth promoters. However, the availability of results testing metallic silver nanoparticles
in animal production experiments is very scarce. It has been observed in vitro that the
proportion of coliforms in pigs ileal contents was linearly reduced (P<0.05), whereas no
effect was observed on lactobacilli proportion, when the concentration of colloidal silver in
the medium increased from 0 to 25, 50 or 100 ppm (Fondevila et al., 2009). According to
these results, metallic silver nanoparticles would reduce the viability of organisms with a
potentially harmful effect, such as coliforms, whereas it does not affect lactobacilli, which
positively compete against pathogens proliferation and reduce their virulence (Blomberg et
al., 1993). A trend (P = 0.07) to a coliform reduction in ileal contents was also observed in
vivo by Fondevila et al. (2009) when 20 and 40 ppm of metallic silver nanoparticles were
given to weaned piglets as metallic silver adsorbed in a sepiolite matrix (ARGENTA,
Laboratorios Argenol S.L., Spain) as antimicrobial and growth promoter for weaned pigs
during their transition phase (from 5 to 20 kg weight). Besides, although concentration of
major bacterial groups in the ileum of pigs were not markedly affected, the concentration of
the pathogen Clostridium perfringens/ Cl. histolyticum group was reduced with 20 ppm silver
(P = 0.012). In the same way, Sawosz et al. (2007) did not observed a major effect of colloidal
silver on bacterial concentration in the digestive tract of quails, but only a significant
increase in lactic acid bacteria was observed with 25 ppm.
Results on productive performances in several experiments with pigs and poultry carried
out by our group were variable (Table 1): a numerical increase in daily growth was
generally observed when 20 ppm silver were added compared with the control (no silver),
but this effect was not generally significant. As the productive responses to an additive that
improves the sanitary status of animals are in general inversely proportional to the
environmental quality of the productive site (Cromwell 1995), it is likely that under the
stress conditions of commercial farms the concentration of pathogenic bacteria increased
and thus the effect of silver would be more manifested. In the same way, a lack of effect of
adding zinc oxide had also been sometimes reported (Jensen-Waern et al., 1998; Broom et al.,
2006), which would partly explain this lack of significant results. Studies in animals as
models for humans have shown that high silver concentrations (between 95 and 300 ppm,
corresponding to 2.4 and 7.5-fold the concentrations used in these experiments) in form of
silver salts and given as chronic dose (for more than 18 weeks) reduce weight of mice
(Rungby & Danscher 1984) and turkeys (Jensen et al., 1974). However, these dosing
conditions are considered of much higher toxic potential than low concentration metallic
silver given for short periods of time (Wadhera & Fung 2005). In an experiment (E. Gonzalo,
M.A. Latorre & M. Fondevila, unpublished) where pigs were given 0, 20 and 40 ppm silver
from weaning to slaughter weight (91 kg), the feed to gain ratio (amount of feed per unit of
increased weight) was reduced (P= 0.03) by silver addition, indicating a higher growth
efficiency and showing a reduction in overall production cost.
Another important aspect to verify when an additive is promoted to use is to what extent it
does not challenge the health of the potential consumer. Inclusion of 2500 to 3000 ppm zinc
in diets for post-weaning pig leads to tissue retention from 220 µg/g (Jensen-Waern et al.,
1998; Carlson et al., 1999) to 445 µg/g (Zhang & Guo, 2007) in liver, and retentions up to
3020 µg/g have been reported (Case and Carlson, 2002). In a study carried out with metallic
silver, no silver retention was detected in renal or muscular (semimembranous) tissue in
weaned piglets given 20 or 40 ppm silver for 35 days (n=18), and only 0.435 and 0.837 µg per
g were recorded in liver (Fondevila et al., 2009). Another experiment repeated in the same
conditions (Gonzalo, Latorre & Fondevila, unpublished) showed minimal silver retention in
muscles (0.036 and 0.033 µg/g with 20 and 40 ppm silver in diet) and kidney (0.034 and
0.039 µg/g, respectively) that was observed in 6 out of 8 animals, whereas silver was

Potential use of silver nanoparticles as an additive in animal feeding 329
wide diversity of species that can exert either symbiotic (positive) or pathogen (negative)
effects, deserves further attention.
4. Other effects of silver
Despite its potential effect on digestive microbial biodiversity and function, other effects of
metallic silver related with host physiological status, such as the immunological status, the
digestive enzymatic activity and intestinal structure can be expected. This can be assumed
considering the chemical similarity of silver with other metals such as zinc and copper and
the characteristics of their antimicrobial response. The capability of zinc and copper to
minimise the negative effect of weaning on the of height of intestinal villi, thus ensuring its
absorbing potential (Li et al., 2001) and the enhancement of the metabolic pancreatic activity
(Zhou et al., 1994) could also be potentially expected with the use of silver. Besides, studies
related with the role of silver nanoparticles on wound treatment show its role on
metalloproteinases regulation, reducing inflammation and favouring cellular apoptosis and
cicatrisation (Wright et al., 2002; Warriner & Burrell, 2005). Lansdown (2002) indicates that
the topic use of silver promotes an increase of zinc and copper concentration over epithelial
tissue, thus indirectly stimulating its positive effects.
A cytotoxic effect of silver on the host animal must also be considered. This has been
occasionally observed in human medicine when chronic (extended in time) treatments with
high doses of silver have been used, often related with the use of silver compounds for
wound healing or in dental implants (Abe et al., 2003; Lam et al., 2004). Chronic ingestion of
silver compounds may lead to its retention in skin, eyes and other organs such as liver, but
it has been generally considered as a cosmetic problem, with minor or nil pathological
symptoms (Lansdown, 2006). Wadhera & Fung (2005) state that no physiological alterations
or damage of organs of patients with argyria (subcutaneous accumulation of silver
associated with silver salts treatment), even with daily intake of 650 mg ionic silver for 10
months (corresponding to a total of 200 g silver intake). The minimal dose causing
generalised argyria in humans has been fixed in 4 to 5 g (Brandt et al., 2005). According to
Ricketts et al. (1970), the minimal dose of silver nitrate to cause inhibition of cell respiration
in tissues is about 25-fold higher to that inhibits growth of Pseudomonas aeruginosa, and
Gopinath et al. (2008) concluded that a necrotic effect on human cells of silver nanoparticles
occur at concentrations above 44 µg/ml (44 ppm). However, no limiting concentration of
silver intake has been fixed for humans, although the US Environmental Protecting Agency
(EPA) recommends a maximum silver dose in drinking water for chronic or short term (1 to
10 days) intake of 0.05 and 1.14 ppm, respectively (ATSDS 1990).
5. Potential use of silver in animal feeding
In the 50´s, colloidal silver was used as zootechnical additive in poultry diets, but its high
cost at that time avoided its possibility to compete with the lower cost of antibiotics.
Nowadays, the development of industrial processes of silver nanoparticles allows for its
consideration as a potential feed additive, once the banning of the use of antibiotics as
growth promoters. However, the availability of results testing metallic silver nanoparticles
in animal production experiments is very scarce. It has been observed in vitro that the
proportion of coliforms in pigs ileal contents was linearly reduced (P<0.05), whereas no
effect was observed on lactobacilli proportion, when the concentration of colloidal silver in
the medium increased from 0 to 25, 50 or 100 ppm (Fondevila et al., 2009). According to
these results, metallic silver nanoparticles would reduce the viability of organisms with a
potentially harmful effect, such as coliforms, whereas it does not affect lactobacilli, which
positively compete against pathogens proliferation and reduce their virulence (Blomberg et
al., 1993). A trend (P = 0.07) to a coliform reduction in ileal contents was also observed in
vivo by Fondevila et al. (2009) when 20 and 40 ppm of metallic silver nanoparticles were
given to weaned piglets as metallic silver adsorbed in a sepiolite matrix (ARGENTA,
Laboratorios Argenol S.L., Spain) as antimicrobial and growth promoter for weaned pigs
during their transition phase (from 5 to 20 kg weight). Besides, although concentration of
major bacterial groups in the ileum of pigs were not markedly affected, the concentration of
the pathogen Clostridium perfringens/ Cl. histolyticum group was reduced with 20 ppm silver
(P = 0.012). In the same way, Sawosz et al. (2007) did not observed a major effect of colloidal
silver on bacterial concentration in the digestive tract of quails, but only a significant
increase in lactic acid bacteria was observed with 25 ppm.
Results on productive performances in several experiments with pigs and poultry carried
out by our group were variable (Table 1): a numerical increase in daily growth was
generally observed when 20 ppm silver were added compared with the control (no silver),
but this effect was not generally significant. As the productive responses to an additive that
improves the sanitary status of animals are in general inversely proportional to the
environmental quality of the productive site (Cromwell 1995), it is likely that under the
stress conditions of commercial farms the concentration of pathogenic bacteria increased
and thus the effect of silver would be more manifested. In the same way, a lack of effect of
adding zinc oxide had also been sometimes reported (Jensen-Waern et al., 1998; Broom et al.,
2006), which would partly explain this lack of significant results. Studies in animals as
models for humans have shown that high silver concentrations (between 95 and 300 ppm,
corresponding to 2.4 and 7.5-fold the concentrations used in these experiments) in form of
silver salts and given as chronic dose (for more than 18 weeks) reduce weight of mice
(Rungby & Danscher 1984) and turkeys (Jensen et al., 1974). However, these dosing
conditions are considered of much higher toxic potential than low concentration metallic
silver given for short periods of time (Wadhera & Fung 2005). In an experiment (E. Gonzalo,
M.A. Latorre & M. Fondevila, unpublished) where pigs were given 0, 20 and 40 ppm silver
from weaning to slaughter weight (91 kg), the feed to gain ratio (amount of feed per unit of
increased weight) was reduced (P= 0.03) by silver addition, indicating a higher growth
efficiency and showing a reduction in overall production cost.
Another important aspect to verify when an additive is promoted to use is to what extent it
does not challenge the health of the potential consumer. Inclusion of 2500 to 3000 ppm zinc
in diets for post-weaning pig leads to tissue retention from 220 µg/g (Jensen-Waern et al.,
1998; Carlson et al., 1999) to 445 µg/g (Zhang & Guo, 2007) in liver, and retentions up to
3020 µg/g have been reported (Case and Carlson, 2002). In a study carried out with metallic
silver, no silver retention was detected in renal or muscular (semimembranous) tissue in
weaned piglets given 20 or 40 ppm silver for 35 days (n=18), and only 0.435 and 0.837 µg per
g were recorded in liver (Fondevila et al., 2009). Another experiment repeated in the same
conditions (Gonzalo, Latorre & Fondevila, unpublished) showed minimal silver retention in
muscles (0.036 and 0.033 µg/g with 20 and 40 ppm silver in diet) and kidney (0.034 and
0.039 µg/g, respectively) that was observed in 6 out of 8 animals, whereas silver was

Silver Nanoparticles330
detected in liver of all animals at 0.400 and 0.557 µg/g for 20 and 40 ppm, respectively. It has
to be considered that these concentrations are more than 3000-fold lower than in the case of
zinc and the range is below the EPA recommendation, as it has been commented above.
Further, pigs are not given silver additive during their growth and finishing phases (from 20
to 90-100 kg, commercial slaughter weight), and our group did not detect any traces of silver
in muscles, kidneys or liver of 90 kg pigs receiving the additive up to 20 kg weight, thus
showing the detoxifying capacity of liver to excrete silver (Lansdown, 2006).
In an experiment with broiler chicks as another animal productive species, dosage of
metallic silver nanoparticles (ARGENTA) for 5 weeks was continued by 7 days of non-
supplemented period (Prieto & Fondevila, unpublished). Silver retention was 0.035, 0.031
and 0.045 µg/g in muscular tissue and 0.113, 0.086 and 0.185 µg/g for the same treatments
in liver tissue for 20, 30 and 40 silver ppm in diet, respectively (n=10). Only 5 out of 10
animals given 20 and 30 ppm silver showed detectable concentration in muscles, while 6
and 7 out of 10 animals with the same treatments showed silver concentration in the liver.
Experimental conditions Ag dose
(mg/kg)
Intake
(g/d)
Growth
(g/d)
F:G
(kg/kg) Reference
weaned pigs, n=5, 28 to
35 d age
0
20
40
s.e.m.
162
143
177
--
107
122
157
41.3
Fondevila et al.
(2009)
weaned pigs, n=5, 35 to
42 d
0
20
40
s.e.m.
253
313
365
--
314b
393ab
461 a
36.4
Fondevila et al.
(2009)
weaned pigs, n=6 pens
of 4 pigs, 21 to 35 d
0
20
40
s.e.m.
154b
189a
148 b
8.5
66
102
93
11.0
2.13
1.95
1.70
0.196
Fondevila et al.
(2009)
weaned pigs, n=6 pens
of 4 pigs, 35 to 56 d
0
20
40
s.e.m.
527b
670a
630a
32.3
337
375
347
21.2
1.56b
1.80a
1.82a
0.050
Fondevila et al.
(2009)
weaned pigs, n=6 pens
of 2 pigs, 21 to 147 d;
silver was dosed from
21 to 56 d of age
0
20
40
s.e.m.
1737
1638
1734
46.9
684
677
693
16.8
2.53a
2.42b
2.50ab
0.029
Gonzalo, Latorre
& Fondevila
(unpublished)
broilers, n=8 pens of 28
chicks, 1 to 42 d; silver
was dosed from 1 to 35
d of age
0
20
30
40
s.e.m.
99.7
97.3
96.6
99.0
0.74
54.6
55.3
53.9
54.1
1.28
1.83
1.76
1.79
1.83
0.030
Prieto &
Fondevila
(unpublished)
Table 1. Effect of inclusion of metallic silver nanoparticles (ARGENTA) on productive
performances of animals
F:G, feed to gain ratio, a,b, letters show differences among means (P<0.05)
6. Acknowledgements
Research included in this work has been funded by Laboratorios Argenol, S.L. (Zaragoza,
Spain), through the projects OTRI 2006/0279, OTRI 2007/0640 and DEX-600100-2008-23. J.
Ducha (University of Zaragoza), M.A. Latorre (Centro de Investigación y Tecnología de
Aragón), J. Prieto and E. Gonzalo have been involved in the experimental research included
in this paper.
7. References
Abe, Y.; Ueshige, M.; Takeuchi, M.; Ishii, M. & Akagawa, Y. (2003). Cytotoxicity of
antimicrobial tissue conditioners containing silver-zeolite. International Journal of
Prosthodontology, 16, 141-144.
Agency for Toxic Substances and Diseases Registry (1990). Toxicological profile for silver.
U.S. Public Health Service, 145 pp.
Atiyeh, B.S.; Costagliola, M.; Hayek, S.N. & Dibo, S.A. (2007). Effect of silver on burn wound
infection control and healing: review of the literature. Burns, 33, 139-148.
Bard, A.J. & Holt, K.B. (2005). Interaction of silver ions (I) with the respiratory chain of
Escherichia coli: an electrochemical and scanning electrochemical study of the
antimicrobial mechanism of micromolar Ag+. Biochemistry, 44, 13214-13223.
Blomberg, L.; Henrikson, A. & Conway, P. L. ( 1993). Inhibition of adhesion of Escherichia coli
K88 to piglet ileal mucus by Lactobacillus spp. Applied and Environmental
Microbiology, 59, 34–39.
Brandt, D.; Park, B.; Hoang, M. & Jacobe, H.T. (2005). Argyria secondary to ingestion of
homemade silver solution. Journal of American Academy of Dermatology, 53, S105-
S107.
Broom, L.J.; Miller, H.M.; Kerr, K.G. & Knapp, J.S. (2006). Effects of zinc oxide and
Enterococcus faecium SF68 dietary supplementation on the performance, intestinal
microbiota and immune status of weaned piglets. Research in Veterinary Science, 80,
45-54.
Burt, S. (2004). Essential oils: their antibacterial properties and potential applications in
foods: a review. International Journal of Food Microbiology, 942, 223-253.
Carlson, M.S.; Hill, G.M. & Link, J.E. (1999). Early- and traditionally weaned nursery pigs
benefit from phase-feeding pharmacological concentrations of zinc oxide: effect on
methallothionein and mineral concentrations. Journal of Animal Science, 77, 1199-
1207.
Case, C.L. & Carlson, M.S. (2002). Effect of feeding organic and inorganic sources of
additional zinc on growth performance and zinc balance in nursery pigs. Journal of
Animal Science, 80, 1917-1924.
Choi, O.; Deng, K.K.; Kim, N.J., Ross, L.Jr.; Surampalli, R.Y. & Hu, Z. (2008). The inhibitory
effects of silver nanoparticles, silver ions and silver chloride colloids on microbial
growth. Water Research, 42, 3066-3074.
Cowan, M.M. (1999). Plant products as antimicrobial agents. Clinical Microbiology Reviews 12,
564-582.
Cromwell, G.L. (1991). Antimicriobial agents. In: Swine nutrition, E.R. Miller, D.E. Ullrey, A.J.
Lewis (Eds.), pp. 297-315, CRC Press, Boca Raton.

Potential use of silver nanoparticles as an additive in animal feeding 331
detected in liver of all animals at 0.400 and 0.557 µg/g for 20 and 40 ppm, respectively. It has
to be considered that these concentrations are more than 3000-fold lower than in the case of
zinc and the range is below the EPA recommendation, as it has been commented above.
Further, pigs are not given silver additive during their growth and finishing phases (from 20
to 90-100 kg, commercial slaughter weight), and our group did not detect any traces of silver
in muscles, kidneys or liver of 90 kg pigs receiving the additive up to 20 kg weight, thus
showing the detoxifying capacity of liver to excrete silver (Lansdown, 2006).
In an experiment with broiler chicks as another animal productive species, dosage of
metallic silver nanoparticles (ARGENTA) for 5 weeks was continued by 7 days of non-
supplemented period (Prieto & Fondevila, unpublished). Silver retention was 0.035, 0.031
and 0.045 µg/g in muscular tissue and 0.113, 0.086 and 0.185 µg/g for the same treatments
in liver tissue for 20, 30 and 40 silver ppm in diet, respectively (n=10). Only 5 out of 10
animals given 20 and 30 ppm silver showed detectable concentration in muscles, while 6
and 7 out of 10 animals with the same treatments showed silver concentration in the liver.
Experimental conditions Ag dose
(mg/kg)
Intake
(g/d)
Growth
(g/d)
F:G
(kg/kg) Reference
weaned pigs, n=5, 28 to
35 d age
0
20
40
s.e.m.
162
143
177
--
107
122
157
41.3
Fondevila et al.
(2009)
weaned pigs, n=5, 35 to
42 d
0
20
40
s.e.m.
253
313
365
--
314b
393ab
461 a
36.4
Fondevila et al.
(2009)
weaned pigs, n=6 pens
of 4 pigs, 21 to 35 d
0
20
40
s.e.m.
154b
189a
148 b
8.5
66
102
93
11.0
2.13
1.95
1.70
0.196
Fondevila et al.
(2009)
weaned pigs, n=6 pens
of 4 pigs, 35 to 56 d
0
20
40
s.e.m.
527b
670a
630a
32.3
337
375
347
21.2
1.56b
1.80a
1.82a
0.050
Fondevila et al.
(2009)
weaned pigs, n=6 pens
of 2 pigs, 21 to 147 d;
silver was dosed from
21 to 56 d of age
0
20
40
s.e.m.
1737
1638
1734
46.9
684
677
693
16.8
2.53a
2.42b
2.50ab
0.029
Gonzalo, Latorre
& Fondevila
(unpublished)
broilers, n=8 pens of 28
chicks, 1 to 42 d; silver
was dosed from 1 to 35
d of age
0
20
30
40
s.e.m.
99.7
97.3
96.6
99.0
0.74
54.6
55.3
53.9
54.1
1.28
1.83
1.76
1.79
1.83
0.030
Prieto &
Fondevila
(unpublished)
Table 1. Effect of inclusion of metallic silver nanoparticles (ARGENTA) on productive
performances of animals
F:G, feed to gain ratio, a,b, letters show differences among means (P<0.05)
6. Acknowledgements
Research included in this work has been funded by Laboratorios Argenol, S.L. (Zaragoza,
Spain), through the projects OTRI 2006/0279, OTRI 2007/0640 and DEX-600100-2008-23. J.
Ducha (University of Zaragoza), M.A. Latorre (Centro de Investigación y Tecnología de
Aragón), J. Prieto and E. Gonzalo have been involved in the experimental research included
in this paper.
7. References
Abe, Y.; Ueshige, M.; Takeuchi, M.; Ishii, M. & Akagawa, Y. (2003). Cytotoxicity of
antimicrobial tissue conditioners containing silver-zeolite. International Journal of
Prosthodontology, 16, 141-144.
Agency for Toxic Substances and Diseases Registry (1990). Toxicological profile for silver.
U.S. Public Health Service, 145 pp.
Atiyeh, B.S.; Costagliola, M.; Hayek, S.N. & Dibo, S.A. (2007). Effect of silver on burn wound
infection control and healing: review of the literature. Burns, 33, 139-148.
Bard, A.J. & Holt, K.B. (2005). Interaction of silver ions (I) with the respiratory chain of
Escherichia coli: an electrochemical and scanning electrochemical study of the
antimicrobial mechanism of micromolar Ag+. Biochemistry, 44, 13214-13223.
Blomberg, L.; Henrikson, A. & Conway, P. L. ( 1993). Inhibition of adhesion of Escherichia coli
K88 to piglet ileal mucus by Lactobacillus spp. Applied and Environmental
Microbiology, 59, 34–39.
Brandt, D.; Park, B.; Hoang, M. & Jacobe, H.T. (2005). Argyria secondary to ingestion of
homemade silver solution. Journal of American Academy of Dermatology, 53, S105-
S107.
Broom, L.J.; Miller, H.M.; Kerr, K.G. & Knapp, J.S. (2006). Effects of zinc oxide and
Enterococcus faecium SF68 dietary supplementation on the performance, intestinal
microbiota and immune status of weaned piglets. Research in Veterinary Science, 80,
45-54.
Burt, S. (2004). Essential oils: their antibacterial properties and potential applications in
foods: a review. International Journal of Food Microbiology, 942, 223-253.
Carlson, M.S.; Hill, G.M. & Link, J.E. (1999). Early- and traditionally weaned nursery pigs
benefit from phase-feeding pharmacological concentrations of zinc oxide: effect on
methallothionein and mineral concentrations. Journal of Animal Science, 77, 1199-
1207.
Case, C.L. & Carlson, M.S. (2002). Effect of feeding organic and inorganic sources of
additional zinc on growth performance and zinc balance in nursery pigs. Journal of
Animal Science, 80, 1917-1924.
Choi, O.; Deng, K.K.; Kim, N.J., Ross, L.Jr.; Surampalli, R.Y. & Hu, Z. (2008). The inhibitory
effects of silver nanoparticles, silver ions and silver chloride colloids on microbial
growth. Water Research, 42, 3066-3074.
Cowan, M.M. (1999). Plant products as antimicrobial agents. Clinical Microbiology Reviews 12,
564-582.
Cromwell, G.L. (1991). Antimicriobial agents. In: Swine nutrition, E.R. Miller, D.E. Ullrey, A.J.
Lewis (Eds.), pp. 297-315, CRC Press, Boca Raton.

Silver Nanoparticles332
Fondevila, M.; Herrer, R.; Casallas, M.C.; Abecia, L. & Ducha, J.J. (2009). Silver nanoparticles
as a potential antimicrobial additive for weaned pigs. Animal Feed Science and
Technology, 150, 259-269.
Gardiner, G.E.; Casey, P.G.; Casey, G.; Lynch, P.B.; Lawlor, P.G.; Hill, C.; Fitzgerald, G.F.;
Stanton, C. & Ross, R.P. (2004). Relative ability of orally administered Lactobacillus
murinus to predominate and persist in the porcine gastrointestinal tract. Applied and
Environmental Microbiology, 70, 1895–1906.
Gopinath, P.; Gogoi, S.K.; Chattopadhyay, A. & Gosh, S.S. (2008). Implications of silver
nanoparticle induced cell apoptosis for in vitro gene therapy. Journal of
Nanobiotechnology, 19, 075104.
Hahn, J.D. & Baker, D.H. (1993). Growth and plasma zinc responses of young pigs fed
pharmacologic levels of zinc. Journal of Animal Science, 71, 3020-3024.
Hedemann, M.S.; Jensen, B.B. & Poulsen, H.D. (2006). Influence of dietary zinc and copper
on digestive enzyme activity and intestinal morphology in weaned pigs. Journal of
Animal Science, 84, 3310-3320.
Hill, G.M.; Cromwell, G.L.; Crenshaw, T.D.; Dove, C.R.; Ewan, R.C.; Knabe, D.A.; Lewis,
A.J.; Libal, G.W.; Mahan, D.C.; Shurson, G.C.; Southern, L.L. & Veum, T.L. (2000).
Growth promotion effects and plasma changes from feeding high dietary
concentrations of zinc and copper to weanling pigs (regional study). Journal of
Animal Science, 78, 1010-1016.
Hogberg, O.; Canibe, N.; Poulsen, H.D.; Hedemann, M.S. & Jensen, B.B. (2005). Influence of
dietary zinc oxide and copper sulphate on the gastrointestinal ecosystem in newly
weaned piglets. Applied and Environmental Microbiology, 71, 2267-2277.
Hwang, M.G. ; Katayama, H. & Ohgaki, S. (2007). Inactivation of Legionella pneumophila and
Pseudomonas aeruginosa: evaluation of the bactericidal ability of silver cations. Water
Research, 41, 4097-4104.
Jensen, LS; Peterson, RP & Falen, L. (1974). Inducement of enlarged hearts and muscular
dystrophy in turkey poults with dietary silver. Poultry Science, 53, 57-64.
Jensen-Waern, M.; Melin, L.; Lindberg, R.; Johanisson, A.; Peterson, L. & Wallgren, P. (1998).
Dietary zinc oxide in weaned pigs-effects on performance, tissue concentrations,
morphology, meutrophil functions and faecal microflora. Research in Veterinary
Science, 64, 225-231.
Jung, W.K.; Koo, H.K.; Kim, K.W.; Shin, S.; Kim, S.H. & Park, Y.H. (2008). Antibacterial
activity and mechanism of action of the silver ion in Staphylococcus aureus and
Escherichia coli. Applied and Environmental Microbiology, 74, 2171-2178.
Kim, J.S.; Kuk, E.; Yu, K.N.; Kim, J.H.; Park, S.J.; Lee, H.J.; Kim, S.H.; Park, Y.K.; Park, Y.H.;
Hwang, C.Y.; Kim, Y.K.; Lee, Y.S.; Jeong, D.H. & Cho, M.H. (2007). Antimicrobial
effect of silver nanoparticles. Nanomedicine: Nanotecnology, Biology and Medicine, 3,
95-101.
Klasen, H.J. (2000). Historical review of the use of silver in the treatment of burns. I. Early
uses. Burns, 26, 117-130
Lam, P.K.; Chan, E.S.; Ho, W.S. & Liew, C.T. (2004). In vitro cytotoxicity testing of
nanocrystalline silver dressing (Acticoat) on cultured keratinocytes. British Journal
of Biomedical Science, 61, 125-127.
Lansdown, A.B. (2006). Silver in health care: antimicrobial effects and safety in use. Current
Problems in Dermatology, 33, 17-34.
Li, B. T.; Van Kessel, A. G.; Caine, W. R.; Huang, S. X. & Kirkwood, R. N. (2001). Small
intestinal morphology and bacterial populations in ileal digesta and feces of newly
weaned pigs receiving a high dietary level of zinc oxide. Canadian Journal of Animal
Science, 81, 511-516.
Li, Y.; Leung, P.; Yao, L.; Song, K.W. & Newton, E. (2006). Antimicrobial effect of surgical
masks coated with nanoparticles. Journal of Hospital Infection, 62, 58-63
Lok, C.N.; Ho, C.M.; Chen, R.; He, Q.Y.; Yu, W.Y.; Sun, H.; Tam, P.K.H.; Chiu, J.F. & Che,
C.M. (2006). Proteomic analysis of the mode of antibacterial action of silver
nanoparticles. Journal of Proteome Research, 5, 916-924.
Mull, A.J. & Perry, F.G. (2001). The role of fructo-oligosaccharides in animal nutrition. In
Recent developments in pig nutrition 3, J. Wiseman y P.C. Garnsworthy (eds.), pp. 79-
105, Nottingham University Press, Nottingham.
Partanen, K.H. & Mroz, Z. (1999) Organic acids for performance enhancement in pig diets.
Nutrition Research Reviews, 12, 117-145.
Percival, S.L.; Bowler, P.G. & Russell, D. (2005). Bacterial resistance to silver in wound care.
Journal of Hospital Infection, 60, 1-7.
Ravindran, V., Kornegay, E.T.,1993. Acidification of weaner pig diets: a review. Journal of
the Science of Food and Agriculture 62, 313-322.
Ricketts, C.R.; Lowbury, E.J.L.; Lawrence, J.C.; Hall, M. & Wilkins, M.D. (1970). Mechanism
of prophylaxis by silver compounds against infection of burns. British Medical
Journal, 2, 444-446.
Rungby, J. & Danscher, G. (1984). Hypoactivity in silver exposed mice. Acta Pharmacologica
Toxicologica, 55, 398-401.
Sawosz, E.; Binek, M.; Grodzik, M.; Zielinska, M.; Sysa, P.; Szmidt, M.; Niemec, T. &
Chwalibog, A. (2007). Influence of hydrocolloidal silver nanoparticles on
gastrointestinal microflora and morphology of enterocytes of quails. Archives of
Animal Nutrition, 61, 444-451.
Schreurs, W.J. & Rosenberg, H. (1982). Effect of silver ions on transport and retention of
phosphate by Escherichia coli. Journal of Bacteriology, 152, 7-13.
Singh, M.; Singh, S., Prasad, S. & Gambhir, I.S. (2008). Nanotechnology in medicine and
antibacterial effect of silver nanoparticles. Digest Journal in Nanomaterials and
Biostructures, 3, 115-122.
Smith, J.W.; Tokach, M.D.; Goodband, R.D.; Nelssen, J.L. & Richert, B.T. (1997). Effects of the
interrelationship between zinc oxide and copper sulfate on growth performance of
early-weaned pigs. Journal of Animal Science, 75, 1861-1866.
Sondi, I. & Salopek-Sondi, B. (2004). Silver nanoparticles as antimicrobial agent : a case study
on E. coli as a model for Gram-negative bacteria. Journal of Colloid Interface Science,
275, 177-182.
Spencer, R.C. (1999). Novel methods for the prevention of infection of intravascular devices.
Journal of Hospital Infection, 43, S127-S135.
Wadhera, A. & Fung, M. (2005). Systemic argyria associated with ingestion of colloidal
silver. Dermatology Online Journal 11, 12 (http://dermatology.cdlib.org/111).
Warriner, R. & Burrell, R.E. (2005). Infection and the chronic wound: a focus on silver.
Advances on Skin Wound Care, 18, 2-12.

Potential use of silver nanoparticles as an additive in animal feeding 333
Fondevila, M.; Herrer, R.; Casallas, M.C.; Abecia, L. & Ducha, J.J. (2009). Silver nanoparticles
as a potential antimicrobial additive for weaned pigs. Animal Feed Science and
Technology, 150, 259-269.
Gardiner, G.E.; Casey, P.G.; Casey, G.; Lynch, P.B.; Lawlor, P.G.; Hill, C.; Fitzgerald, G.F.;
Stanton, C. & Ross, R.P. (2004). Relative ability of orally administered Lactobacillus
murinus to predominate and persist in the porcine gastrointestinal tract. Applied and
Environmental Microbiology, 70, 1895–1906.
Gopinath, P.; Gogoi, S.K.; Chattopadhyay, A. & Gosh, S.S. (2008). Implications of silver
nanoparticle induced cell apoptosis for in vitro gene therapy. Journal of
Nanobiotechnology, 19, 075104.
Hahn, J.D. & Baker, D.H. (1993). Growth and plasma zinc responses of young pigs fed
pharmacologic levels of zinc. Journal of Animal Science, 71, 3020-3024.
Hedemann, M.S.; Jensen, B.B. & Poulsen, H.D. (2006). Influence of dietary zinc and copper
on digestive enzyme activity and intestinal morphology in weaned pigs. Journal of
Animal Science, 84, 3310-3320.
Hill, G.M.; Cromwell, G.L.; Crenshaw, T.D.; Dove, C.R.; Ewan, R.C.; Knabe, D.A.; Lewis,
A.J.; Libal, G.W.; Mahan, D.C.; Shurson, G.C.; Southern, L.L. & Veum, T.L. (2000).
Growth promotion effects and plasma changes from feeding high dietary
concentrations of zinc and copper to weanling pigs (regional study). Journal of
Animal Science, 78, 1010-1016.
Hogberg, O.; Canibe, N.; Poulsen, H.D.; Hedemann, M.S. & Jensen, B.B. (2005). Influence of
dietary zinc oxide and copper sulphate on the gastrointestinal ecosystem in newly
weaned piglets. Applied and Environmental Microbiology, 71, 2267-2277.
Hwang, M.G. ; Katayama, H. & Ohgaki, S. (2007). Inactivation of Legionella pneumophila and
Pseudomonas aeruginosa: evaluation of the bactericidal ability of silver cations. Water
Research, 41, 4097-4104.
Jensen, LS; Peterson, RP & Falen, L. (1974). Inducement of enlarged hearts and muscular
dystrophy in turkey poults with dietary silver. Poultry Science, 53, 57-64.
Jensen-Waern, M.; Melin, L.; Lindberg, R.; Johanisson, A.; Peterson, L. & Wallgren, P. (1998).
Dietary zinc oxide in weaned pigs-effects on performance, tissue concentrations,
morphology, meutrophil functions and faecal microflora. Research in Veterinary
Science, 64, 225-231.
Jung, W.K.; Koo, H.K.; Kim, K.W.; Shin, S.; Kim, S.H. & Park, Y.H. (2008). Antibacterial
activity and mechanism of action of the silver ion in Staphylococcus aureus and
Escherichia coli. Applied and Environmental Microbiology, 74, 2171-2178.
Kim, J.S.; Kuk, E.; Yu, K.N.; Kim, J.H.; Park, S.J.; Lee, H.J.; Kim, S.H.; Park, Y.K.; Park, Y.H.;
Hwang, C.Y.; Kim, Y.K.; Lee, Y.S.; Jeong, D.H. & Cho, M.H. (2007). Antimicrobial
effect of silver nanoparticles. Nanomedicine: Nanotecnology, Biology and Medicine, 3,
95-101.
Klasen, H.J. (2000). Historical review of the use of silver in the treatment of burns. I. Early
uses. Burns, 26, 117-130
Lam, P.K.; Chan, E.S.; Ho, W.S. & Liew, C.T. (2004). In vitro cytotoxicity testing of
nanocrystalline silver dressing (Acticoat) on cultured keratinocytes. British Journal
of Biomedical Science, 61, 125-127.
Lansdown, A.B. (2006). Silver in health care: antimicrobial effects and safety in use. Current
Problems in Dermatology, 33, 17-34.
Li, B. T.; Van Kessel, A. G.; Caine, W. R.; Huang, S. X. & Kirkwood, R. N. (2001). Small
intestinal morphology and bacterial populations in ileal digesta and feces of newly
weaned pigs receiving a high dietary level of zinc oxide. Canadian Journal of Animal
Science, 81, 511-516.
Li, Y.; Leung, P.; Yao, L.; Song, K.W. & Newton, E. (2006). Antimicrobial effect of surgical
masks coated with nanoparticles. Journal of Hospital Infection, 62, 58-63
Lok, C.N.; Ho, C.M.; Chen, R.; He, Q.Y.; Yu, W.Y.; Sun, H.; Tam, P.K.H.; Chiu, J.F. & Che,
C.M. (2006). Proteomic analysis of the mode of antibacterial action of silver
nanoparticles. Journal of Proteome Research, 5, 916-924.
Mull, A.J. & Perry, F.G. (2001). The role of fructo-oligosaccharides in animal nutrition. In
Recent developments in pig nutrition 3, J. Wiseman y P.C. Garnsworthy (eds.), pp. 79-
105, Nottingham University Press, Nottingham.
Partanen, K.H. & Mroz, Z. (1999) Organic acids for performance enhancement in pig diets.
Nutrition Research Reviews, 12, 117-145.
Percival, S.L.; Bowler, P.G. & Russell, D. (2005). Bacterial resistance to silver in wound care.
Journal of Hospital Infection, 60, 1-7.
Ravindran, V., Kornegay, E.T.,1993. Acidification of weaner pig diets: a review. Journal of
the Science of Food and Agriculture 62, 313-322.
Ricketts, C.R.; Lowbury, E.J.L.; Lawrence, J.C.; Hall, M. & Wilkins, M.D. (1970). Mechanism
of prophylaxis by silver compounds against infection of burns. British Medical
Journal, 2, 444-446.
Rungby, J. & Danscher, G. (1984). Hypoactivity in silver exposed mice. Acta Pharmacologica
Toxicologica, 55, 398-401.
Sawosz, E.; Binek, M.; Grodzik, M.; Zielinska, M.; Sysa, P.; Szmidt, M.; Niemec, T. &
Chwalibog, A. (2007). Influence of hydrocolloidal silver nanoparticles on
gastrointestinal microflora and morphology of enterocytes of quails. Archives of
Animal Nutrition, 61, 444-451.
Schreurs, W.J. & Rosenberg, H. (1982). Effect of silver ions on transport and retention of
phosphate by Escherichia coli. Journal of Bacteriology, 152, 7-13.
Singh, M.; Singh, S., Prasad, S. & Gambhir, I.S. (2008). Nanotechnology in medicine and
antibacterial effect of silver nanoparticles. Digest Journal in Nanomaterials and
Biostructures, 3, 115-122.
Smith, J.W.; Tokach, M.D.; Goodband, R.D.; Nelssen, J.L. & Richert, B.T. (1997). Effects of the
interrelationship between zinc oxide and copper sulfate on growth performance of
early-weaned pigs. Journal of Animal Science, 75, 1861-1866.
Sondi, I. & Salopek-Sondi, B. (2004). Silver nanoparticles as antimicrobial agent : a case study
on E. coli as a model for Gram-negative bacteria. Journal of Colloid Interface Science,
275, 177-182.
Spencer, R.C. (1999). Novel methods for the prevention of infection of intravascular devices.
Journal of Hospital Infection, 43, S127-S135.
Wadhera, A. & Fung, M. (2005). Systemic argyria associated with ingestion of colloidal
silver. Dermatology Online Journal 11, 12 (http://dermatology.cdlib.org/111).
Warriner, R. & Burrell, R.E. (2005). Infection and the chronic wound: a focus on silver.
Advances on Skin Wound Care, 18, 2-12.

Silver Nanoparticles334
Wright, J.B.; Lam, K. & Burrell, R.E. (1994). Wound management in an era of increasing
bacterial antibiotic resistance: a role for topical silver treatment. American Journal of
Infection Control, 26, 572-577.
Wright, J.B.; Lam, K.; Buret, A.G.; Olson, M.E. & Burrell, R.E. (2002). Early healing events in
a porcine model of contaminated wounds: effects of nanocristalline silver on matrix
metalloproteinases, cell apoptosis and healing. Wound Repair Regeneration, 10, 141.
Wright, J.B.; Lam, K.; Hansen, D. & Burrell, R.E. (1999). Efficacy of topical silver against
fungal burn wound pathogens. American Journal of Infection Control, 27, 344-350.
Yang, W.; Shen, C.; Ji, Q.; An, H.; Wang, J.; Liu, Q. & Zhang, Z. (2009). Food storage material
silver nanoparticles interfere with DNA replication fidelity and bind with DNA.
Nanotechnology, 20, 085102 (7 pp).
Yoon, K.Y.; Byeon, J.H.; Park, J.H. & Hwang, J. (2007). Susceptibility constrants of Escherichia
coli and Bacillus subtilis to silver and copper nanoparticles. Science of the Total
Environment, 373, 572-575.
Zhang, B. & Guo Y. (2007). Beneficial effect of tetrabasic zinc chloride for weanling piglets
and the bioavailability of zinc in tetrabasic form relative to ZnO. Animal Feed
Science and Technology, 135, 75-85.
Zhao, G. & Stevens, J.R. (1998). Multiple parameters for the comprehensive evaluation of the
susceptibility of Escherichia coli to the silver ion. Biometals, 11, 27-32.
Zhou, W.; Kornegay, E.T.; Lindemann, M.D.; Swinkels, J.W.G.M.; Welton, M.K. & Wong,
E.A. (1994). Stimulation of growth by intravenous injection of copper in weanling
pigs. Journal of Animal Science, 72, 2395-2403.