Rare earth elements as alternative growth promoters in pig production
Institute for Animal Physiology, Physiological Chemistry and Animal Nutrition,
Ludwig-Maximilians-University Munich, Germany
Institute for Animal Physiology, Physiological Chemistry and Animal Nutrition,
alternative growth promoter _ feed conversion ratio _ in-feed antibiotics _ lanthanides
Growth promoters or performance enhancers are used worldwide in pig production.
For over 50 years, antibiotics as feed additives proved to be effective in a better
utilization of nutrients with an improved feed conversion ratio and better growth rate
in most cases. In the EU, most of these feed antibiotics are forbidden now, and the
last three ones still allowed will be banned at the end of 2005. In China for more than
40 years, special mineral salts called Rare Earth Elements (REE) or lanthanides with
the elements lanthanum, cerium and others are used as feed additives in animal
production. Numerous reports in the Chinese literature describe that a small amount
of these REE mixtures in the diet can increase the body weight gain of pigs, cattle,
sheep and chicken and it is reported that they increase milk and egg production. This
finding was totally unnoticed in the western world. In the past five years about a
dozen of studies -mainly in pigs- were performed under western animal production
conditions. Most of these studies in piglets and in fattening pigs provided significant
data, indicating that REE imported from China can improve weight gain and feed
conversion. Recently, in Switzerland, REE supplemented pig feed was admitted to
the market. The safety of REE, which are ubiquitous at low concentration in all soils
and plants, has been proven. Long term studies – even in man for medical purposes
- showed that REE toxicity is similar to the one of table salt (NaCl). The mechanism
of the action of REE is still debated. It is possible that they develop their activity in the
digestive tract since very little is absorbed. However, it is also discussed that these
lanthanides - or one of them - have the characteristics of essential trace elements for
animals. In summary, REE might be of interest in animal and especially in pig
production as a new, safe and inexpensive alternative growth promoter.
Antibiotics as feed additives have been banned already for some years in Sweden
and in Switzerland. In the European Union, the three last antibiotics, still allowed as
growth promoters, will be phased out at the end of 2005, too. Worldwide there is an
increasing demand for food which can only be achieved by an increased meat
production. The full ban of antibacterial growth promoters might seriously affect post-
weaning health and performance (Lynch, 1999). This will almost certainly necessitate
the development of new feeding and health care strategies. Therefore, there is a
strong need for alternative growth promoters such as pro- and prebiotics, enzymes,
organic acids as well as herb extracts (Wenk, 2003). These feed additives have to be
efficient, safe and they should not harm the environment (Khan, 2004).
A very new approach in this respect is the supplementation of feed with “Rare Earth
Elements” (REE). REE, are the elements scandium, yttrium and the lanthanides from
lanthanum to lutetium. Although the rare earth elements are not particularly rare in
the earth crust, the term persists. In this article, REE refers mainly to the lanthanides
and among them to the elements lanthanum (La, atomic number 57), cerium (Ce,
atomic number 58) and praseodymium (Pr, atomic number 59). Lanthanum and
cerium occur geologically in the earth at a concentration similar to the essential trace
element cobalt and thus are not rare at all (Süss, 2004). Since 80% of the world
reserves on REE are located in China, this country became the main producer and
supplier of REE in form of mineral concentrates, alloys and oxides. The main
application of REE is in metallurgy, chemical industry, electronics and in agriculture
About 25% of the lanthanides produced are used in carbon-arc lighting applications.
Another 25% of the production of lanthanides is used in the form of mixed lanthanide
metals and cerium metal. These metals are used in cigarette lighter flints,
magnesium alloys, and some of the ferrous alloys. The third 25% of lanthanum
production is used in the glass industry. Didymium (a mixture of praseodymium and
neodymium), cerium salts, and some separated lanthanides have important uses in
both the coloring and the decoloring of glass. The remaining 25% of the lanthanide
usage is divided among many miscellaneous applications, including television tubes,
catalysts, lasers and for agricultural uses (Evans, 1990).
In China, REE -usually a mixture of mainly cerium, lanthanum and praseodymium-
have been used already for 40 years as performance enhancers in agricultural plant
production, and quite remarkable results were reported from Chinese agricultural
operations (Wan et al., 1998). Although the reason for these growth promoting and
yield increasing effects is still unknown, it is speculated that a physiological
interaction of REE and calcium might influence the structure and function of
cytoplasma membrane, of photosynthesis or enzyme activity (Hu et al., 2004).
The Chinese data were confirmed in different other countries, e.g. in Australia
(Diatloff et al., 1995) and the United Kingdom (Andrew et al., 1983). REE
supplemented fertilizer may increase productivity by up to 15% (Wen et al., 2000),
but it does not increase the REE content in the products (Xu et al., 2002). In
hydroponic studies Tucher et al (2001) showed that there is a strong effect of
lanthanum in the culture medium on the composition of the minerals in the plant.
In animal production, as with plants, amazing results have been reported in the
Chinese literature, while in the western world there was no knowledge at all of these
growth promoters. According to these numerous publications, a small amount of REE
in the feed can increase the body weight gain of cattle, pigs, chicken, fish and
rabbits, and might increase milk production of dairy cows and egg production of
laying hens (Shen at al., 1991). Feed conversion ratios were also improved in nearly
all animal categories (see table 1).
For pigs and piglets, multiple Chinese articles concerning performance enhancing
effects of REE exist. For example in weaned piglets with a body weight of about 7 kg,
the body weight gain was increased by 5% to 23% and the feed conversion was
improved between 4% and 19% under the influence of REE (He and Xia, 1998). In
piglets with a body weight between 13 and 17 kg, improvements in weight gains of
11% to 20% and of feed conversion ratios of 5% to 9% were reported (Li et al., 1992;
He and Xia 1998). In growing pigs in a body weight range of 30 to 50 kg, REE
caused an increased body weight gain of 9% to 13% and the feed conversion ratios
were improved by 6% to 8% (Cheng et al., 1994) and in a recent paper by Wang and
Xu (2003) a weight gain of 13% and an improved feed conversion ratio of 7% were
In general, no particular REE elements were added to the feed, but varying mixtures
of mainly cerium, lanthanum and praseodymium with traces of the other lanthanides.
Furthermore, the anions of the REE salts are differing. Nitrates and chlorides were
mostly used at the beginning, while organic compounds are used in recent studies.
These include REE citrate, gluconate, or the aminoacids methionine, lysine and
glutamine may be bound. The concentration applied also varies. In pigs, for example
between 100 mg and 600 mg of the REE salts with varying purity were added per kg
of feed, and therefore the data are hardly comparable. Since the literature on the
effects of REE is predominantly written in Chinese, detailed results are scarcely
available to occidental scientists, and the sources are difficult to assess, because
quite often details concerning experimental methods are not given and statistical
treatment of the data was not performed. Thus, important research questions in the
Chinese reports are still open, making a comprehensive understanding of the action
of REE as feed additives rather difficult.
Feeding studies under “western condition”
Since Chinese animal husbandry conditions can hardly be compared with those in
Europe or the United States, and since western conditions with high performance
animal breed and optimised feed may be less suspectable to growth promoters and
performance enhancers, it seemed urgently needed to redo the REE feeding studies
The first in a row of feeding studies (see table 2) in pigs was performed in 1999
(Rambeck et al., 1999). A total of 72 crossbred piglets (Deutsche Landrasse x
Pietrain) with an average body weight of about 7 kg were given different REE salts,
either rather pure lanthanum chloride (99.7% LaCl3x6H20) or a REE mixture of 38.0%
LaCl3x6H20, 52.1% CeCl3x6H20 and 3% PrCl3x6H20. The REE were supplemented at
75 mg/kg and at 150 mg/kg to a complete diet (52.7% barley, 20% wheat, 18.8%
soybean, metabolic energy 13 MJ/kg, digestible crude protein 184 g/kg) which was
given for 5 weeks. The best results were obtained in the REE-mixture. Body weight
gain improved by up to 5%, feed conversion ratio by up to 7% (p<0.05).
In a second study (He et al., 2001) crossbred piglets with 17.5 kg body weight were
given a diet, supplemented with 300 mg REE-mixture per kg. After 1 month the REE
group had a significantly higher body weight gain of 19% and the feed conversion
ratio improved significantly by 11%. After another month of REE supplementing, body
weight gain was still 12% better and feed conversion ratio still 3% better than the
control group (not significant). The health of the animals, the meat quality and the
safety of the animal products were not influenced by REE. The results from
slaughtering and meat quality control showed that according to the quality class
“EUROP” all animals were graded E or U (the two best classes). Also other meat
quality parameters were not affected by REE either pH1 and pH24 as well as the
brightness of the meat and the ratio meat to fat did not differ significantly (Rambeck
et al., 2004). The REE contents in the samples of muscle, liver and kidneys from pigs
in both experimental groups were very low. Although the content of La in the REE
group was higher than that in the control group, generally the accumulation rates in
all the experimental pigs were very low and close to the limit of detection.
In a field study in Switzerland, two trials were performed, one with 97 piglets (11.2 kg
at the beginning), the other with 176 piglets (8.3 kg at the beginning) (Schweizer
Edelschwein). After 16 days, and 30 days of feeding respectively, a 200 mg REE-
mixture per kg body weight gain was higher by 3 to 10% and feed conversion ratio
improved by 2 to 9% as compared to the controls. This was the first time that REE
were shown to be effective under field conditions (Eisele, 2003).
Since it is known that the bioavailability of REE salts is influenced by its anion (Shan
et al., 2002), the effect of REE-citrate was studied. While REE-citrate had shown to
increase significantly body weight gain by 7% in chicken (Halle et al., 2003), REE-
chloride under similar conditions neither influenced weight gain nor feed conversion
(Schuller et al., 2002). Therefore, feeding studies with REE-citrate were initiated in
piglets. This REE salt has the advantage that it is much less hygroscopic than REE-
chloride and therefore much better to handle as a feed additive.
In a feeding study, lasting 6 weeks, 50, 100 and 200 mg of REE-citrate were given to
28 piglets (n=7 per group) weighing 8.6 kg. A dose dependent response in the form
of increased weight gain by up to 22% and feed conversion ratios of up to 19% were
observed in this trial (Knebel, 2004).
Significantly better performance in pigs fed REE-citrate for the whole fattening period
were obtained by Kessler (2004). When REE-citrate was given at a concentration of
250 mg/kg diet, it took control animals 102 days to reach 104 kg body weight, while
REE-citrate supplemented animals needed only 93 days. The average weight gain
per day was 782 g/day vs 851 g/day. Feed conversion ratio improved from 2.5 in the
control to 2.4 in the REE-citrate group. All these differences were significant. What
was especially astonishing and what had not been described before was that the
effect in female animals was roughly twice as high as in male castrated animals (see
It has to be mentioned that feeding studies have also been published where no
improvement of growth and feed conversion was found. In a feeding study with
fatting pigs for example, diets with different REE anions in a concentration of 100 mg
per kg feed showed no growth promoting effects (Halle et al., 2002). But referring to
the Chinese literature, only a distinct concentration of REE in the diet can improve
body weight gain and feed conversion, a low content of REE may have little or even
no effects at all. In another trial, REE chlorides had no effect at all on weight gain and
feed conversion, however in this case the piglets had to be treated first with
antibiotics for diarrhea (Eisele, 2003).
What are the possible explanations for this striking effect of REE in pigs? As REE are
poorly absorbed from the gastrointestinal tract, it was thought that REE influence the
microbial composition in the gut and thus improve digestibility and utilization of
nutrients in the diet (Li et al., 1992). High concentrations of lanthanides are usually
required for inhibition of bacterial growth, while several authors have reported that
low concentrations may stimulate bacterial growth (Muroma, 1958).
Different reasons for the bactericidal action and the bacteriostatic activity of REE are
discussed. Biochemical and histological evidence confirms the binding of lanthanum
to the surface of bacteria. This reduces the surface charge and retards
electrophoretic migration. When the surface charge is completely neutralized,
flocculation occurs (Evans, 1990). Additionally bacterial respiration is strongly
In general, bacteria seem to be more susceptible to lanthanides than fungi, and the
heavier lanthanides tend to be more detrimental than the lighter ones. But
lanthanides also inhibit the formation and germination of fungal spores (Talburt and
However, analysis of the gut flora in chicken revealed that the main microbial
populations of the alimentary canal were unaffected by REE supplementation
(Schuller et al., 2002). In vitro studies in a RUSITEC (Rumen Simulation Technique)
system indicated that ruminal fermentation and ruminal microorganisms were not
Another possibility might be an influence of REE on the activity of certain hormones
and enzymes, like growth hormone or T3. Data from Xu et al. (1999) and He et al.
(2003) point in this direction. In growing rats, lanthanum as well as a mixture of
different REE chlorides had positive effects on body weight gain and improved feed
conversion ratio significantly. Furthermore, supplementation of REE had clear effects
on blood parameters. Some enzymes like alkaline phosphatase and alanine
aminotransferase increased significantly, blood glucose decreased and creatinine in
blood increased. This suggests that even when only a very small amount of REE is
absorbed, this might affect the physiological metabolism in the animal. Studies with
preadipocytes in cell culture indicate that REE stimulate the proliferation of these
cells and influence the concentration of fatty acids, suggesting an effect on
adipogenesis and lipogenesis rates in adipose tissue (He et al., 2004). Because
there is a special relationship between REE and calcium, it was also suggested that
REE may affect activities of hormones or enzymes by replacing or inhibiting calcium
(Hanioka et al., 1994). It might also well be that the lanthanides are essential trace
elements for man and animals, a fact that might be overlooked since they are
ubiquitous, occurring at low concentrations in all kinds of soil and in all plants
(Wyttenbach et al., 1998; Krafka, 1999). Though REE have attributes of essential
trace elements, there is no proof at all yet.
Only very small amounts of REE are absorbed when given orally. Determination of
REE in muscle and in liver and kidney after 3 months of REE feeding to pigs was
performed by neutron activation analyses and by ICP-MS (He et al., 2001). REE
concentration was partially below the limit of detection, and lower than the content of
REE in plants, fruit and vegetables (Krafka, 1999).
Studies on the eventual toxicity of orally given REE are numerous. One of the very
recent ones (Richter, 2003) states that the oral, acute toxicity in animal experiments
is very low with an LD50 of up to 10 g / kg body weight. This toxicity is even lower in
the presence of complexing agents like citrate. Longterm studies from China where
REE are applied to a large extent in fertilizer show that there are no negative effects.
The low oral toxicity of the REE can also be deduced from the fact that its LD50 is the
same as the one of table salt (Wald 1990).
Since the chemical and biochemical behaviour of the different REE are very similar,
the new numerous studies on lanthanum alone for human medicine purposes are
most interesting in this respect. Lanthanum carbonate is a novel treatment for
hyperphosphatemia in dialysis patients. In the course of obtaining the registration for
this new alternative phosphate binder, comprehensive toxicological, pharmacological
and clinical long term studies treatments were performed in man. Up to 3 g of
elemental lanthanum per day and person for up to 4 years were well tolerated, no
adverse and toxic effects occurred and there was no evidence of significant systemic
accumulation (Harrison and Scott, 2004; Hutchison et al., 2004; Locatelli et al., 2004;
From October 2004 on, only that feed additives that passed a renewed European
Food Safety Authority (EFSA) procedure can be put on the market in the EU. Under
these new rules feed additives will be categorised as technological additives,
zootechnical additives and coccidiostats and histomostats (Khan, 2004). The terms
growth promoters or performance enhancers do not occur anymore. If it can be
proven that REE have the character of trace elements, they belong to the nutritional
additives, if they enhance the digestibility or stabilize the gut flora, they are
How costly the procedure of registering feed additives will be, has been described
recently (Pape, 2004), but the market for feed additives is big (in Germany total
turnover of feed additives in 2003 was about 256 million Euro), and especially after
the ban on in-feed antibiotics, it started to move quickly.
In Switzerland, REE obtained a temporary registration under the trade name
“Lancer“”. It can be supplemented like other essential trace elements to the feed of
piglets and pigs at a concentration between 150 and 300 mg REE per kg feed.
Farmers unanimously report a better faeces quality and an increased health status,
however, these are mostly subjective observations (Zehentmayer, 2004).
In conclusion, rare earth elements may well be of interest in animal - and especially
in pig production as a new, safe and inexpensive alternative feed additive.
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Table 2: Chinese feeding studies with Rare Earth Elements
REE dosage References
WG = weight gainFC = feed conversionEY = egg yieldEW = egg weight
Table 2: Feeding studies with Rare Earth Elements under „western conditions“
REE dosage References
Figure 1: Feed conversion ratio of female and male pigs during the feeding study of
Figure 2: Daily body weight gain of female and male pigs during the feeding study of
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