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Abstract

Due to selenium deficiencies commonly occurring in Europe, horse breeders must supplement the animals' diet with this element. However, it is essential to know the level of selenium in the feed and in the animal tissues. The aim of the study was to determine and compare the serum content of selenium in horses in relation to the feeding season. The horses were used for recreation and sport. Blood was collected from the jugular vein into sterile test tubes without coagulant. In the mares that did not receive selenium supplements, a very low serum level of selenium was observed. The values were far below the norms established for horses (100 µg/l-200 µg/l) and ranged from 20 µg/l to 38 µg/l. The level of selenium in the mares which received pure selenium or selenium in the form of mineral preparations ranged from 56 µg/l to 85 µg/l. However, this level is still below the reference values. The geldings that received selenium, mineral and vitamin supplements and special feed had an appropriate level of selenium in the blood. The horses that did not receive selenium as a supplement had a low level of selenium, well below the norm.
Wyganowska et al., The J. Anim. Plant Sci. 27(5):2017
1448
THE EFFECT OF SELENIUM ON PROPER BODY FUNCTION IN HORSES
A. Wyganowska1, K. Górski2, B. Jania1,3, A. Danielewicz1and K. Andraszek1,*
1Department of Animal Genetics and Horse Breeding, 2Department of Reproduction and Animal Hygiene, Institute of
Bioengineering and Animal Breeding, Siedlce University of Natural Sciences and Humanities, 14 Prusa Str, 08-110
Siedlce, Poland, 3Veterinary Diagnostic Laboratory LAB-WET, Wita Stwosza 30, 02-661 Warszawa, Poland
*Corresponding author’s. e-mail: andrasz@uph.edu.pl
ABSTRACT
Due to selenium deficiencies commonly occurring in Europe, horse breeders must supplement the animals’ diet with this
element. However, it is essential to know the level of selenium in the feed and in the animal tissues. The aim of the study
was to determine and compare the serum content of selenium in horses in relation to the feeding season. The horses were
used for recreation and sport. Blood was collected from the jugular vein into sterile test tubes without coagulant. In the
mares that did not receive selenium supplements, a very low serum level of selenium was observed. The values were far
below the norms established for horses (100 µg/l -200 µg/l) and ranged from 20 µg/l to 38 µg/l. The level of selenium in
the mares which received pure selenium or selenium in the form of mineral preparations ranged from 56 µg/l to 85 µg/l.
However, this level is still below the reference values. The geldings that received selenium, mineral and vitamin
supplements and special feed had an appropriate level of selenium in the blood. The horses that did not receive selenium
as a supplement had a low level of selenium, well below the norm.
Key words: Disease; Horse; Nourishment; Selenium.
INTRODUCTION
Selenium is an essential microelement for the
proper growth and development of the body. It is present
in the body mainly in compound form, as selenocysteine.
It plays a key enzymatic and structural role in the cell. It
stimulates the immune system to produce antibodies, thus
increasing immune cell activity. Selenium in the cell
functions as an antioxidant, protecting the organism
against the harmful effects of free radicals. By increasing
immune cell activity and inhibiting the development of
tumour blood vessels, selenium acts as a tumour
inhibitor. The protective role of this element against pro-
oxidants is mainly due to its presence in the active centre
of antioxidant enzymes (Combs et al., 1998, 2001).
A factor significantly influencing the amount of
selenium in the body is its content in animal feed. Feeds
of animal origin contain more selenium than plant-based
feeds. The selenium concentration in the blood is higher
in carnivorous or omnivorous animals than in herbivores.
Due to the specific character of their digestive system, the
lowest concentration of this element is noted in ruminants
(Härtlová et al., 2008).
Horses frequently suffer from selenium
deficiency. Given the role the element plays in the body,
horse diets must be supplemented with selenium. The
simplest means is injection or the use of appropriate feed
additives (Muirhead et al., 2010). Selenium
supplementation is required in areas with low soil content
of selenium, particularly if the horses are fed in a pasture
system or if their feed is obtained from such areas. The
risk of selenium deficiency is lower for horses fed on
industrial feeds, as these are supplemented with mineral
additives. When horses are pastured, however, the feed
ration must be supplemented with selenium (Karren et
al., 2010; Brummer et al., 2013a,b).
Selenium deficiencies in horses are determined
geographically and depend on the chemical composition
of the soil in areas used for pasture. The lowest plasma
selenium concentration is found in Australian horses and
in horses from Luxembourg. The highest level of this
element is found in Dutch and Danish horses. Selenium
deficiency in horses is defined as a level below 55–75
μg/l in whole blood (Figueira, 2009). A deficiency of this
element is noted in horses that graze on pastures with
selenium-poor soil or whose diet is based on feed from
such areas which is not supplemented with organic or
inorganic selenium (Janicki et al., 2001; Kienzle et al.,
2006; Brummer et al., 2013a,b). In Poland the selenium
level in horse blood is below the norm in practically the
entire country (Monkiewicz et al., 2013). A similar
problem exists in the Czech Republic, where selenium
deficiency was diagnosed in half the population of
domestic horses (Figueira, 2009). Among German horses
from Bavaria, despite selenium deficiency only 50% of
the population receives feed supplemented with selenium
(Avellini et al., 1999).
The aim of the study was to determine and
compare the serum content of selenium in horses in
relation to the feeding season.
The Journal of Animal & Plant Sciences, 27(5): 2017, Page: 1448-1453
ISSN: 1018-7081
Wyganowska et al., The J. Anim. Plant Sci. 27(5):2017
1449
MATERIALS AND METHODS
The study was carried out according to the
guidelines of the III Ethical Committee in Warszawa (No
37/2011).
Ten horses (5 mares and 5 geldings), kept in
similar conditions, were selected for the study. The
horses were used for recreation and sport. All of the
horses received three meals a day. The meals consisted of
barley and oats and always hay (twice a day in the
pasture season and three times a day in the winter
season). The horses were let out to paddocks every day.
Twice a week during the winter season the animals
received mash and had permanent access to water. The
study was conducted in two periods: after the pasture
season (end of November 2015) and at the beginning of
the pasture season (end of May 2016). Blood was
collected from the jugular vein into sterile test tubes with
no coagulant. The animals were in good health at the time
of blood collection. Selenium in the serum was
determined by ICP-MP. Table 1 presents the horses’ diet
in detail.
RESULTS
In accordance with the planned timetable,
analyses of selenium content in the blood of the ten
horses were performed after the end of the pasture season
(in November) and before the start of the pasture season
(end of May).
Marked selenium deficiencies were observed in
most of the horses. After the pasture season eight of the
ten horses had a selenium level below the reference
value. These included all of the mares tested and three of
the five geldings. After the autumn-winter season, before
the start of the pasture season, selenium deficiency was
noted in all of the mares and in one of the geldings. The
mares that did not receive selenium supplements had a
very low level of selenium in the blood. The values were
below the norms established for horses (100 µg/l -200
µg/l) and ranged from 20 µg/l to 38 µg/l. The level of
selenium in the mares which received pure selenium or
selenium in the form of mineral preparations was nearly
twice as high, ranging from 56 µg/l to 85 µg/l. However,
this level is still below the reference values. The geldings
that received selenium, mineral and vitamin supplements,
and special feed had an appropriate level of selenium in
the blood. The horses that did not receive selenium as a
supplement had a low level of selenium which was well
below the norm. Table 2 presents the results of the
analyses of selenium content in relation to the feeding
season.
Table 1. Description of the horses’ diet.
Individual/Bree
d/Age
Pasture season
Non-pasture season
Mare 1
Trakehner
9 years
receives electrolytes
diet: 1 kg oats and 1 kg barley
used for sport (riding 5 times a week)
receives electrolytes
diet: 1 kg oats and 1 kg barley
used for sport (riding 5 times a week)
Mare 2
Wielkopolski
12 years
diet: 3 kg oats
use for recreation (riding 3 times a
week)
diet: 3 kg oats
used for recreation (riding 3 times a
week)
Mare 3
Polish Half Bred
14 years
diet: 1.5 kg oats, herbs (Boswellia), oils,
muesli, vitamins with selenium and zinc
selenium in injections 10 ml
yeast (Yarrowia Equinox)
used for recreation (riding 3 times a
week)
diet: 1.5 kg oats, herbs (Boswellia), oils,
muesli, vitamins with selenium and zinc
selenium 20mg/kg
used for recreation (riding 3 times a
week)
Mare 4
Wielkopolski
14 years
receives electrolytes
diet: 2 kg oats, yeast (Yarrowia
Equinox), pure selenium, Hesta Plus
Selen selenium preparation
used for sport (riding 5 times a week)
diet: 2 kg oats, yeast (Yarrowia
Equinox), pure selenium, muesli, Hesta
Plus Selen selenium preparation
used for sport (riding 5 times a week)
Mare 5
Polish Half Bred
12 years
receives electrolytes
diet: 0.5 kg oats, 1.5 kg barley,
vitamins, mash, linseed, bran
used for sport (riding 5 times a week)
0.5 kg oats and 1.5 kg barley, vitamins,
mash, linseed, bran
used for sport (riding 5 times a week)
Gelding 1
Trakehner
receives electrolytes
diet: 1.5 kg oats, 0.5 kg barley,
diet: 1.5 kg oats, 0.5 kg barley,
electrolytes, vitamins (Marstall)
Wyganowska et al., The J. Anim. Plant Sci. 27(5):2017
1450
11 years
electrolytes, vitamins (Marstall)
used for sport (riding 5 times a week)
used for sport (riding 5 times a week);
electrolytes
Gelding 2
Polish Half Bred
8 years
diet: 2.5 kg oats, no supplements;
used for recreation (riding 3 times a
week)
diet: 2.5 kg oats, no supplements;
used for recreation (riding 3 times a
week)
Gelding 3
Polish Half Bred
12 years
diet: 3 kg oats, 2 kg barley, vitamins
(Marstall), Hesta Plus Selen selenium
preparation, selenium, receives
balanced rations of feed for sport horses
used for sport (riding 5 times a week)
diet: 3 kg oats, 2 kg barley, vitamins
(Marstall), Hesta Plus Selen selenium
preparation, selenium, balanced rations
of feed for sport horses
used for sport (riding 5 times a week)
Gelding 4
Trakehner
8 years
diet: 1.5 kg barley, Nelson protein
supplement, Pavo feed, Cortaflex
supplement
used for sport (riding 5 times a week)
diet: 1.5 kg barley, Nelson protein
supplement, Pavo feed, Cortaflex
supplement
used for sport (riding 5 times a week)
Gelding 5
Trakehner
12 years
diet: 1.5 kg barley, Nelson protein
supplement, Pavo feed, Cortaflex
supplement
used for sport (riding 5 times a week)
diet: 1.5 kg barley, Nelson protein
supplement, Pavo feed, Cortaflex
supplement;
used for sport (riding 5 times a week)
Table 2. Selenium content in the blood of the horses depending on the feeding season.
Selenium level (µg/l)
Reference value
(µg/l)
End of November
(after pasture season)
End of May
(before pasture season)
100-200
26
20
100-200
61
36
100-200
60
64
100-200
56
85
100-200
35
38
100-200
57
105
100-200
82
36
100-200
74
144
100-200
141
101
100-200
162
140
DISCUSSION
Information on the role of selenium in the diet of
horses, as a species and in relation to sex, age and type of
use, can be found in the Polish and world literature.
Nevertheless, it remains a timely topic and has not been
fully described to the satisfaction of horse breeders. All
authors observe selenium deficiency in horses. This
deficiency is the cause of numerous diseases and
dysfunctions and is regarded as a problem in raising these
animals. Our study is the first to draw attention to the
selenium level in the blood of horses in relation to the
feeding season.
The study found a selenium deficiency in most
of the horses tested. Selenium content in the blood of the
animals was well below reference values for the species.
The horses that received selenium supplements had a
higher level of selenium in the blood. The
supplementation was insufficient in the mares, as despite
the addition of selenium to their feed its level in the blood
was still below the norm. Geldings whose feed was
supplemented with selenium preparations had an
appropriate level of selenium. In both males and females
the level of selenium varied depending on the feeding
season.
Pregnant mares in particular should have the
selenium level monitored in their feed and blood (Ishii et
al., 2002; Katz et al., 2009). Adding selenium to the feed
of pregnant mares is recommended, as it substantially
raises the level of selenium in the foetus (Janicki et al.,
2001; Figueira,2009; Karren et al., 2010). Selenium
deficiencies in the diet of mares can result in nutritional
muscular dystrophy in foals. The amount of selenium in
feed for mares should be adjusted for the period of
pregnancy and especially optimized in the final trimester.
The level of selenium supplementation depends on the
selenium content in the feed, and according to various
authors should range from 0.6 mg a week to 1 mg per day
(Katz et al., 2009; Karren et al., 2010) or even up to 3
Wyganowska et al., The J. Anim. Plant Sci. 27(5):2017
1451
mg per day (Janicki et al., 2001; Figueira, 2009). In
extreme cases, when the land is particularly poor in
selenium and yet the mare does not receive mineral
supplements with higher selenium content during
pregnancy, a selenium preparation must be given to the
foal. This is usually an intramuscular injection of 2.5 mg
per 45 kg body weight. The procedure should be repeated
after two and six weeks (Katz et al., 2009).
Selenium deficiencies are dangerous in sport
horses, particularly those undergoing intensive training.
Physical exertion increases the level of reactive oxygen
species in the blood. Selenium reduces the level of
oxidative stress and counteracts negative changes in the
skeletal muscles (Avellini et al., 1999; Deaton et al.,
2002; Härtlová et al., 2008; Dias, 2009). Although sport
horses are fed according to rigorous requirements and
receive selenium supplements, they too may suffer from
muscular system dysfunction (Kienzle et al., 2006). A
reduced serum level of selenium is correlated with
inferior performance in sport horses, particularly in speed
disciplines (Haggett et al., 2010).
Physical exertion increases production of
reactive oxygen species, which can result in redox
imbalance. A deficiency of antioxidants may lead to
oxidative stress. Selenium is one of many catalysts of
antioxidants and is a component of glutathione
peroxidase. Animal feeds differ considerably in selenium
content, and a poor diet can lead to clinical deficiencies
in horses. Racehorses are at risk of oxidative stress due to
long periods of aerobic exercise, and their performance
may depend on selenium levels (Haggett et al., 2010).
Selenium is a very important element in the diet
of animals used as breeders. It affects semen quality and
fertility parameters. Stallions receiving additional
selenium in their feed ration have shown better semen
parameters and higher fertility in comparison with
controls (Bertelsmann et al., 2010; Contri et al., 2011).
The perinatal period is associated with an
increased risk of selenium deficiency, as the
concentration of this element drops during pregnancy
(Dias, 2009; Contri et al., 2011). Selenium deficiency
may have a negative effect on reproduction and on
immune function. It can also cause a reduction in weight
gain (Kirschvink et al., 2002; Bertelsmann et al., 2010;
Contri et al., 2011; Rad et al., 2013). However, it is
primarily the cause of nutritional muscular dystrophy,
also known as white muscle disease. This is a disease in
which the skeletal and heart muscles undergo
degeneration. It occurs mainly in young foals (Youssef et
al., 2013). An inadequate level of selenium in the diet of
mares increases the risk of the disease in foals. Clinical
symptoms of the disease include weakness, muscle
stiffness and fasciculations. Young horses have difficulty
moving and are unable to stand up unassisted. Their
sucking reflex is impaired and they suffer from dyspnoea.
The acute form of the disease is fatal (Karren et al., 2010;
Youssef et al., 2013).
Myopathy caused by a low selenium level also
occurs in adult horses. Its first symptom is problems with
food intake, due to degenerative changes in the
mandibular muscles. Most cases of myopathy described
in the literature have been fatal (Pagan et al., 1999;
Calamari et al., 2009, 2010; Montgomery et al., 2012a,b;
Streeter et al., 2012; Gordon et al., 2013).
A decrease in the selenium concentration in the
blood is also observed in horses used intensively for
recreation. During the summer holiday season, the
selenium level in the blood of horses working about 6
hours a day decreases by about 30%. Such changes have
not been noted in horses that had lighter work or worked
fewer hours. The problem of decreased selenium levels in
recreational horses is also observed in Canada and the
Czech Republic. In horses training intensively problems
with selenium deficiency are less severe. This is probably
due to appropriate supplementation in the case of these
horses and negligence in the case of recreational horses
(Hoff et al., 1998; Figueira, 2009).
Selenium, while essential for life, in excessive
amounts can be highly toxic. The most common diseases
and degenerative disorders caused by selenium deficiency
include muscle degeneration, diarrhoea, and problems
with fertility. Selenium also takes part in detoxification of
the body, and its antioxidant activity has an antitumour
effect. Selenium deficiency is linked to cataracts,
ischaemic heart disease, asthma and cancer. Essential
elements should be supplied in appropriate proportions
and in an easily assimilated form. Selenium is a
submicroelement, which means its level in the body must
be strictly limited and an excessive amount is highly
toxic. It is best assimilated in the form of
selenomethionine and selenocysteine, which are involved
in numerous transformations in the body of animals and
humans.
Conflict of interest statement: None of the authors has
any financial or personal relationships that could
inappropriately influence or bias the content of the paper.
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... Mineral imbalances play a significant role in health problems in horses (Yashiki et al. 1995;Stanek et al. 2016). Mineral nutrients in feed rations for horses are derived from bulky feed, concentrate feed, and mineral supplements (Wagner et al. 2011;Dominguez-Vara et al. 2017;Wyganowska et al. 2017). Feeds used in horse diets are usually locally produced. ...
... Micronutrients, such as copper, zinc and selenium, perform equally important functions (Korpal et al. 2016;Stanek et al. 2016). East-central Poland has good geographical conditions for raising livestock, but deficiencies in the supply of minerals to horses are observed in this region (Wyganowska et al. 2017). The aim of the study was to determine characteristics of the mineral metabolism of horses raised in a region characterized by mineral deficiencies as a basis for evaluating their diet. ...
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This study investigated the effects of administering vitamin E and selenium to pregnant heavy draft horsemares on the incidence of retained placenta and postpartum reproductive performance and on the prevention of the white muscle disease in their foals. In study A, 1,000 mg of vitamin E and 50 mg of selenium (E-SE 20 mL) were given to 22 mares 3 weeks before expected parturition (335 days counted from last mating), whereas 28 mares were used as controls. In study B, E-SE were administered 2 weeks before expected parturition at 2 dose levels, with 25 mares receiving 20 mL E-SE, 19 mares receiving 10 mL, and 29 mares kept as controls. Vitamin E and selenium were assayed in serum collected from some of the mares before administration of E-SE and again postpartum and from the foals immediately after birth. Serum selenium concentrations before E-SE administration were deficient (<65 ng/mL) in all mares (n = 48) but were increased in the postpartum sample from treated mares regardless of the dose or timing of administration (n = 31) (P = .05). Only study B mares were deficient in vitamin E prepartum, and both dose levels of E-SE had corrected this in the postpartum sample (P = .01). All foals were selenium deficient regardless of whether their dams had received E-SE or not, although concentrations were higher in foals from treated study A mares than from controls (P = .05). Mares with the highest selenium concentrations prepartum (40 ng/mL and over) had shorter placental retention times than mares with lower selenium concentrations (P = .05) and did not respond to E-SE with a further reduction in retention time. By contrast, mares with prepartum selenium concentrations between 20 and 40 ng/mL tended to respond to E-SE with a shortened placental retention time (P = .07). E-SE administration reduced the mean number of days from parturition to last mating (nonpregnant term) in study B mares (P = .05) and in mares with adequate prepartum vitamin E concentrations (>300 g/mL, P = .05). We conclude that maintaining high level serum vitamin E and selenium concentrations of prepartum mares is expected to increase fertility of selenium-deficient mares. Therefore, the regimen of vitamin E and selenium administrations to selenium deficient mares should be developed.
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Selenium status has been reported to affect immune function across many different species. Yet few studies have focused on the effect of Se status on the equine immune system. This study examined the effect of Se supplementation on vaccination response and immune function in mature horses. Twenty-eight horses were blocked by age and sex, and randomly allocated to 1 of 4 dietary treatment groups: low Se (LS), adequate Se (AS), Se-yeast (SP) and, sodium selenite (SS). For 35 wk, horses allocated to LS, SP and SS received a low-Se diet (0.06 mg/kg DM) with the intention to lower Se stores, while AS received an adequate Se diet (0.12 mg/kg DM). A 29-wk repletion phase was as follows: LS and AS were kept on the diets fed during the depletion period, while SP and SS received the depletion diet plus their respective Se supplements to achieve a dietary Se concentration of 0.3 mg/kg DM. The Se status of the horses was monitored using whole blood Se and glutathione peroxidase (GSH-Px) activity as indicators. At wk 22 and 25 of the repletion phase, horses were vaccinated intramuscularly with 10 mg ovalbumin (OVA). Horses were also vaccinated against equine influenza at wk 25. Blood samples were collected for 7 wk following initial vaccination for serum separation, and at 0, 3 and 5 wk post vaccination for peripheral blood mononuclear cell (PBMC) isolation and whole blood cytokine mRNA evaluation. At wk 22 of the repletion phase, both Se and GSH-Px were greater for SP and SS compared to AS and LS (P < 0.001). Serum vitamin E was similar between treatments. Response to OVA vaccination, evaluated as OVA specific IgG production, cytokine mRNA expression of PBMC stimulated with OVA in vitro, and lymphocyte proliferation, was unaffected by Se status. Similarly, memory response to the influenza vaccine was not affected by Se status. However, lower mRNA expression of selected cytokines was observed in PBMC stimulated with phorbol 12-myristate 13-acetate for LS as compared to AS, SP, and SS (P < 0.05). Whole blood mRNA expression of IL-10 was greater for SS compared to LS, AS, and SP (P = 0.043). Although the OVA and influenza vaccination responses were unaffected by Se status, other measures of immune function did indicate that low Se status could adversely affect cell-mediated immunity.
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Selenium plays a role in the antioxidant mechanism via the selenoenzyme glutathione peroxidase (GSH-Px). Change in Se status because of Se depletion or supplementation is associated with a change in GSH-Px activity and could potentially affect antioxidant status. This study evaluated the impact of change in Se status on measures of antioxidant status and oxidative stress in adult horses. Twenty-eight horses were blocked by age and gender, and randomly allocated to 1 of 4 dietary treatment groups: low Se (LS), adequate Se (AS), high organic Se (SP), and high inorganic Se (SS). For 196 d, LS, SP, and SS received a low-Se diet (0.06 mg Se/kg DM) to allow for depletion of Se stores, while AS received an adequate Se diet (0.12 mg Se/kg DM). Then, for the next 189 d, LS and AS were maintained on the same diets, while SP was supplemented with Se-yeast and SS with sodium selenite to allow for a total dietary Se intake of 0.3 mg Se/kg DM. Blood samples were collected throughout the study. Variables of interest included whole blood Se and GSH-Px activity, serum vitamin E concentration, total antioxidant capacity (TAC), serum malondialdehyde (MDA), and triiodothyronine and thyroxine levels. Data were analyzed using ANOVA with repeated measures. Whole blood Se and GSH-Px activity decreased in LS, SP, and SS during depletion phase and increased in SP and SS with supplementation (treatment x time, P < 0.001). At the conclusion of the supplementation period, GSH-Px activity was greater in SP and SS compared to AS and LS (P < 0.05). Vitamin E status remained adequate throughout the study and no differences existed between treatments. Serum TAC did not change in response to Se depletion or repletion. Serum MDA was greater for AS than LS during depletion (P < 0.05) but similar across treatments after supplementation. Overall, change in Se status did not have a large impact on TAC or MDA, possibly because the horses maintained an adequate vitamin E status. However, Se supplementation at 0.3 mg/kg DM increased GSH-Px activity above that of the horses fed an adequate diet based on the 2007 NRC, indicating a potential benefit to feeding higher Se diets to horses kept in low-Se areas.