Biomedical Engineering Reference
In-Depth Information
trace elements involved in animal feed are Zn,
Cu, selenium (Se), iron (Fe) and manganese (Mn)
(Surai et al.
2003
; Surai and Dvorska
2002
) .
The mineral-dependent antioxidant enzymes
that can be synthesised in the body are able to
deal effectively with free radicals but require a
continuous supply of feed-derived mineral cofac-
tors. Selenium (Se) is an essential part of a
family of enzymes called glutathione peroxi-
dases (GSH-Px) and thioredoxin reductases
(Berry et al.
1991
). However, Zn, Cu and Mn are
integral parts of superoxide dismutase (SOD),
and Fe is an essential part of catalase. When
these metals are supplied through feed in sufficient
quantities, adequate antioxidant enzymes are
synthesised in the body. However, deficiency of
these elements results in oxidative stress, leading
to potential damage of tissues, biological mole-
cules and membranes.
(Chawla and Kaur
2005
; Chandra and Aggarwal
2009
). The vitamin E content of basal diet is
highly variable; therefore, NRC (
2001
) has rec-
ommended supplemental vitamin E regardless of
the dietary vitamin E content. The requirements
that are based on measures of immune function
are usually higher than those based on production
or reproduction. NRC (
2001
) has suggested the
requirement of vitamin E during last 60 days of
gestation: 80 IU/kg DMI for dry cows and 20 IU/
kg DMI for lactating cows. Selenium should be
provided only if the soil is deficient in selenium
in that particular area.
Although Se and vitamin E functions indepen-
dently, studies have shown that administration of
both Se and vitamin E may result synergistically
to enhance immune response (Spears
2000
).
Vitamin E supplementation of lactating dairy
cows (Hogan et al.
1990
) and young calves fed
on a milk substitute (Eicher et al.
1994
) also
increased blood neutrophil bactericidal activity.
Compared with non-vitamin E-supplemented
cows, supplementing dairy cows with 3,000 mg
vitamin E per day for 4 weeks prepartum and
8 weeks postpartum prevented a decline after
parturition in neutrophil superoxide anion pro-
duction and IL-1 production and major histocom-
patibility class II antigen expression by blood
monocytes (Politis et al.
1995
) .
Se plays an important role in removing hydro-
gen peroxide and organic hydroperoxides
through its effects as a component of the antioxi-
dant enzyme glutathione peroxidase, and a
deficiency in Se can induce a state of oxidative
stress in the host (Chaudiere and Tappel
1984
) .
Se deficiencies have been reported to associate
with lower resistance to infections, possibly due
to decreased antibody production and an impaired
lymphocyte proliferative response (Chandra and
Chandra
1986
; Reffett et al.
1988
) . However,
other studies have identified additional mecha-
nisms by which Se supplementation enhances
immune function, including neutrophil killing
activity (Hogan et al.
1990
) and neutrophil adher-
ence (Maddox et al.
1999
) . The altered neutro-
phil adherence could also affect the ability of
neutrophils to attack and sequester pathogens
(Spears
2000
) .
7.2.1 Selenium (Se)
Selenium is an essential component of a range of
selenoproteins, including glutathione peroxidase,
thioredoxin reductase and iodothyronine deiodi-
nase. Selenium is found in raw feed materials
used for animals in varying quantities, and some
of them are deficient or may have higher toxic
levels. There are two major sources of Se for ani-
mals: (1) Se from feed materials, in the form of
selenoamino acids, including selenomethionine
and selenocysteine; (2) inorganic Se in the form
of selenate or selenite. The physiological require-
ment for Se is low in animals, but if this is not
met, the antioxidant system is likely to be com-
promised and may affect animal health (Spears
2000
). Excessive levels of Se (in plants and soils)
are associated with toxicity; therefore, adequate
measures need to be adopted for preventing
toxicity of selenium.
Selenium content of feeds may vary as per the
soil content. Vitamin E and selenium supplemen-
tation are required or may be necessary to enhance
the body defences from challenge of infectious
agents. Supplementation of 0.3 ppm Se and
500 IU/day vitamin E during lactation and vita-
min E 1,000 IU/day during the dry period has
been shown to reduce prevalence and severity of
mastitis and reduce somatic cell count in milk
