Biomedical Engineering Reference
In-Depth Information
Many of the beneficial health effects of Se are
mediated by antioxidant selenoenzymes, with
selenocysteine at the active sites. Cytosolic gluta-
thione peroxidase (GPX1) is the selenoenzyme
most often associated with antioxidant func-
tions. Determination of cellular or plasma GPX1
activity is a diagnostic tool for assessing Se sta-
tus of dairy cows. Many other bovine antioxidant
selenoproteins exist including selenoprotein P,
five different isoforms of GPX and three thiore-
doxin reductase (TrxR) isoenzymes (Grignard
et al.
2005
; Hara
2001
) . Both GPX1 and TrxR1
play a critical role in reducing both H
2
O
2
and
fatty acid hydroperoxides to less reactive water
and alcohols, respectively.
Zn (about 25 ppm supplemental and 25 ppm from
basal diet). Source of Zn had no effect on infec-
tion rate, new infections, clinical mastitis and
SCC. Animal diets should contain about 20 ppm
of copper and 50-60 ppm of Zn.
Zinc also plays a role in maintenance of
epithelial tissue. Since teat skin is the first line of
defence, any deterioration in the health of epithe-
lial tissue will enhance the ability of bacteria to
penetrate and cause infection. Zinc is also
required for keratin production. Keratin is a wax-
like substance secreted into the teat-end opening.
The keratin lining of the teat canal helps in
entrapping bacteria and prevents their upward
movement into the mammary gland through its
bactericidal properties. Approximately 40% of
keratin in the teat canal is regenerated after each
milking; therefore, the ability of the cow's mam-
mary system to efficiently reproduce keratin is
important in the defence against mastitis.
Zn is also involved in facilitating hormonal
secretion and function particularly somatomedin-
c, osteocalcin, testosterone, thyroid hormones,
insulin and growth hormone. In India, commonly
fed feeds (roughages as well as concentrates)
contain Zn content below the critical level of
40 ppm as recommended by NRC (
2001
) for
dairy cattle. Hence, there is a need to supplement
Zn to dairy animals in order to improve their
immune status.
7.2.2 Zinc (Zn)
Zn is the second most abundant trace element in
mammals and birds and forms a structural com-
ponent of over 300 enzymes and plays catalytic
and regulatory element affecting efficiency
complex. An important role played by zinc is in
antioxidant defence system as an integral part
of the essential enzyme superoxide dismutase
(SOD) (Underwood
1999
; National Research
Council
2001
). Zinc has been reported to influence
several components of immunity, including cell-
mediated immune functions, tissue regeneration,
protein synthesis and inflammatory responses
(Erickson et al.
2000
; Kruse-Jarres
1989
) . Zn
supports humoral and cell-mediated immunity by
facilitating proliferative reactions in response to
stimulus by different mitogens by way of its
action on immune cells as a cofactor for essential
enzymes. Zn deficiency has been associated with
decreased T-cell function and antibody responses
(Kruse-Jarres
1989
) .
Tomlinson et al. (
2002
) have summarised
results of 12 experiments and reported an overall
significant reduction (196,000 vs. 294,000) in
SCC when Zn-Met was supplemented (about
200 mg of Zn/d in five experiments and about
380 mg of Zn/d in seven studies). Whitaker et al.
(
1997
) compared the effects of providing supple-
mental Zn from a mixture of Zn proteinate
(250 mg of Zn/day) and inorganic Zn (140 mg/
day) or from all inorganic sources (390 mg of Zn/
day). Diets contained approximately 50 ppm total
7.2.3 Copper (Cu)
Cu is a component of a range of physiologically
important metalloenzymes and takes part in
(1) antioxidant defence as an integral part of
SOD, (2) cellular respiration, (3) cardiac func-
tion, (4) bone formation, (5) carbohydrate and
lipid metabolism, (6) immune function, (7) con-
nective tissue development, (8) tissue keratinisa-
tion and (9) myelination of the spinal cord. The
main Cu-containing enzymes have been enlisted
in Table
2
. Inorganic Cu has a strong pro-oxidant
effect and likely to stimulate lipid peroxidation in
feed or the intestinal tract (Surai et al.
2003
) .
Dietary Cu may also affect cytokine production
in cattle. Mononuclear cells of lactating dairy
cows receiving a marginal level of Cu (6-7 mg/
kg diet) were observed to produce less IFN-g
