Biomedical Engineering Reference
In-Depth Information
is involved in detoxifying superoxide radicals
(free oxygen radicals) produced by immune cells
in response to kill bacteria. Superoxide radicals
disrupt cellular membranes and cause cellular
damage leaving the mammary gland more sus-
ceptible to infection, scarring and loss in milk
production. Manganese also enhances macro-
phage (white blood cell) killing ability. Increasing
copper and manganese status of the lactating cow
can help reduce SCC as copper and manganese
play roles in immune response.
under metabolic and physiological stress during
early lactation. State of negative energy balance
may increase concentration of nonesterified fatty
acids (NEFA) and b-hydroxyl butyric acid
(BHBA) in blood which result in ketosis and
other metabolic disorders. The supplementation
of Cr is beneficial during the early lactation and
immediately after parturition in cows. During the
periparturient period, insulin resistance may be
an important factor in the initiation of catabolic
activities (Holstenius
1993
) . Improved glucose
tolerance and milk yield and decreased blood
cortisol, NEFA and BHBA were observed in
primiparous cows supplemented with 0.5 ppm
of organic chromium (Subiyatno et al.
1996
) .
Supplementation of chromium has been obser-
ved to reduce blood cortisol concentrations and
increase measures of immunological activity in
transition dairy cows (Burton et al.
1993
; Chang
et al.
1996
) .
7.2.6 Chromium
Chromium has both humoral and cellular immu-
nomodulatory effects, but the fundamental mecha-
nism of intercellular and intracellular action are
still to be fully elucidated. Cr requirements in
human and farm animals increase during stress,
the heat stress and early lactation could excrete
Cr irreversibly through urine (Borel et al.
1984
) .
Heat stress decreases feed intake and adding Cr
to the diet help relieve this effect (AL-Saiady
et al.
2004
; Hayirli et al.
2001
). Cows fed the diet
with Cr had the highest peak milk production
over the control. The increased milk yield could
also occur due to higher dry matter intake and
reduced rate of mobilisation of fatty acids from
adipose tissue (McNamara and Valdez
2005
) . Cr
deficiency can cause insulin resistance, and the
ratio of glucose to insulin can act as a crude index
of tissue sensitivity to insulin (Evock-Clover
et al.
1993
). Cows receiving Cr had higher molar
ratio of glucose to insulin and lower insulin than
cows receiving no Cr indicative of increased
insulin sensitivity due to Cr supplementation.
Increased insulin sensitivity is likely to stimu-
late lipogenesis and inhibit lipolysis. A reduced
mobilisation of fatty acids from adipose tissue
may allow a greater increase in feed intake, stabi-
lise hepatic fat metabolism and reduce hepatic
ketogenesis, to increase milk production in cows
(Kronfeld
1976
) .
The immune function may be affected by low
Cr levels in association with insulin and/or cor-
tisol activity as corticosteroids suppress immune
system. The chromium also mediates production
and regulation of certain cytokines (Borgs and
Mallard
1998
) . High-producing dairy cows are
8
Effect of Free Radical
Production on Immunity
and Role of Antioxidants
An increase in oxidative reactions within the cell,
or at the cell membrane, produces free radicals or
activated molecules with the potential to inhibit
cellular functions, damage membranes and even
to result in the destruction of the cell. Oxidation-
reduction reactions do normally occur in the body,
but when the reactions become uncontrolled, the
end products of oxidation (i.e. free radicals) accu-
mulate, and tissue damage occurs. In an effort to
protect itself, the cell prevents the accumulation
of free radicals by the action of several antioxi-
dants present in the body (Table
3
).
Various factors facilitate the accumulation of
free radicals, but heat stress increases both the
metabolic rate of cells and free radicals accumu-
lation (Bernabucci et al.
2002
; Lohrke et al.
2005
;
Chandra
2009
). If the levels of antioxidants pres-
ent are low/suboptimal within the cell, the dam-
age due to accumulation of free radicals is likely
to occur. Cows that are under stress of calving,
challenged by a high load or experiencing the
peak demands of lactation, have a higher level of
