Feed International - August 2017 - 17
FeedInternational ❙ 17
reduced back to Vitamin E. As well
as an antioxidant, Vitamin E also
has specific effects on macrophages.
Vitamin E requirements are related
to the complex inter-relationship
between Vitamin E, Se deficiency
and quantities of UFA in the diet.
Indeed, many of the studies showing
supplementation of Vitamin E reduces the incidence of mastitis were
carried out in Se-deficient herds.
Optimizing is essential
Se-containing enzymes also
scavenge ROS and have a vitamin
E-sparing effect. Levels of selenoenzymes are known to decrease during
the periparturient period but rapidly
increase again in early lactation.
This decrease may partly contribute
to the immunosuppression seen in
periparturient cows. Glutathione
peroxidase is a selenium-containing
enzyme that oxidizes glutathione
in the presence of peroxides where
GSH = reduced glutathione and
GSSG = oxidized glutathione:
2GSH + H2O2 → GSSG + 2H2O
Selenium inadequacy is also
linked with adverse immune function effects, such as impaired
antibody production and reduced
phagocytotic capacity. Adequate selenium status has a positive effect on
the animal's ability to resist infection, as well as fertility parameters.
One of the ways selenium exerts
its effects on the immune system
IMMUNE FUNCTION IS CRITICAL
to dairy cow performance.
is via Interleukin 2 (IL-2), which
is involved in T cell proliferation
and differentiation. Interleukin 2
(IL-2) is directly related to selenium
levels, hence, poor selenium status
is reflected in an inability to mount
a good T-cell response whether to a
pathogen itself or to a vaccine.
Optimizing Se status in cows
is essential for supporting immune
function, and not only the amount but
the form of Se supplied is important.
It is well established that organic
forms of minerals generally have
higher bioavailability and retention
in the body compared with their inorganic counterparts. This retention
in body tissues allows the animal to
build a reserve of the mineral to use
in times of increased physiological
stress, e.g. transition. As Se cannot
be chelated, selenium-enriched yeast
(Se-yeast) is often used to deliver Se
in an organic form.
Minerals and immunity
Positive effects have been noted
with feeding an organic form of other minerals, such as zinc and copper.
Zinc deficiency can result in immune abnormalities and subsequent
greater vulnerability to infections.
A decrease in lymphocyte proliferation, as well as reduced phagocytotic
activity, has been demonstrated following zinc deficiency. Interestingly,
disruption of immune function has
also been noted following an excess
of zinc, which highlights the possible role of zinc in immune regulation. Zinc is also crucial for maintaining the integrity of the primary
barrier, the skin. Cells involved in
the innate response require zinc for
normal function and development.
Copper is also crucial for immune function. It affects the interleukin responsible for T cell proliferation in the adaptive response.
Neutrophil proliferation is also affected by copper deficiency. Hence,
copper-deficient animals often show
Essentially, immune function is
critical to dairy cow performance,
and attention should be paid to promoting it throughout the dry and
transition period. Nutrition plays a
crucial role in dairy cow health, not
least through direct effects on the
immune system. Feeding to enhance
immunity is vital and should focus
on maintaining rumen function, as
well as providing optimal mineral
nutrition. There are also feed ingredients and additives that can be utilized to support immune function. ■
References available upon request.
Dr. Helen Warren is the owner of HW Consulting. She is a registered animal scientist and certified Cow Signals trainer.
August/September 2017 ❙ www.WATTAgNet.com