Volume 23 • Issue 01 • 2019
at concentrations less than 100 parts per million
(ppm, also known as mg per kg) of the diet. The
National Research Council (NRC) has identified
10 trace minerals as essential for beef cattle.
However, only about 4 are generally recognized
as the most problematic in grazing beef cattle:
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Copper (Cu)
Zinc (Zn)
Manganese (Mn)
Selenium (Se) - which is a non-metallic
element that exists in several allotropic
forms.
Cattle gain most of their daily trace minerals
from their diets (pastures, water, licks) which is
influenced by various factors such as soil type and
pH, geographical region and rainfall, composition
of diet (stem:leaf ratio, fibre digestibility and
fertilization, sulphur containing amino acids).
Trace mineral nutrition of cattle is further
complicated by antagonistic reactions of
which Calcium (Ca), Iron (Fe), Molybdenum
(Mo) and Sulphur (S) are the main antagonists
in grazed forage and water sources. These
antagonistic reactions mainly take place in the
rumen and negatively affect the absorption and
bioavailability of trace minerals.
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Dietary Ca concentrations have been
demonstrated to differentially affect Zn and
Mn bioavailability. (Green line)
Iron is the second most common trace metal
on earth and is found in nearly all sources
of feed, including water. A considerable
amount of Fe may also be ingested through
the intake of soil during grazing as well as
soil contamination of harvested forage. In
most soils iron is extremely high but with
low solubility. Research indicated that acid
conditions, like fermentation of silage, greatly
increases the bioavailability of iron from soil
contamination. Iron is a potent copper, zinc
and manganese antagonist. (Red line)
Sulphur (S) is found naturally in nearly all
feedstuffs and decrease Cu and Se availability.
(Yellow line)
Molybdenum (Mo) is an essential trace
element required by all animals and
deficiencies are readily recorded. High levels
of molybdenum can impact Cu nutrition in
ruminants by two means: (Yellow line)
º º Irreversibly bind Cu in the gut and
prevent absorption.
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Post-absorption systemic depletion of
Cu from tissue sites.
To minimize the effect of antagonism with oral
supplementation of trace minerals the minerals
can be chelated when fed to the animals.
Research shows that fresh semen sperm motility
was increased from 55.2% to 69.1% in bulls fed
chelated trace mineral supplements.
Oxidative stress.
Bulls, as are all animals, are subjected to various
forms of stress. Such as:
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Nutritional stress
Environmental stress (heat stress, cold,
transportation)
Social stress (comingling and dominance
determination)
Breeding
Diseases and parasite infestation
All of these stress factors contribute to another
type of metabolic stress, called oxidative stress,
which is characterised by an increase in the
amount of free oxygen radicals, and that can
lead to point mutation, a catastrophic snow-ball
reaction of cell dysfunction.
The study of oxidative stress is a relatively
young field of research in ruminant medicine.
Oxidative stress results from increased exposure
or production of oxidants, (which can be seen
as a by-product of most metabolic processes
in the body) or from decreased dietary intake
or increased turnover of antioxidants. Thus,
oxidative stress is a condition that results from
an imbalance between oxidants and antioxidants
in the body.
A limited number of conditions have been
investigated with regard to the effect of oxidative
stress in ruminants. Studies in cattle have
been sporadic and mainly focused on mastitis,
pneumonia, retained placenta, metabolic diseases
and more recently bull fertility.
Essential trace minerals such as zinc (Zn),
selenium (Se), manganese (Mn) and copper (Cu)
not only act as antioxidants but also play vital
roles in multiple metabolic processes.
Oxidative stress (OS) results when the production
of reactive oxygen species (ROS) exceeds the
antioxidant defence mechanisms present in
the body and can lead to DNA damage which is
the root of physiologic and pathologic diseases.
At high concentrations ROS produce adverse
modifications to all cellular components, altering
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