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Copper
Toxicity in Sheep
(also relevant to goat and llama feeds) |
It is well known that sheep are extremely sensitive to copper.
They will suffer from hypocuposis (copper deficiency disease)
if not receiving adequate amounts in the diet or if antagonists
interfere with copper metabolism even when nominally appropriate
dietary levels are present. Excess levels of zinc, iron, sulfur
and molybdenum can each interfere and cause deficiencies1.
On the other hand, sheep are also unusually intolerant of
higher levels of copper and can be killed by levels routinely
added as beneficial to the diets of swine and poultry. Nutritionists
must strike a difficult balance because many feedstuffs contain
enough sulfur and molybdenum to antagonize copper metabolism.
In such cases, it may be necessary to provide copper as much
as several fold higher than the nominal nutritional level
to avoid deficiency disease2. The difficulty occurs
because such copper levels can be dangerously high if the
level of antagonists is misjudged or changes over time.
TBCC in Sheep Feed
Micronutrients TBCC®
(TBCC) offers an advantage in ruminants because it is less
reactive with sulfur and molybdenum in the rumen3
and therefore provides a more stable, predictable level to
the animal as these antagonists vary in the diet. This is
particularly important when the animals are grazing since
the dose levels of the antagonists are more variable. Thus,
TBCC helps avoid the dual problems of copper toxicity and
deficiency.
Issues
in Manufacturing Sheep Feed
- Batch Sequencing
- To the extent possible, a batch of sheep feed should
never be made following a concentrated feed mix. If
such sequence is unavoidable, the copper salt should
not be the last ingredient added to the concentrated
feed and all equipment should be thoroughly "flushed"
with an inert ingredient prior to starting the sheep
feed. These same precautions should actually be used
when making a complete feed for any species.
- Copper Assay of TBCC
- TBCC has a copper concentration 2.3 times higher
than copper sulfate (58% vs. 25%). This is an important
advantage since it reduces freight and labor costs
to handle the product and it provides more "space"
in a mix for other ingredients. Any inadvertent carryover
in feed manufacturing could have a correspondingly
higher impact, just as it would with copper oxide.
Thus, good mill practice is particularly important.
- Particle Size
- The particle size of an ingredient can impact carryover
in feed mill equipment. This effect is only significant
for particles smaller than 20 micron. Below this size,
many materials behave as dusty powders and can carry
an electrostatic charge which causes them to cling
to equipment surfaces. TBCC is a fine grained material
which is advantageous for blending and handling, but
virtually none of the mass of the material is below
the 20 micron threshold. Conversely, many other feed
grade sources of copper contain an appreciable amount
of fines or dust below this size which can be electrostatically
charged. In fact, users of TBCC report that avoidance
of copper sulfate dust is one of the benefits of using
the product. Therefore, caution and good mill practice
are essential with all sources of copper.
Summary
TBCC is a preferred source of copper for sheep since it helps
with the nutritional challenge of staying in the target window
between copper deficiency and toxicity.
Multi-purpose mills should take great care to avoid carryover
of copper (and other minerals) when making sheep feed - regardless
of the copper source being used. Four suggestions are:
- Flush or clean all equipment thoroughly before making
a batch of sheep feed.
- Adjust batch sequences to avoid making sheep feed immediately
after a high-copper feed.
- Avoid running copper or a mineral premix through conveying
equipment as the last ingredient in a batch, especially
when the next batch will be sheep feed.
- Because of the criticality of copper in sheep, each
batch of sheep feed should
be assayed before release.
References
- Clarence B. Ammerman and Pamela R. Henry, presented
at the Copper and Health in Ruminants Symposium organized
by the Pacific Northwest Chapter of the American Registry
of Professional Animal Scientists, and held in Seattle,
WA on May 25,1996.
- "Copper Deficiency Overview with Particular Reference
to Copper-Molybdenum-Sulfur (Cu x Mo x S) Interaction
in Ruminants", N. F. Suttle, presented at the Copper and
Health in Ruminants Symposium organized by the Pacific
Northwest Chapter of the American Registry of Professional
Animal Scientists, and held in Seattle, WA on May 25,1996.
- "Bioavailability of Copper from Copper Chloride in Cattle",
an unpublished report on a cattle feeding study done by
Jerry W. Spears at North Carolina State University. Copies
available from Micronutrients
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