Download - Advit: Animal Nutrition

PRODUCTION
Potent
potassium
by Anelle Wabeke
Potassium is the third-most abundant mineral element in the body after
calcium and phosphorus. It is essential for life as it is involved in the osmotic
regulation of tissue fluids and the acid-base balance that exists between
potassium, sodium, calcium and magnesium. The highest potassium
concentration in the body is found within the muscle cells and comprises
about 5% of the total mineral content of the body.
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PRODUCTION
Ruminants need more
Ruminants have a higher requirement for potassium than monogastric animals, as it is essential for rumen microorganisms. The
requirements are estimated to be between 0,5 and 0,8% of the
diet, which increases under stress conditions. The optimal level
of dietary potassium in high-production dairy cows under heat
stress can increase to approximately 1,1%.
Less potassium (0,65%) is recommended for dry cows, heifers and calves. High levels of potassium in the last three to four
weeks before calving should be avoided as this may increase the
probability of milk fever and retained placentas, which could lead
to reduced milk production. The maximum potassium quantity
allowed in a dry cow ration depends on the use of anionic salts.
It is recommended that fertilised pastures should be avoided
during this stage.
The effect of heat stress
of potassium
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aintain water balance
M
Maintain osmotic pressure
Maintain acid-base balance
Activate enzymes
Help metabolise
carbohydrates and proteins
• Regulate neuromuscular
activity (along with calcium)
• Help regulate heartbeat
UPPE A11198/DM
Heat stress leads to reduced feed intake and production, as well
as a loss of sodium and potassium through sweat. This requires
an increased dietary supply of minerals during hot days. Many
responses to heat stress such as increased water intake, respiration and sweating rates are survival strategies to maintain
normal body temperature. This compromises the optimum efficiency and maximum production of lactating cows. Potassium is
the main mineral in sweat and, as the temperature rises, cows
Functions
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lose more potassium through sweating, panting
and urination. In addition to sweat loss, lactating cows also lose additional potassium via milk,
which contains 0,15% potassium. A cow producing
20 kg milk and consuming 20 kg dry matter containing 0,8% potassium will secrete about 19% of
her daily potassium intake in milk. In addition to
potassium loss through sweat and milk, meeting
the animal’s requirement may be complicated
by suppressed dry matter intake, reducing the
total amount of potassium and other nutrients
consumed.
// A cow producing 20 kg milk and consuming 20 kg dry
matter containing 0,8% potassium will secrete about
19% of her daily potassium intake in milk. ”
Deficiency
signs
Potassium deficiency is uncommon in grazing dairy cows, as green
forages are excellent sources of potassium (1 to 4%).
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epressed growth
D
Muscular weakness
Stiffness
Decreased feed intake
Intracellular acidosis
Nervous disorders
Reduced heart rate
Abnormal electrocardiograms
PRODUCTION
Potassium in the ration
Studies have shown that supplementing dietary
potassium during hot summer days to Holstein cows
increased feed intake and milk yield curvilinear to
dietary potassium, although this response is lower for
Jersey cows and animals under shade.
The maximum tolerable concentration according to the National Research Council (NRC) has
been set at 3% for cattle, but cattle grazing lush
spring pastures often consume more than this with
no adverse effects except for reduced absorption
of magnesium causing grass tetany (this can be
countered by giving extra magnesium). Pasture with
an excess of 5% potassium
can increase the occurrence
of bloat and infertility. Excess
potassium can also aggravate
a sodium deficiency, which is
associated with impaired reproduction. Potassium deficiency
is uncommon in grazing dairy
cows, as green forages are
excellent sources of potassium
(1 to 4%), especially lush spring
pastures. But cows on a total
mixed ration (TMR) are often
deficient in potassium, as TMRs
consist mostly of ingredients
low in potassium such as cereals, hay and silage (although
molasses and seed oils are
good sources). Potassium can
be supplemented by potassium
chloride, potassium carbonate
or potassium sulphate if necessary. When potassium chloride
is used, the total chloride levels
should be no more than 0,3 to
0,35% in the total dry ration.
When potassium is increased
in a ration, other minerals should
be kept in mind too, as minerals have a significant number
of interactions. Many of these
interactions are between potassium, sodium, chloride
and magnesium. Additional magnesium is required
when a ration is fed which contains more that
1% potassium. Potassium supplementation may inhibit magnesium uptake from the rumen and could
result in hypomagnesaemic tetany.
Other adjustments nutritionists can make are to
use high-quality forage to reduce heat production
during digestion and adding water to the total mixed
ration if dry matter intake drops significantly. This can
sometimes increase dry matter intake substantially.
Feeding a higher fat ration (up to 5 to 7% of the total
ration) is also an option if a feed intake of 90% of
normal intake can’t be maintained to increase ration
energy without increasing the heat of rumen fermentation. Increasing bypass protein levels to account for
the decline in dry matter intake is another option.
Additives that have been effective in some studies
such as niacin (vitamin B3), fat-soluble vitamins (A, D,
and E), probiotics containing Aspergillus oryzae, dried
brewer’s yeast and yeast cultures, live cell yeast or
essential oil extracts can also be used to alleviate the
effects of heat stress.
Beating the heat
Nutritionists can formulate feed to decrease the
effect of heat stress on animals but this is only a tool
dairy farmers can use together with good management practices. Some of these practices include
providing most of the ration during the cooler
periods of the day to minimise heat production at
higher temperatures. Other practices include providing shade and extra air movement, and supplying
clean and abundant drinking water. Based on this
data, the recommended concentration of potassium in lactating dairy cows should be between 1,1
and 1,5% during heat stress to improve feed intake
and to maintain a good electrolyte balance in the
cow. Work with your nutritionist to ensure that the
ration delivers the nutrients needed for peak performance in hot weather and put
some management practices
in place to decrease the effect
of heat stress on your animals.
Anelle Wabeke is a nutritionist specialising in ruminant nutrition at ADVIT
Animal Nutrition. Contact her at [email protected] for more information. TDM
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