The
more intensive system of farming with the objective of raising the milk
production has increased
the stress factors on the dairy cows. The transition period of late gestation
through early lactation
is a particularly crucial time for high producing dairy cows and during this
period the cows are under great physical, nutritional and metabolic stresses
which are reflected in altered hormone profiles and increased disease or
disorder susceptibility. During this period high yielding animals are in a
negative energy balance and they require a large amount and rapid supply of
glucose for milk lactose synthesis which results in lower plasma glucose and
insulin, compared with later in lactation. The ability of insulin to control
glucose utilization and partitioning determines milk production, fertility and
health status of cows.
THE
ROLE OF CHROMIUM
Chromium
is an integral component of the Glucose Tolerance Factor (GTF) which is an organometallic
molecule potentiating the effect of insulin binding to receptors at the cell
surface. With chromium acting as a cofactor of insulin, it is required for
normal functioning of the B cells in the pancreas, preventing hyper
responsiveness of insulin secretion to glucose stimulation. Glucose Tolerance Factor
was first isolated from pork kidney and brewer's yeast and it has a much
greater biological activity than do inorganic sources of chromium alone.
Glucose Tolerance Factor consists of chromium (Cr+3),
organic components of nicotinic acid, glycine, glutamic acid and cysteine and
without chromium at its core it is inactive.Chromium in plants is organically
complexed with concentrations approximating 30 to 50 ppb reported in very
limitedstudies.
Good natural sources, in addition to brewer's yeast, include dark chocolate,
black pepper and some processed meats. Higher concentrations of total chromium
in diets would probably be due to contamination in feedstuffs, particularly
forages, or high contamination in mineral supplements. Circulating chromium is
associated with the Bglobulin portions of plasma and in physiologic concentrations
is transported to tissues bound to transferrin and possibly as a component of
GTF. Unlike elements such as calcium and magnesium there is no equilibrium between
tissue stores of chromium and plasma. Absorbed chromium is mainly excreted in
the urine.
Small amounts, however, are lost in perspiration, milk and bile. Inorganic
chromium is very poorly absorbed within a range of 0.4 to 2 % while the
availability of organic chromium is more than 10 times higher. Also the
inorganic chromium must be converted to an organic complex,
such as GTF to enable the physiological functioning of chromium. Conversion of
inorganic chromium in the liver or kidneys to the bioactive form may be slow
and therefore supplying chromium in the preformed organic complex form
increases absorption reduces
variability in responses and negates the need for adequate dietary precursors
like nicotinic acid, certain amino acids to aid inorganic chromium absorption
andconversion
to the bioactive form. Chromium supplementation of cattle diets has affected
carbohydrate and lipid metabolism in a number of studies using various forms of
supplemental chromium which include chromium chloride, chromium tripicolinate,
chromium nicotinic acid complex, chromium amino acid chelate, chromium propionate
and high chromium yeast. The variation in responses observed between different
studies may reflect differences in the bioavailability of these supplemental
chromium sources and bioavailability of chromium in the control diet. Supplemental
organic chromium can increase the rate of gain anywhere from 0 to 30 per cent depending
upon the level of stress or disease challenge. However, chromium does not
actually increase the rate of gain; rather it prevents the depression in rate
of gain which often occurs under stressful or other conditions leading to
chromium deficiency. To be fully effective,supplementation
at an adequate level must begin early in the disease challenge or stress
period.Supplemental
organic chromium may be needed or economically beneficial in the following circumstances:
- During heat stress periods.
- With poorly managed animals subject to more pathogenic, environmental and even
nutritional stress.
- In borderline or lower protein diets.
- Rations containing high level of silages particularly legume silages which have
excess non protein
nitrogenous substances or soluble nitrogen leading to stress due to nutritional
imbalance.
- In low effective fibre diets.
Fineness
of silage or hay chop and level or type of non-structural carbohydrates have a
major effect on rumen propionate, which may lead to mobilization of chromium
from body stores and probably increase urinary chromium excretion. Another nutritional
factor that may influence chromium depletion in ruminants is hyperammonemia or
elevated blood ammonia concentration.
Chromium
seemed to reduce blood cortisol concentrations during stress and promoted
improved insulin
or insulin like growth factor (IGF-1) sensitivity in target tissues such as
muscle, mammary gland and the immune system. Supplemental organic chromium is
found to improve the milk production of young dairy cattle during stress
periods, reduce age related metabolic disorders like ketosis and also decrease the
incidence of milk fever, retained placenta and even acidosis.
CONCLUSION
Organic
chromium supplementation in the concentrate mixture improves the dry matter
intake,total milk production and
help to maintain the peak yield as well as persistency of milk production in early
lactating crossbred cows. The postpartum reproductive performance will also be
influenced favorably by the supplementation of organic chromium in crossbred
cows
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