Minerals and Vitamins
The next section is vitamins and minerals. Dairy cows have a requirement
both for macrominerals and microminerals. Macrominerals are expressed
in grams per day or as a percent dry matter. Dairy cows have a requirement
for calcium and phosphorus, magnesium, potassium, sodium, chlorine and
sulfur. For the trace minerals, these are fed at milligrams per day or
as a concentration, milligrams per kilograms of dry matter or parts per
million. Dairy cows have a requirement for the following trace minerals
or microminerals: cobalt, copper, iron, iodine, manganese, selenium and
zinc. We will just briefly talk about some of the concerns with some minerals.
We will talk about the calcium to phosphorus ratio, which is actually
very important in growing animals and it should be maintained at some
ratio of about two to one calcium to phosphorus. For lactating animals,
we found that it really does not matter what the ratio is, as long as
calcium and phosphorus are sufficient in the diet. Phosphorus is becoming
more of a concern as a pollutant to the environment. We never want to
overfeed phosphorus in dairy diets.
The electrolytes, sodium, chlorine and potassium, can become important
in heat stress or if animals are in a heat stress environment. We can
actually increase production if we increase these three minerals in the
diet. Potassium can cause milk fever in cows near parturition or dry cows/pregnant
cows that are near parturition that are consuming high potassium forages
are at increased risk for milk fever at calving.
Magnesium can turn into grass tetany if there is a deficiency. Most often
we see grass tetany on animals grazing lush pastures in the spring. Usually,
if we are grazing lush pastures in the spring, with dairy cows, we will
usually increase the magnesium concentration in the diet.
The next table depicts the concentrations of the macrominerals for different
levels of milk production for your reference.
Dietary Mineral Concentrations
Milk |
Ca |
P |
Na |
Cl |
K |
Mg |
S |
lb/d |
% of
Diet DM |
100 |
0.60 |
0.37 |
0.21 |
0.26 |
1.04 |
0.19 |
0.20 |
75 |
0.56 |
0.34 |
0.21 |
0.24 |
1.02 |
0.18 |
0.20 |
50 |
0.52 |
0.31 |
0.22 |
0.22 |
1.00 |
0.16 |
0.20 |
The next table shows the concentration of trace minerals that should be
in dairy diets.
Trace Minerals Requirements
Micromineral
|
PPM |
Co |
0.11 |
Cu |
15 |
I |
0.5 |
Fe |
15 |
Mn |
15 |
Se |
0.3 |
Zn |
60 |
What about feeding minerals to animals? There are several different choices.
The preferred choice is force feeding or mixing in either a TMR or in
a grain mix. You can also provide minerals free choice, this is also known
as cafeteria style. We simply supply unmixed supplements of dical, salt,
limestone, etc. to dairy cows. But research has shown that cows cannot
determine when they need limestone or calcium or when they need dical,
which is calcium and phosphorus. The only mineral that should be supplied
free choice, that animals physiologically they know when they need it,
would be salt.
The fat soluble vitamins or A, D, E are required to be supplemented in
dairy diets. However, the B vitamins are usually produced in a sufficient
quantity in the rumen that we do not need to supplement for these.
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