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Minerals for Dairy Cattle - Guide D-205 of the Cooperative Extension Service

Recommended mineral content of rations for dairy cattle
Minerals
High
producing
cows
Dry
pregnant
cows
Mature
Bulls
Growing
cattle
Calf starter
concentrate
mix
Calf
milk
replacer
Maximum
concentration
for cattle1
Calcium, %
0.60
0.37
0.24
0.40
0.60
0.70
--
Phosphorus, %
0.40
0.26
0.18
0.26
0.42
0.50
--
Magnesium, %2
0.20
0.16
0.16
0.16
0.07
0.07
--
Potassium, %3
0.80
0.80
0.80
0.80
0.80
0.80
--
Sodium, %
0.18
0.10
0.10
0.10
0.10
0.10
--
Salt, %4
0.46
0.25
0.25
0.25
0.25
0.25
5
Sulfur, %
0.20
0.17
0.11
0.16
0.21
0.29
0.35
Iron, ppm5
50.0
50.0
50.0
50.0
100.0
100.0
1,000
Cobalt, ppm
0.10
0.10
0.10
0.10
0.10
0.10
10
Copper, ppm
10.0
10.0
10.0
10.0
10.0
10.0
80
Manganese, ppm
40.0
40.0
40.0
40.0
40.0
40.0
1,000
Zinc, ppm6
40.0
40.0
40.0
40.0
40.0
40.0
500
Iodine, ppm
0.50
0.50
0.25
0.25
0.25
0.25
50
Molybdenum, ppm7
--
--
--
--
--
--
6
Selenium, ppm
0.10
0.10
0.10
0.10
0.10
0.10
5
Fluorine, ppm7
--
--
--
--
--
--
30
  1. Maximum safe levels are not well defined for minerals, and estimates are given especially for S, NaCl, Fe, Cu, Zn, and Mn.
  2. Increase to 0.25 % or higher when conditions are conductive to grass tetany.
  3. See Guide D-205 for recent suggestions.
  4. Sodium chloride (NaCl).
  5. Maximum safe level depends upon chemical form.
  6. Maximum safe level for mature cattle is 1,000 ppm.
  7. Minimum requirements are not yet established.
Source:  National Research Council, 1978. Nutrient Requirements of Dairy Cattle, 5th ed.
 

Controlling Grass Tetany in Livestock - Guide B-809 of the Cooperative Extension Service

"Forage containing less than 0.2 percent magnesium (Mg) and more than 3 percent potassium (K) and 4 percent nitrogen (25 percent crude protein) are especially likely to cause tetany.  Forage that is high in potassium and nitrogen should also have at least 0.25 percent magnesium.  When an animal is on high nitrogen forage, the rumen produces a large amount of ammonia.  Under these conditions, dietary magnesium may be converted to the relatively insoluble hydroxide, thereby lowering availability to the animal's tissues."
 

Recommended mineral concentrations in rations for beef cattle (dry basis).1

Mineral
Growing steers and heifers
Dry cows
Lactating cows
Possible toxic levels
Calcium, %
0.22 - 1.532
0.16 - 0.273
0.27 - 0.584
2.00
Phosphorus, %
0.27 - 0.592
0.17 - 0.223
0.22 - 0.394
1.00
Requirement
             Mineral        
                Suggested value            
                    Range                  
Possible toxic levels
Magnesium, %
0.10
0.05 - 0.25
0.40
Potassium, %
0.65
0.50 - 0.70
3
Sodium, %
0.08
0.06 - 0.10
10
Sulfur, %
0.10
0.08 - 0.15
0.40
Iron, ppm
50
50 - 100
1000
Cobalt, ppm
0.10
0.07 - 0.11
5
Copper, ppm
8
4  - 10
115
Manganese, ppm
40
20 - 50
1000
Zinc, ppm
30
20 - 40
500
Iodine, ppm
0.5
0.20 - 2.0
50
Molybdenum, ppm
--
--
6
Selenium, ppm
0.20
0.05 - 0.30
2
Aluminum, ppm
--
--
1000
Lead, ppm
--
--
30.0
  1. National Research Council
  2. Amount of increase for smaller animals and with higher rates of gain.
  3. Amount of increase for larger animals and in the last third of pregnancy.
  4. Amount of increase for small animals and with increased milk production.