The first point that needs to be made is that trace mineral salt is not a complete mineral, it contains no calcium or phosphorus. When evaluating the composition tag on a bag of minerals look for the following: 15 to 30% salt, 6 to 12% calcium, 6 to 12% phosphorus, 1 to 4% magnesium (8-14% for hi-mag in the spring), .09 to .18% copper, .18 to .36% zinc and .0026 to .0052% selenium. If concentrations of these minerals are considerably outside of these ranges, look for another. Consumption levels should be between 2 and 4 ounces per day. There will be extreme differences in prices, make sure that you consider composition and daily intake when evaluating these price differences - the least expensive bag is not necessarily the best buy! Some minerals will contain only 1% phosphorus, this is not enough unless the cows are fed broiler litter or the pastures are constantly fertilized with litter, which contains abundant amounts of phosphorus and other minerals.
Other points to ponder:
1. If the cows routinely run out of mineral then consumption levels will not be in the 2 to 4 ounce range - it is important to have mineral available at all times.
2. If abundant quantities of litter are being fed then mineral consumption will nearly cease.
3. If you feed a "hot mix" during the winter (e.g., cottonseed meal and salt) then special care will need to be taken to ensure adequate trace mineral, calcium and phosphorus consumption is achieved.
4. A good homemade recipe that will work is to mix a 50-pound sack of trace mineral salt with a 50-pound sack of dicalcium phosphate and feed this free-choice.
5. High-Mag mineral does not need to be fed
all year, the most critical time is during the spring. Complete details
on this topic can be found here: grass