It’s now July and you may notice that the current daily temperatures are not what you were expecting. Truth be told, if you look through NASA’s data, it’s been getting hotter and hotter in July since the 1800s. Currently, we are in year five of the hottest on record since 2005.

Are you prepared to supplement your cattle’s mineral needs for a potential sixth year of record-breaking heat? Have you adjusted your mineral ration yet for the type and stage of lactation of the cattle you are feeding now? Do you know for sure what their basic needs are? Or why trace minerals are so important?

Let’s look at the evolution of the science behind what we know today about livestock nutrition.

The U.S. heyday era

In 1880, Henry Prentiss Armsby, an agriculture chemistry professor, published a book, “Manual of Cattle Feeding.” Six years later, as associate director and chemist of the Agricultural Experiment Station at the University of Wisconsin, he presented a paper to the Wisconsin Dairymen’s Association, “Does rich food enrich the cow’s milk?” The answer was yes, richer feeds produced richer milk.

If Armsby is the godfather of animal nutrition, surely to many a college student, Frank B. Morrison is the father of feeds and feeding. Morrison was director of the Cornell Agricultural Experiment Station in Geneva, New York, in 1927, and later an animal nutrition professor at Cornell University. His first edition on the subject of animal feeds and feeding was published in 1898.

Modern times

By the 1930s, research specifically related to livestock mineral needs was well under way. The U.S. Department of Agriculture published “The composition of the principal feedstuffs used for livestock” in 1939 and another pamphlet on “The nutritional diseases of farm animals” in 1942. Land grant university research on livestock nutrition was also in full swing by the 1960s.

The cumulative work of hundreds of scientists and thousands of studies identified the importance of minerals – calcium, phosphorus, salt, sodium, potassium, magnesium, copper, selenium, zinc, manganese, iodine, cobalt, molybdenum, sulfate, fluorine and vitamins A, B complex, D and E – in beef and dairy cattle nutrition.

What has changed?

Cattle frame scores, feed conversion to milk yield per cow genetics, capitalism in milk and meat production and aggressive marketing and advertising of how to maximize margins have exponentially increased the information the average producer receives on livestock nutrition. Another significant shift is the availability and abundance of supplemental feed choices.

Currently 1,618 U.S. firms are registered as manufacturers of livestock feed. Livestock mineral and feed manufacturing is a global market and only four of the top 20 leading feed producers are in the United States, according to WATT Ag Net, a website providing information on global poultry, pig and animal feed manufacturers.

Sometimes it’s hard to make sense of all the scientific jargon and recommendations and comprehending what the National Research Council tables mean. All you want to know is what they need, right? The guaranteed analysis tag on your bag of beef mineral supplement can help you figure that out.


Ninety-nine percent of the calcium a cow needs is stored in her bones. If a cow or calf lacks calcium you’ll notice a decrease in weight gain or a decrease in efficiency of gain. Calcium levels are tied to phosphorus levels and the two nutrients must be kept in sync. This is where “balancing a ration” comes into play. If your soil tests and pasture forage analysis indicate calcium is inadequate or deficient the percent calcium on the mineral mix label becomes critical in choosing an optimal mineral pack to restore those reserves. Lactation is a huge draw on calcium reserves. The nutrient requirements of beef cows are highest approximately two months after calving when cows reach peak lactation.


Phosphorus is essential to creating and using energy. It is also stored in the bones along with calcium. Again, the ratio to calcium is important. For a mature beef cow, an adequate dry matter calcium percent is as follows: phosphorus percent ratio in consumed feed can range from 2:1 to 7:1. You could just as easily be oversupplying as undersupplying these two essential ingredients to your cattle. To know for sure, evaluate where these levels are in your herd at different stages of lactation or reproduction; at different times in the forage cycle of the year; and when weather conditions change.

When was the last time you:

  1. Soil tested your pastures and tested your stored forages to learn the calcium-to-phosphorus ratio?
  2. Tested the amount of excreted P in manure – too much? Too little?
  3. Tested the surface water quality of your cattle’s drinking water for excessive P? In the heat of summer, pond scum in high P stagnant water can be deadly.

Although it is true that phosphorus, nitrogen, potassium and magnesium are very mobile in plants and excess comes out in the urine and manure, it’s important to note that they are also fairly immobile in the soil. It might be out there already, and you might have spread it out there just now in the form of manure or purchased fertilizer, but ultimately it might not be readily available for plant uptake. Also of note, calcium, sulfur, boron, copper, iron, manganese, and zinc are immobile nutrients, which means they tend to accumulate in the portions of the grass sward your cows don’t want to eat in the heat of summer.

Salts and sodium

As temperatures go up, so does the critical daily need for salt in any living thing’s diet. Cows don’t retain sodium and chlorine like they do calcium. They use it as fast as they consume it to regulate and retain water. Remember, water intake doubles in the heat of summer.

Expect your adult cattle will consume 1 to 2 ounces of salt a day (0.005 to 0.010 percent of their body weight), if not more, as the summer heat progresses. Don’t estimate. Calculate ounces per head for your herd per day. You might be surprised how often you underestimate your herd’s need for salt replenishment.

The format of these non-pet food labels is provided by the Association of American Feed Control Officials. These standards require ingredients to be listed in the following order. Ingredients numbers 7 through 12 are the mineral and vitamin content.

  1. Crude protein (min.)
  2. Equivalent crude protein from nonprotein nitrogen (NPN) (max.)
  3. Amino acids (min.)
  4. Crude fat (min.)
  5. Crude fiber (max.)
  6. Acid detergent fiber (max.)
  7. Calcium (min.) and (max.)
  8. Phosphorus (min.)
  9. Salt (min.) and (max.)
  10. Sodium (min.) and (max.)
  11. Other minerals guarantees (min.), if a requirement of a specific specie feed (grouped by units of measure).
  12. Vitamins (min.)
  13. Total sugar as invert (min.)
  14. Viable microorganisms producing lactic acid (min.)
  15. Other guarantees (min.)

If your livestock is not foraging for themselves and seeking out what they need, they are limited to consuming feeds harvested or purchased. It’s up to you to ensure they are getting a balanced ration of essential minerals and vitamins.

Other mineral guarantees

By mid-summer, potassium and magnesium are usually not a concern unless you are turning cattle out on high potassium forages or your cattle are in high lactation mode. Keep track of where you spread potash or chicken manure if you decide to graze these forages. Supplemental magnesium is needed on high potassium forages. Don’t forget there is a maximum tolerable level in cattle rations for magnesium (0.40 percent), potassium (3.0 percent), and sulfur (0.4 percent), which varies by animal age, weight and stage of lactation. Keep that in mind if you are turning cattle out or are feeding forages from where you limed recently with high MAG, or spread fertilizers containing these ingredients, and also are putting out a salt mineral mix containing high amounts of these minerals.

Sulfur toxicity is becoming more common. Test surface waters and feed rations for too much sulfur.

Micronutrients and trace minerals

If micronutrients are present in manufactured feed or mineral mix, they will be listed on the label. Before you guess what, if any, micronutrients like copper, selenium, sulfate, zinc, manganese and cobalt you need, make sure you actually have a deficiency. These nutrients are needed in small amounts and the difference between under-supplied and over-supplied could be a death sentence. Too little equals a very sick animal; too much equals a very sick animal. Soil tests, forage analysis, and blood tests can be used to determine the need for these trace minerals.


Most cattle on pasture can synthesize enough vitamins from the sun and forages to maintain optimum levels. However, a soil selenium deficiency can ultimately interfere with vitamin E synthesis and all barn-kept cattle are at risk to be deficient in vitamin A if they only consume stored feeds. Stored feeds leach vitamin A over time. Other trace vitamins that sunlight-deficient cattle may need include B12, thiamine, biotin and riboflavin.

Reference: Nutritional Requirements of Domestic Animals. Publication 579. National Academy of Sciences. 1958.