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The unseen but vocal components of forages

John Goeser and Dustin Sawyer for Progressive Forage Published on 30 September 2016

When discussing forage quality, we often focus on carbohydrates and the energy derived from these forage nutrients. Carbohydrates account for half to three-quarters of a feed’s weight, deliver the majority of the energy and, in turn, drive milk production, health and performance.

There is another component to forage, in parts per million (ppm) quantities, which is often overlooked or even ignored. To what are we referring? Trace minerals and metals.

The ppm fraction consists of aluminum, boron, cobalt, copper, iron, manganese, molybdenum, selenium and zinc, among others. Cobalt, copper, iron, manganese, molybdenum, selenium and zinc are important for animal nutrition but can also cause toxicity within dairy cattle.

After being absorbed, these trace minerals are co-factors and part of countless vital biological pathways and metabolism, such as transporting oxygen within the body, helping with immune and tissue function, and affecting hoof integrity.

Plants also need trace minerals for biological functions and growth. Plants uptake available minerals from the soil depending on a number of factors, including but not limited to soil pH, organic matter and water content.

For animals, absorption of trace minerals also varies and is dependent on several factors. Because of variable absorption, and an understanding that trace minerals are vital and important to nutrition and health, nutritionists tend to supplement these with both organic (more readily absorbed) and inorganic (less readily absorbed, for example, copper sulfate) forms to meet nutritional needs.

Requirements and supplementation guidelines have been evolving over the past 15 years as the National Research Council convenes again and research further helps nutrition experts understand optimal supplemental levels.

In general, forage trace mineral content, variation in farm-grown feeds and non-supplement contributions to the diet are relatively poorly understood, so the industry often relies on feed library base values.

To evaluate forage trace mineral potential impact on animal nutrition, we queried 2012 to 2016 soil and forage trace mineral analysis data and summarized results by year.

We evaluated variation and season trends for only the upper Midwestern U.S. due to the fact that soil measures for our facility are largely from this region. Figures 1 through 4 demonstrate both soil and forage trace mineral trends for the upper Midwest for 2012 through 2016.

The unseen but bocal components of forages

Copper content in forages has become a focus for some, with recognition that copper content in dairy diets may be additively stored within the liver as cows mature. How has soil and forage copper content trended the past few years? Interestingly, soil and forage moved in different patterns.

Soil copper content trended lower in 2012 but has been relatively constant on average for the years since. The standard deviation around the average has also been relatively constant for the past four years, with samples deviating 100 percent from the average.

This can be practically interpreted to mean that soil copper levels could be near zero or could be as high as 5 ppm. Forage copper content also varied considerably within each year, but the peak forage copper was observed in 2014, not in 2012 like soil.

Interestingly, manganese, iron and zinc soil and forage contents all appeared curiously disconnected from one another. For reasons we can only speculate for this article, these trace minerals demonstrated 50 to 100 percent changes in year-to-year averages and also considerable variation in samples within a given calendar year. So what’s the bottom line? Forage trace mineral content also varies, markedly.

Dietary copper content was surprisingly consistent across years. Conversely, TMR iron, manganese and zinc concentrations differed by somewhere between 15 and roughly 60 percent from one year to another.

What causes forages to differ in trace mineral content within a field from year to year? The year-to-year variance can be largely isolated to environmental conditions throughout the growing season, most notably rainfall. Within a year, soil trace mineral availability for plant uptake is highly dependent on soil pH and organic matter content.

All things considered, soil mineral content may be well beyond adequate; however, the minerals may not be available, and thus the plant could be deficient.

At the end of the day, are these year-to-year soil or TMR differences real and meaningful? That answer is up for debate. We strongly suggest you engage your nutritionist, agronomist and consulting team and start a discussion on this topic. Test your soil and forages for trace mineral content periodically and incorporate this information into your plant and animal nutrition management efforts.

Remember, parts per million is a very small amount, but better understanding these quantities can help your dairy improve health and performance.  end mark

Dustin Sawyer, M.Sc., is also with Rock River Laboratories. Email Dustin Sawyer.  

John Goeser
  • John Goeser

  • Director of Nutrition - Research and Innovation
  • Rock River Lab Inc.
  • Email John Goeser