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Sulfate trace minerals: More harm than good, especially on fiber digestibility

Sara Kvidera and Michael Miller for Progressive Dairy Published on 11 December 2020

In the last few months, the dairy industry has seen significant swings in farmgate milk prices due to COVID-19 disrupting markets. A highly variable milk price puts tremendous pressure on maximizing income over feed cost (IOFC).

One of the most practical ways to reduce feed costs is to feed economical forages such as corn silage. When inclusion of corn silage increases in the diet, digestibility of fiber should be high in order to maintain (or potentially increase) intake and milk production.

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Brown midrib (BMR) corn has a gene mutation that increases fiber digestibility by reducing indigestible fiber in the plant. Previous research has shown that cows fed BMR corn silage have higher intakes and milk production than conventional varieties with less-digestible fiber. Clearly, it is important to minimize any adverse effects on fiber digestibility, especially in high-forage diets.

Trace minerals are among the smallest and least-considered components of the diet, but they are also one of the most important. Copper, zinc and manganese are essential to cow health and well-being due to their critical involvement in immunity, fertility and metabolism. However, not all trace mineral sources are equal. Some trace mineral sources can have unintentional consequences on aspects outside of trace mineral nutrition, such as fiber digestibility.

Sulfate trace minerals have weak ionic bonds that break easily in moist environments (such as the feed, mouth or rumen). This releases highly reactive free metal ions at liberty to interact with other nutrients or microbes in the rumen. Free metal ions have antimicrobial properties, which is why bond strength is so important; good bonds should release the metal at the right place in the digestive tract. Hydroxy trace minerals (IntelliBond) contain strong covalent bonds that protect the metal from being released too early in the feed or digestive tract, giving them an advantage in diet stability, palatability, fiber digestibility and trace mineral bioavailability over sulfate trace minerals.

Replacing sulfates with hydroxy trace minerals improves fiber digestibility in a wide variety of diet types (Figure 1); however, little work has been done with trace mineral source in conventional versus BMR corn silage diets.

A summary of studies examing the effect of replacing

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We recently evaluated corn silage and trace mineral sources on fiber digestibility at the W. H. Miner Institute in Chazy, New York. Cows were fed diets containing conventional or BMR corn silage with either sulfate or hydroxy trace mineral sources of copper, zinc and manganese. Supplemental trace mineral levels in the diet averaged 9.8 parts per million (ppm) copper, 63 ppm zinc and 41 ppm manganese across all treatments. As expected, BMR corn silage increased dry matter intake (DMI) (+1.3 pounds) and milk production (+5 pounds).

By replacing sulfate sources of copper, zinc and manganese with hydroxy trace mineral sources, neutral detergent fiber (NDF) digestibility was improved by two points. DMI was improved by 1.3 pounds per day when averaged across both diet types (Figure 2).

Effects of silage type and mineral source

The positive effect occurred regardless of corn silage type (no significant interactions). The difference in total tract digestibility of NDF partially accounted for the difference in DMI between sulfate and hydroxy trace mineral diets.

These results corroborate findings over the past five to six years, indicating that sulfate trace minerals have a negative impact on NDF digestibility across a variety of diet types, and replacing copper, zinc and manganese sulfate with hydroxy trace mineral sources mitigates this effect (Figure 1). On average, these research study diets contained supplemental copper, zinc and manganese at 12, 56 and 36 ppm, respectively. In our industry today, trace mineral levels are often much higher and can negatively affect fiber digestibility if from a sulfate source.

The primary goal of trace mineral supplementation is to meet the nutritional demands of today’s high-producing animals with a bioavailable mineral source that does its job without negatively interacting with other components of the diet and compromising rumen fermentation. Providing a high-quality, improved trace mineral source as a replacement for sulfate trace minerals ensures proper nutrition without the negative interactions sulfate minerals have on fiber digestibility. Is it time to re-evaluate your trace mineral source?  end mark

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PHOTO: Mike Dixon.

Michael Miller is a dairy nutrition consultant with Trouw Nutrition.

Sara Kvidera
  • Sara Kvidera

  • Technical Manager
  • Micronutrients USA LLC
  • Email Sara Kvidera

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