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Tracing chromium concentrations in ruminant feeds

Jerry W. Spears for Progressive Forage Published on 28 September 2017
Loose forms of byproducts

Providing adequate trace minerals to dairy cows is essential for high production and good health.

Minerals required by cattle, in microgram or milligram amounts per day for optimal nutrition and performance, are called trace minerals. The nine trace minerals considered essential for cattle are:

  • Chromium (Cr)
  • Iron (Fe)
  • Zinc (Zn)
  • Copper (Cu)
  • Manganese (Mn)
  • Selenium (Se)
  • Cobalt (Co)
  • Molybdenum (Mo)
  • Iodine (I)

Unfortunately, quantifying the supply of available trace minerals and their requirements is extremely difficult, which leads to a high degree of uncertainty relative to
diet supplementation.

Chromium

Chromium (Cr) potentiates the action of insulin in insulin-sensitive tissues. This allows for optimized glucose utilization, which can result in better animal maintenance, reproduction, growth and immunity. Recent studies have indicated that chromium propionate (Cr Prop) supplementation may enhance performance and health of stressed calves and increase milk production in dairy cows.

Subsequent research demonstrated that Cr supplementation during late gestation and early lactation increased milk production in dairy cows. The U.S. Food and Drug Administration Center for Veterinary Medicine issued a regulatory discretion letter in 2009, which permitted the use of Cr Prop as a source of Cr for supplementation to cattle diets at levels up to 0.5 mg of Cr per kg of dry matter (DM).

Little is known regarding Cr concentrations naturally present in practical feedstuffs. Chromium analysis of feed ingredients and total diets is challenging because of the low concentration of Cr normally present and problems with Cr contamination of samples during collection, processing and laboratory preparation of samples for analysis.

A recent study conducted at North Carolina University (NCSU) set out to determine the Cr concentrations in feed ingredients commonly fed to ruminants and to determine the extent of variation that exists within several feed ingredients derived from different geographic areas throughout the U.S. Feed ingredients were collected from dairy farms, feed mills, grain bins and research farms at NCSU and Michigan State University.

Chromium concentrations in concentrate feeds

Mean Cr concentrations in whole cereal grains were low, ranging from 0.025 mg per kg of DM for oats to 0.041 mg per kg DM for wheat. Processed (cracked or flaked) corn samples received and then ground through a stainless steel screen had Cr concentrations almost twice as high as those in whole corn samples (Table 1).

Chromium concentrations (mg/kg DM) in concentrate feeds

Whole cottonseed and soybeans had slightly greater Cr concentrations than the cereal grains. Soybean meal samples contained the greatest Cr concentrations of the concentrate feeds evaluated in this study.

Chromium concentration in forages

Harvested forages contained greater Cr concentrations than concentrates (Table 2).

Chromium concentration (mg/kg DM) in forages

Alfalfa hay or haylage (0.522 mg of Cr per kg of DM) contained greater mean Cr concentrations than corn silage (0.220 mg per kg of DM) or grass hay (0.155 mg per kg of DM).

Chromium concentrations in byproduct and miscellaneous feeds

Chromium concentrations in byproduct and miscellaneous feed ingredients are shown in Table 3. Beet pulp (mean equals 1.222 mg per kg of DM) and corn steep liquid (1.053 mg per kg of DM) contained the greatest Cr concentrations of the byproduct feed ingredients analyzed.

Chromium concentrations (mg/kg DM) in byproduct and miscellaneous feeds

The greater Cr concentrations in beet pulp may be due to greater soil contamination because beets grow underground. With the exception of beet pulp and corn steep liquid, other byproduct feed ingredients averaged less than 0.60 mg of Cr per kg of DM.

Pelleted samples of soybean hulls had greater Cr concentrations than samples of soybean hulls received in a loose form. The greater Cr concentration in pelleted samples may be due to Cr contamination occurring during pelleting or during grinding of pelleted samples in the laboratory.

Pelleted samples were ground through a stainless steel screen, but loose samples were not. Byproduct feed ingredients generally contained greater Cr concentrations than the whole grains analyzed.

Analyzing for chromium content

Accurately measuring naturally occurring Cr in feed ingredients is difficult because of Cr contamination that can occur during harvesting, processing and collection of samples, as well as laboratory analysis of Cr. Chromium is ubiquitous in nature, occurring in soils, plants, water and air.

Chromium is also used as a component of chrome and in chrome plating, leather tanning and the manufacturing of pigments and wood preservatives. Soil contamination can also contribute to the total Cr concentration in feed ingredients and feeds.

Analytical determination of Cr also represents another source of variability and error in accurately reporting Cr concentrations in feed ingredients because of the low Cr concentrations present and Cr contamination from reagents used in preparation of samples for analysis.

Conclusion

Chromium concentrations in most ruminant feedstuffs and feed ingredients are low. Studies in humans and rats have indicated that the bioavailability of Cr naturally present in foods is low. Animal feed ingredients would consist of a combination of Cr naturally occurring in feeds and Cr resulting as a contaminant from soil, metal contact, or both. Chromium in soil and from metal contamination during harvesting or processing is probably unavailable or at least of extremely low bioavailability to ruminants.

Mean Cr concentrations in unprocessed cereal grains are less than 0.05 mg per kg of DM. Harvested forages contained greater Cr concentrations than grains, with mean Cr concentrations ranging from 0.155 mg per kg for grass hay to 0.522 mg per kg for alfalfa hay or haylage. Byproduct feed ingredients ranged from 0.040 mg per kg for cottonseed hulls to 1.222 mg per kg for beet pulp.

Grinding whole grain samples through a stainless steel Wiley (Arthur H. Thomas Company) mill screen greatly increased analyzed Cr concentrations. Much of the analyzed total Cr in feed ingredients appears to be due to Cr contamination from soil or metal contact during harvesting, processing, or both. This study indicates that the permitted concentration (0.50 mg of Cr per kg of DM) of Cr Prop that can be supplemented to cattle diets is significant with regard to total dietary Cr intake.  end mark

PHOTO: Loose forms of byproducts (such as dried distillers grains) had lower levels of chromium concentrations compared to pelleted byproducts, likely due to less contact with processing equipment. Photo by Lynn Jaynes.

References omitted but are available upon request. Click here to email an editor.

Jerry W. Spears
  • Jerry W. Spears

  • Professor Emeritus of Animal Science
  • North Carolina State University
  • Email Jerry W. Spears

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