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Should we be adding trace minerals to the TMR?

Gerald E. Higginbotham and Jerry Spears Published on 30 September 2015
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Rumen micro-organisms require trace minerals for proper function. However, most research has shown micro-organism requirements for copper, manganese and zinc are minor and much lower than those typically provided by ruminant diets.

Nevertheless, studies that use laboratory procedures to simulate the rumen environment suggest relatively small concentrations of copper, manganese and zinc can impact fiber digestion.

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The results from these studies suggest rumen microbes can maintain proper function using trace minerals found naturally in feedstuffs without additional supplementation.

Rumen micro-organisms need a soluble source of the trace mineral cobalt. Cobalt is required for rumen micro-organisms to synthesize vitamin B12, which is required by all cattle.

In addition to being required by cattle, vitamin B12 is required by some rumen bacteria for their normal metabolism. Some rumen bacteria cannot synthesize vitamin B12 and depend on other bacteria present in the rumen to produce vitamin B12 for their needs. A deficiency of soluble cobalt in the rumen can impair rumen fermentation.

Conversely, excessive supplementation of trace minerals may create a rumen environment with trace mineral concentrations well in excess of microbial needs, perhaps impacting their ability to function.

The solubility of trace minerals can differ depending on the source, and it is assumed that only minerals soluble in the rumen will be available to the rumen bacteria for their use.

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Behavior of sulfate and hydroxy trace minerals in the rumen

Sulfate trace minerals are readily soluble in water and in the rumen environment. After becoming soluble in the rumen, sulfate forms of trace minerals would be highly susceptible to various interactions with rumen micro-organisms and the many common trace mineral antagonists found in the rumen.

Hydroxy trace minerals are relatively insoluble in water or the rumen environment but become soluble under acidic conditions typical of those found in the abomasum and lower digestive tract of cattle.

Researchers Genther and Hansen (2015) reported rumen-soluble concentrations of copper and manganese were lower in cattle supplemented with hydroxy forms of trace minerals compared to cattle supplemented with sulfate forms.

In this study, soluble concentrations of zinc in the rumen were higher in cattle supplemented with hydroxy zinc versus zinc sulfate. It is unclear why soluble zinc levels were greater in cattle receiving zinc hydroxychloride.

Prior research, along with a recent study at Colorado State University (Caldera, et. al, unpublished) compared rumen-soluble concentrations of zinc after dosing rumen-fistulated steers with zinc sulfate or zinc hydroxychloride.

Following dosing, rumen-soluble zinc concentrations increased greatly in steers given zinc sulfate – but not in those receiving zinc hydroxychloride.

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Why it matters

A recent study published in the Journal of Dairy Science (Genther and Hansen) compared the impact of trace mineral source (sulfate versus hydroxy forms) and level on dry matter and neutral detergent fiber digestion in cattle.

Rumen-fistulated steers were fed a corn silage-based diet formulated to meet the needs of a high-producing dairy cow.

Treatments consisted of the control TMR with no supplemental zinc, copper and manganese, or the control TMR supplemented with low (30 ppm zinc, 5 ppm copper, 15 ppm manganese) or high (120 ppm zinc, 25 ppm copper, 60 ppm manganese) trace mineral concentrations from either sulfates or hydroxyl minerals.

The control diet was below the NRC requirement for copper and zinc for lactating dairy cows.

After allowing steers 10 days to adapt to their diet, Dacron bags containing ground samples of the control TMR were inserted into the rumen for various times (six, 12, 24 or 36 hours). The pore size of Dacron bags allow rumen micro-organisms to freely enter the bag and digest the diet.

However, portions of TMR were not able to exit the bag unless they had been digested. Since the control TMR was placed in all Dacron bags, treatment effects on rumen digestion are due to the different trace mineral sources or levels affecting the ability of the rumen micro-organisms to digest the TMR feed.

Supplementation of trace minerals to the control TMR did not increase disappearance (digestion) of dry matter or neutral detergent fiber from the Dacron bags.

This indicates the zinc, copper and manganese provided from the control TMR was sufficient to maximize rumen fermentation. These results agree with a recent study (Dermauw, et. al, published in Livestock Science) where trace mineral supplementation did not affect digestion in cattle fed grass.

The addition of sulfate forms of zinc, copper and manganese to the control TMR reduced (P=0.03) dry matter disappearance. Supplementation with hydroxy forms of zinc, copper and manganese did not affect dry matter disappearance (P=0.18). Neutral detergent fiber disappearance from Dacron bags was not affected by trace mineral source or concentration.

Summary

Iron, zinc, cobalt and manganese are required in small amounts by rumen micro-organisms. Low cobalt levels in feedstuffs can reduce rumen propionate production and decrease fiber digestion.

Providing a supplemental source of cobalt that is available to rumen micro-organisms is important in order to maximize rumen fermentation and also to ensure that rumen bacteria synthesize sufficient vitamin B12 for the host animal.

Trace minerals requirements of the host ruminant are considerably higher than those needed for optimal rumen fermentation by the micro-organisms. There is no evidence that zinc, manganese or copper levels in practical cattle diets enhances rumen fermentation.

Therefore, the choice of a supplemental source of these minerals should be based on bioavailability to the animal rather than availability to rumen micro-organisms. High rumen fluid concentrations of zinc, copper and iron can be toxic to some rumen micro-organisms and thus impair rumen fermentation.  PD

Jerry Spears is with the Department of Animal Science, North Carolina State University – Raleigh.

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

Gerald E. Higginbotham
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