What Needs to Be in Your Free-Choice Mineral Supplement When Grazing Cereal Rye or Other Small Cereals?

By Mary Drewnoski

Cereal rye, winter wheat, and winter triticale grown on the same soil will have a similar mineral profile. For both lactating cows and growing cattle (developing heifers and yearlings), the main mineral concerns with these forages are deficiencies in sodium, calcium, and magnesium. Additionally, young small grains tend to have high potassium levels, which interfere with magnesium absorption. This increases the need for additional magnesium supplementation, particularly for lactating cows, where the primary risk is tetany—a condition that can result in sudden death with little warning.

Mineral Supplementation for Lactating Cows

Tetany is caused by low blood magnesium and calcium. Since symptoms often go unseen until it’s too late, prevention is crucial. A properly formulated 4 oz free-choice mineral should include:

• Salt (NaCl): 20–25%
• Calcium (Ca): At least 8%
• Magnesium (Mg): At least 10%

Providing a mineral supplement with these levels will help meet the needs of lactating cows and reduce the risk of tetany.

Mineral Supplementation for Growing Cattle

While growing cattle are not as susceptible to tetany, supplementing calcium and magnesium has been shown to improve gains. Studies have reported weight gain responses of up to 0.5 lb/day in supplemented cattle compared to those without access to free-choice mineral. Additionally, magnesium supplementation may help reduce the risk of bloat by improving rumen motility, which aids in gas escape.

A 4 oz free-choice mineral for growing cattle should include:

• Salt (NaCl): 20–25%
• Calcium (Ca): At least 20% (higher than lactating cows due to increased growth demands)
• Magnesium (Mg): At least 5%

Additional Considerations

Ionophores (Monensin): Adding an ionophore, such as monensin, to a free-choice mineral supplement has been shown to improve gains of growing cattle. Responses of 0.20 lb/day have been observed with the cost of the product being far less than the value of gain.

Trace Minerals (Copper & Zinc): While these may have a less immediate effect, ensuring adequate copper (Cu) and zinc (Zn) levels is important for long-term health and immune function. 

A 4 oz mineral supplement should contain:

• Copper (Cu): 1,300–2,000 ppm
• Zinc (Zn): 2,000–3,000 ppm

Conclusion

Proper mineral supplementation is critical when grazing cereal rye or other small cereals. For lactating cows, ensuring adequate magnesium and calcium can prevent grass tetany. For growing cattle, supplementing calcium and magnesium can improve gains and potentially reduce bloat risk. Adding monensin can further enhance growth performance, and including copper and zinc will help meet essential trace mineral needs. By providing a well-balanced free-choice mineral, producers can maximize cattle health and performance while grazing small cereals.