How much trace minerals do cows need? Trace mineral benefits for cattle are proven. Dairy cows need trace mineral supplementation to avoid mineral deficiencies in cattle that can have a negative impact lactational performance, health, and reproduction. Supplying dairy cows with trace minerals above recommended levels in the NASEM 2021 guidelines on the other hand can lead to:

• Increased feeding costs
• Increased reactivity towards vitamins in cattle supplements and premixes
• Antagonist effect with other minerals in the rumen
• Trace mineral toxicity in cattle
• Decreased dairy performance
• Soil contamination with trace metal ions

Trace mineral deficiencies in cattle are very uncommon nowadays, but studies in Canada¹ and the US² indicate that mineral supplementation in commercial dairies frequently exceeded the NASEM 2021 guidelines³. The recommendation for copper in the NASEM 2021 guidelines is to feed 10 ppm copper to a lactating cow producing 32 kg of milk. In the two studies cited above, average and median copper levels were 70–80% above this recommendation from the NASEM 2021 guidelines (see Table 1).

These findings suggest that over-supplementation of dairy herds with trace minerals above the NASEM 2021 recommendations is very common.

A UK study⁴ evaluated liver copper concentrations in 510 cull cows (see Figure 1). The results suggest that while copper deficiency symptoms in cattle are unlikely, the risk of copper toxicity in dairy cattle remains significant.

Similar trends were observed in studies looking at liver copper status of dairy cattle in the US⁵, and the Netherlands⁶:

• In the US study looking at trace mineral toxicity in cattle, 44% of liver samples had copper levels exceeding 500 ppm and 12% of liver samples had copper levels exceeding 850 ppm DM.
  
• In the study in the Netherlands, 10% of liver samples exceeded 1,066 ppm of copper.
  
  These studies confirm that, although copper deficiency symptoms in cattle are uncommon, over-supplementation of trace minerals above the NASEM 2021 guidelines remains a global concern, posing significant risks of mineral toxicity in cattle and mineral copper soil contamination.

Given the prevalence of trace mineral over-supply in dairy diets worldwide, a longitudinal study was conducted in the UK⁷ to examine the long-term effects of copper toxicity in dairy cattle. The study compared dairy heifers fed either a dietary copper level slightly above the NASEM recommendations (16 ppm DM) or an elevated level of copper in the diet (32 ppm DM). Diets were fed from 4 months of age until 6 weeks pre-calving. Results are shown in Figure 2.

Replacement heifers fed an elevated dietary copper level exhibited significantly higher hepatic copper concentrations at all time points compared to those fed slightly above recommended levels from the NASEM 2021 guidelines for cattle. Additionally, the elevated copper diet negatively affected fertility, with reduced conception rates at first service and an increased number of services required per pregnancy. These results show that trace minerals toxicity in cattle is a real risk if cattle are fed dietary copper levels above the NASEM 2021 guidelines.

Over-supplementation of trace minerals to dairy cattle can lead to excessive mineral excretion, increasing the risk of runoff of trace metal ions that contaminate water sources and harm ecosystems.

A recent study conducted in Canada⁸, evaluated the effects of feeding trace minerals above the requirements for cobalt (Co), manganese (Mn), and zinc (Zn). The control group diet was formulated to meet the NRC 2001⁹ recommendations for a 650-kg Holstein cow producing 40 kg of milk per day with a dry matter intake (DMI) of 22.5 kg/day. This diet provided the following concentrations of trace minerals: 0.24 ppm Co, 35 ppm Mn, and 89 ppm Zn. The high trace mineral diet group received increased levels of 0.78 ppm Co, 115 ppm Mn, and 168 ppm Zn. Cu and Fe levels were kept at the same level of 19 ppm Cu and 205 ppm Fe for both groups. The excretion data are summarized in Table 2.

Increasing trace mineral supplementation above dietary requirements significantly raised the output of trace minerals in both faeces and urine:

• Cobalt: faecal excretion increased by 323%, while urinary excretion rose by 505%.
• Manganese: faecal and urinary excretions increased by 298% and 272%, respectively.
• Zinc: faecal excretion rose by 175%, with urinary excretion increasing by 276%.

In a study conducted across 39 commercial farms in the US², the association between dietary mineral concentrations and trace mineral outputs in milk and manure was investigated. Elevated concentrations of trace mineral in the diet were associated with higher trace mineral excretion in manure, further underscoring the environmental implications of over-supplementation (see Table 3).

Both studies show that excessive mineral intake leads to higher trace metal ion loads in manure and urine, which in turn can lead to the contamination of soil with trace minerals. This underscores the importance of determining how many trace minerals a cow needs. It is crucial to align dietary mineral levels accordingly to support both production efficiency and environmental sustainability, and to reduce cost of a dietary diet to the minimum.

Concerns about mineral deficiencies in cattle result in over-feeding of trace minerals. Trials have shown that over-feeding of cattle with trace minerals is a common problem in many countries in the world. This can lead to trace mineral toxicity in cattle and trace mineral soil contamination.

Understanding how much trace minerals do cows need is a first step toward responsible trace mineral management. The NASEM 2021 guidelines contain mineral recommendations for cattle for the total diet. By calculating the contribution of the basal diet and comparing it to the animals’ requirements, nutritionists can accurately determine whether additional supplementation is necessary.

If the total diet fails to meet the herd's mineral requirements, supplementation should be provided at the appropriate levels to avoid copper deficiency in cows, along with deficiencies of other trace minerals. It is however more common that the ration supplies minerals above NASEM 2021 requirements. If cattle are fed trace minerals above the requirements found in the NASEM 2021 guidelines, reducing supplementary sources can offer multiple benefits. Eliminating unnecessary mineral supplements can lead to cost savings, can simplify management tasks, and can significantly reduce trace mineral excretion into the environment, which avoids trace mineral soil contamination.

How much trace minerals do cows need? The Responsible Trace Mineral programme aligns trace mineral feeding with precision nutrition strategies. Use Selko IntelliBond in a Responsible Trace Mineral programme to improve herd performance, increase farm profitability, and make dairy farming more sustainable.