Dairy cows require at least 15 different minerals and vitamins to avoid mineral deficiencies in cattle and to maintain good health and productivity (see Figure 1). The mineral and vitamin requirements of dairy cattle depend on various factors, including genetic potential, production levels, milk yield, pregnancy status, lactation stage, and the composition of the diet.

Deficiencies of trace minerals for cattle can have a serious impact lactational performance, health, and reproduction of dairy cows. Over-supplying dairy cows with trace minerals on the other hand, can lead to:

• Increased feed costs
• Trace mineral toxicity in cattle
• Increased reactivity towards vitamins in premixes, supplements and in a TMR
• Antagonist effects with other minerals
• Decreased dairy performance
• Trace mineral ions being excreted into the environment, leading to trace mineral soil contamination

The goal of responsible trace mineral management is optimal mineral supply, avoiding trace mineral deficiencies in cattle, but also avoiding trace mineral toxicity in cattle through excessive mineral supplementation and avoiding higher costs without a return on investment.

Over-supplementation of trace minerals is a common issue in dairy herds
Studies on commercial dairy farms in Canada¹ and the US² showed that mineral supplementation in commercial dairies frequently exceeds the NASEM guidelines³ (see Table 1).

Table 1: Trace mineral levels fed in 139 dairies compared to NASEM 2021 guidelines for dairy cattle.
Over-supplementation of copper results in accumulation in the liver of dairy cattle
Studies carried out in the UK⁴, US⁵ and the Netherlands⁶ show that feeding copper above the NASEM guidelines for dairy cattle resulted in elevated liver copper concentrations, leading to a significant risk of chronic copper toxicity in dairy cattle. These studies confirm that over-feeding trace minerals is a global issue, with significant risks of trace mineral toxicity in cattle and trace mineral copper soil contamination.

Over-supplementation of copper has a negative effect on performance and fertility
A longitudinal study conducted in the UK⁷ showed that feeding heifers a diet with copper levels above the NASEM 2021 guidelines resulted in poor fertility (see Figure 2).

Over-supplementation of trace minerals increases the risk of environmental contamination
A recent study conducted in Canada⁸ showed that feeding cobalt, manganese and zinc above the NASEM 2021 requirements for dairy cattle significantly raised the output of trace minerals in both faeces and urine.

Dairy herds should receive the correct amount of trace minerals to prevent deficiencies without causing over-supplementation. A process in 3 steps can assure that dairy cows will be fed according to the NASEM guidelines.

Step 1: Understand the NASEM 2021 guidelines for dairy cattle
The NASEM guidelines for dairy cattle serve as benchmark for formulating diets that meet the specific needs of lactating and non-lactating dairy cows. The NASEM guidelines are based on total diet.

Step 2: determine how much trace mineral is already present in the basal ration of dairy cattle
The basal ration of dairy cows is defined as the combination of all forages and by-products, without compound feed and supplements. Neglecting the trace minerals naturally present in forages and by-products can result in over-supplementation.

Values from a model^13,35 based on 5,000 dairy diets were used for modelling the risk for inadequate trace mineral intake. The Trouw Nutrition R&D team calculated the distribution of copper (Cu), zinc (Zn) and manganese (Mn) levels in those 5,000 diets (see Table 2).

Table 2. Trace mineral levels (ppm) for Cu, Zn and Mn in different dairy diets: distribution across percentiles.
The 1% percentile from Table 2 is being used to calculate the minimum level of trace mineral that needs to be supplemented to minimise the risk of underfeeding.

The 99% percentile from Table 2 is being used to compare the maximum level of trace mineral that is supplemented to the tolerance level according to the NASEM guidelines, thus reducing the risk of overfeeding.

The NASEM recommendation for Cu level for the total diet is 10 ppm. The 1% percentile for Cu in Table 2 is 5 ppm. This means that if the value of 5 ppm is being used for the calculation, there is a 99% chance that the actual diet fed on the farm has a higher level of Cu, reducing the risk of under-feeding to 1% or less. Thus, the recommended supplementation level is 10ppm – 5ppm = 5 ppm of Cu.

The upper tolerance level for Cu in the NASEM 2021 guidelines is 25 ppm. The 99% percentile for Cu in the basal diet is 18 ppm. This means there is a safety margin of 25 ppm – 18 ppm = 7 ppm. Thus, supplementation of Cu should not exceed 7 ppm.

Thus, supplementing 5-7 ppm Cu is sufficient to meet the cow's needs while avoiding over-feeding. Similar calculations were made for zinc and manganese (see Table 3).

The final step is to calculate the total amount of Selko IntelliBond hydroxy trace minerals that needs to be included in a diet of a cow consuming 22.5 kg of DM to meet the total recommended levels from the NASEM 2021 guidelines. Table 4 shows the calculation of the shortfall, and the Selko IntelliBond inclusion rates required for supplementation in addition to the basal diet.

After supplementation with Selko IntelliBond hydroxy trace minerals for cattle, the final diet precisely meets the NASEM 2021 recommendations for trace minerals for cattle, ensuring both nutritional adequacy and environmental stewardship.

The NASEM guidelines are based on inorganic trace mineral sources. Comparative studies^11,12,17,20 in cattle have consistently shown the superior bioavailability of Selko IntelliBond hydroxy trace mineral sources over sulphate-based minerals sources (see Figure 3). Mineral absorption in dairy cattle is a regulated process, bioavailability varies not only between mineral sources, but also according to the dietary concentration of trace mineral provided. If trace minerals are fed below requirements, absorption is high, if fed well above requirements, absorption is low. This means that if supplementation levels are being reduced, absorption is likely to be upregulated, reducing the risk of under-feeding.

Reducing the level of supplemented trace minerals fed will reduce the amount of free metal ions in the rumen, which has a positive impact on rumen function, leading to several significant positive effects in dairy cows. Selko IntelliBond hydroxy trace minerals are largely insoluble at rumen pH, they release their trace mineral ions gradually in the duodenum once the pH drops to 4.0. Switching to Selko IntelliBond hydroxy trace minerals leads to a further improvement of rumen function in dairy cattle, which enhances the effects of a responsible mineral approach further.

Enhanced lactational performance of dairy cows
Reducing the amount of trace minerals in a dairy ration reduces the amount of free metal ions in the rumen, which leads to an improvement of rumen function of dairy cows. Switching to Selko IntelliBond hydroxy trace mineral supplements for dairy cattle results in an additional improvement of rumen function. Studies have shown that feeding Selko IntelliBond to dairy cattle improves NDF and DM digestibility^{14,15,16,17,18,19,20,21,22}, improves rumen function^31,32,33,34, and supports cow health²³. These improvements contribute to better colostrum quality²⁶, boost fertility^24,25 and improve lactational performance^22,26,27, with an increase in energy-corrected milk (ECM) yield of 1.4 kg/cow/day (see Figure 4).

Reduced risk of contamination of the environment with metal ions
Reducing the amount of trace minerals in a dairy ration reduces the risk of excretion of trace minerals into the environment. Trials¹⁰ have shown that the use of Selko IntelliBond hydroxy trace minerals reduces excretion of trace metal ions into the environment even further.

Reduced carbon footprint per kg of ECM produced
Selko IntelliBond for dairy cattle was the first improved source of trace mineral nutrition with a Life Cycle Assessment (LCA) that demonstrated a reduction in carbon intensity of milk production, decreasing CO₂ equivalents per kilogram of ECM by 1.5–2.0 %^28,29.

The increase in ECM production translates into a strong economic benefit. Depending on milk prices and feed costs, the ROI for feeding Selko IntelliBond can range from 12:1 to 15:1, based on the improvement of lactational performance only. If other benefits (improvement of health and fertility, reduced culling rate and reduction of CO₂ equivalents per kilogram of ECM) are considered, this ROI is even higher.