Changes to the daily nutrient requirements and the adequate nutrient intake
In the old 2001 NRC Guidelines, many of the key nutrients in dairy cattle were reported without explaining exactly what daily requirements mean. In the current version, two important terminologies are used for trace minerals: firstly, daily nutrient requirement (Req.) is defined as the average nutrient intake estimated to meet the requirements of half of the healthy individual animals in specific gender group and life stage. Secondly, adequate nutrient intake (AI) is defined as the average daily nutrient intake that a group of experts have defined based on limited experiment data. Daily nutrient requirements and adequate nutrient intake are presented in Tables 1 and 2.
Changes to the mineral absorption coefficients
Next to the nutrient requirements and the adequate intakes, the absorption coefficients were also re-evaluated. Changes to trace mineral absorption coefficients in the new NASEM 2021 guidelines compared to the old NRC 2001 guidelines are presented in Table 3.
Comparing models to establish trace mineral and vitamin levels
Nutrient requirements of dairy cows differ according to body weight, average weight gain, milk production, dry matter intake, lactation phase and gestation. Predicted trace minerals and vitamins concentrations that are required on a dry matter basis to meet these requirements therefore also differ. New insights have resulted in changes between the old NRC 2001 and new NASEM 2021 guidelines. The new values are presented in Table 4.
Compared to the old NRC 2001 Guidelines, major changes apply for Mn and Zn, with increases in concentration ranging from 20% to 100% in dry and lactating dairy cows. Major changes also occurred in the required concentrations for Cu which reduced by 10 to 20% in lactating dairy cows and increased by 15% in dry cows. Additionally, Co concentration was set 0.2 mg/kg of DM in the NASEM 2021 guideline, almost double the concentration compared to the previous NRC 2001 guideline.
For vitamins, significant increases of 10 to 20% in were seen in vitamins A and D levels in lactating dairy cows. For vitamin E levels, especially for far-off and close-up dry cows respectively, much larger increases of 100% and 200% were seen.