Publication of “Nutrient Requirements of Dairy Cattle” by the National Academy of Sciences, Engineering, and Medicine (NASEM) in 2021 was a watershed moment in dairy cattle nutrition. The text represented incorporation of more than 20 years of research into a new model of dairy cow nutrition. A team more more than 20 internationally recognized scientists at research instititues from all over North America were involved in the exhaustive review of all the research published since the last NRC publication, in 2001.
The NASEM publication contained an updated calf model in Chapter 10, and heifer model in Chapter 11. Both incorporated aspects of the larger cow model – for example, calculation of energy supply from calf starters and grower utilized the framework for calculating ME supply for adult animals. Also, a significant update was made in terms of protein nutrition. The model no longer relied on “Biological Value” as an index of protein quality, but rather on “Metabolizable Protein” (MP) – an approach long used in dairy cow nutrition.
Altogether, the NASEM Publication represented and represents an amazing improvement in our understanding of calf and heifer nutrition. However, there were still some “missing pieces”.
Like previous nutrition models, the NASEM Publication predicts nutrient requirements at one point in time – that is on one day. For calves, the model predicts metabolizable energy (ME) and MP requirements and supply, and then predicts body weight gain from these values. There is no provision for following growth over time, which is critical to understand the implications for – say, weaning strategy or volume of milk to feed and it’s effect on later starter intake. Therefore, there was a need to not only predict growth on one day, but throughout the entire calf (and heifer) period. A growth simulation, based on daily NASEM predictions, was needed.