NASCalf Demo – NASCalf and NASEM Comparison
Hello, and welcome to this demonstration of the NASCalf growth simulation model.
In this demo, we’re going to compare growth predictions from NASCalf with those generated by the NASEM 2021 model, using the NASIM software available from the official NASEM website.
To make a fair comparison, we need to enter the same basic animal, diet, and intake information into both models. It’s important to remember that NASCalf simulates growth continuously from birth through four months of age, while the NASEM model predicts growth for a single day at a time. Because of that difference, we’ll use NASCalf to generate predicted intake and body weight on a specific day, and then enter those values into the NASEM model for comparison.
Let’s begin by defining the feeding program used in both models. In NASCalf, calves receive colostrum on day one, transition milk on days two and three, and then milk replacer beginning on day four. Milk replacer is fed until weaning on day 70. From day four through day 14, calves receive a 26:17 milk replacer. We’ll evaluate growth on two specific days later in the simulation.
For this comparison, it’s critical that feed nutrient composition is identical in both models. To keep things simple, we’ll use only two feeds: a 26:17 milk replacer and a 22% protein, high-starch calf starter. Nutrient composition for both feeds comes directly from the NASEM feed library and is entered into NASCalf using the same values.
For all feeds, we’ll match dry matter, protein, fat, and ash. For the calf starter, we’ll also match ADF, NDF, starch, and lignin. In this example, we’re not offering any forage, so only milk replacer and starter are included.
Once feed composition is aligned, each model will independently calculate metabolizable energy and metabolizable protein using its own equations. The next step is to ensure that, on the specific comparison day, both models are using the same animal characteristics and feed intakes.
The calf is a Holstein with a birth body weight of 42 kilograms and a mature body weight of 680 kilograms. We’ll set the target average daily gain prior to weaning at 700 grams per day. For simplicity, ambient temperature is fixed at 20 degrees Celsius.
The milk feeding program is as follows:
From days 4 to 14, calves receive 680 grams of milk replacer powder per day.
From day 15 through day 49, intake increases to 900 grams per day.
Milk feeding ends on day 70, which is the final day before weaning.
With this feeding program in place, we can go to the Diagnostics menu and select Supply Calculations. This allows us to view NASCalf’s predicted values for any individual day. Scrolling down to day 56, we see the predicted body weight and dry feed intake for that day.
On day 56, liquid intake is 0.57 kilograms of dry matter, which is fixed by the feeding program. NASCalf predicts a calf starter intake of 1.46 kilograms of dry matter. The predicted body weight on this day is 79.55 kilograms.
We can now transfer this information directly into the NASEM model. In NASEM, we enter an age of 8 weeks (that is, 56 days of age), a body weight of 79.55 kilograms, and a mature body weight of 680 kilograms. Milk replacer intake is set to 0.57 kilograms of dry matter, and non-liquid intake is set to 1.46 kilograms.
You’ll notice that the NASEM model initially predicts a slightly lower starter intake. For this comparison, we override that value and use the NASCalf-predicted intake so both models are evaluated using identical inputs.
At this point, both models have the same body weight, milk replacer intake, and starter intake. Any remaining differences in predicted growth will therefore be due to how each model calculates metabolizable energy and metabolizable protein supply, and growth requirements.
This slide summarizes the key input values used in both models, including age, body weight, mature body weight, temperature, and feed intake. On the right, we see the nutrient composition calculated by each model. Dry matter differs because the NASEM model assumes milk replacer is fed at 12.5% solids, while NASCalf performs all calculations strictly on a dry matter basis.
Protein values are very similar. Ash is not reported by the NASEM model but is calculated by NASCalf. Starch, NDF, gross energy, and metabolizable energy are all very close, with only minor rounding differences. Metabolizable protein as a percentage of dry matter is identical. NASCalf also reports RDP and RUP values, which are not shown in the NASEM output.
Looking next at energy and protein requirements, we see that metabolizable energy required for maintenance is identical at 2.81 megacalories. Energy required for gain is very similar between models, with small differences reflecting simplifications used in NASCalf relative to the full NASEM equations.
Total ME intake and ME available for gain differ by only a few hundredths of a megacalorie. As a result, predicted allowable gain based on ME is essentially the same in both models.
Metabolizable protein calculations show even closer agreement. Maintenance, growth, and total MP requirements differ by less than two grams. MP intake differs by less than one gram, and both models predict the same MP-allowable gain.
Overall, we see that NASCalf and the NASEM model generate very similar predictions for intake, energy supply, protein supply, and growth. Minor differences in metabolizable energy calculations exist, particularly for dry feeds, but these differences have minimal impact on predicted performance. We have compared the two models under a wide variety of conditions, feeding programs, and starting body weights. We find that the models provide nearly identical predictions of nutrient supply and requirements, and, therefore, similar predictions of growth. At the end of the day, predictions using the NASCalf model are similar to those of the NASEM model on any day. The advantage of the NASCalf model is availability of more diagnostic information, the ability to change some of the assumptions used by the model, and prediction of additional nutrients such as RUP, RDP and amino acids.
That concludes this comparison of growth predictions between NASCalf and the NASEM model. Thanks for watching, and we’ll see you soon in the next demonstration.
