Introduction
Interest in weaning strategies for young dairy calves continues to grow,
especially as more farms feed larger amounts of milk or calf milk replacer (CMR).
These programs can improve nutrient supply and early growth, but they may
also delay calf starter intake. When liquid feed is reduced or removed, the calf
must be able to obtain sufficient nutrients from dry feed to maintain growth. So,
how can we estimate when a calf is ready?
In research published in 2019, my colleagues and I found that cumulative intake
of nonfiber carbohydrate (NFC) from calf starter was closely related to the
development of the calf’s ability to extract energy from starter (Quigley et al.,
2019a,b). We proposed 15 kg of cumulative NFC intake (cNFCi) as a useful
indicator of gastrointestinal maturity, and I discussed the concept in Calf Note
#209. Since then, the 15-kg target has attracted increasing interest—and
appropriate scrutiny. It is a practical benchmark, not a biological switch or a
guarantee of trouble-free weaning. Adequate starter intake, nutrient supply, calf
health and the weaning transition itself remain important.
Calculating the age at which calves reach 15 kg cNFCi is not always easy. The
amount of starter consumed changes daily, milk allowance affects dry feed
intake, and the NFC concentration of the starter must be known or estimated.
Fortunately, three freely available resources can help.
Three tools to help
- Calf Note #230 – a simple Excel spreadsheet. In Calf Note #230, I provided an
updated spreadsheet based on our dry feed intake prediction equations (Quigley
et al., 2021). Enter the milk feeding program and starter NFC concentration to
estimate the age at which the calf reaches 15 kg cNFCi. This is the easiest option
for a quick estimate, although it provides less information than either simulation
model. Read the Note and download the spreadsheet here: Calf Note #230 - CalfSim – an online simulation. Developed by Dr. João Costa and colleagues,
CalfSim is an easy-to-use, browser-based program for evaluating liquid feeding
strategies, predicted starter intake, growth and feeding costs (da Silva and Costa,
Calf Notes.com
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2025). There is nothing to install. Dr. Costa has left the University of Vermont, and
some older university links to CalfSim no longer work. The updated official
address is www.calfsim.com. If that address does not redirect correctly—or your
browser has cached an older address—use this direct application link:
https://teds-91-calfsim.share.connect.posit.cloud/. I recommend keeping the direct
link handy.
3. NASCalf – a detailed desktop simulation. NASCalf is a downloadable
Windows program available from Calf Notes Tools. It estimates daily feed intake,
cumulative NFC intake, nutrient supply, requirements and growth using a
simulation based on the 2021 NASEM model, with additional analysis and
reporting options. It provides the most detailed information of the three tools, but
also requires more time and training to use effectively. Access NASCalf and the
supporting documentation at Calf Notes Tools or go directly to the NASCalf page.
Which should you use?
For a quick estimate of the 15-kg cNFCi milestone, start with the spreadsheet in
Calf Note #230. If you want to compare milk feeding programs without installing
software, try CalfSim. If you want to examine day-by-day nutrient supply and
growth in greater detail, NASCalf is the better choice. Remember that predicted
intake is not a substitute for observing actual calf starter consumption and calf
performance.
Both CalfSim and NASCalf are being developed further. Watch for new
capabilities and options as these tools evolve. I hope these resources make it
easier to evaluate weaning strategies and design programs that support a smooth
transition from milk to dry feed.
Best of luck!
References
Da Silva, T. E. and J.H.C. Costa. 2025. CalfSim tool: A free and user-friendly decision
support tool for designing and simulating optimized feeding plans for dairy calves—A
prediction assessment study. JDS Communications. 6:654-659.
Quigley, J. D., W. Hu, J. R. Knapp, T. S. Dennis, F. X. Suarez-Mena, and T. M. Hill. 2019a.
Estimates of calf starter energy affected by consumption of nutrients. 1. Evaluation of
models to predict changing digestion on energy content in calf starters. J. Dairy Sci.
102:2232–2241. https://doi.org/10.3168/jds.2018-15353
Quigley, J. D., W. Hu, J. R. Knapp, T. S. Dennis, F. X. Suarez-Mena, and T. M. Hill. 2019b.
Estimates of calf starter energy affected by consumption of nutrients. 2. Effect of
changing digestion on energy content in calf starters. J. Dairy Sci. 102:2242–2253.
https://doi.org/10.3168/jds.2018-15354
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Quigley, J. D., T. S. Dennis, F. X. Suarez-Mena, C. E. Chapman, T. M. Hill, and K. M. Aragon.
2021. Models to predict dry feed intake in Holstein calves to 4 months of age. J. Dairy
Sci. https://doi.org/10.3168/jds.2020-19581
da Silva, T. E., and J. H. C. Costa. 2025. CalfSim tool: A free and user-friendly decision
support tool for designing and simulating optimized feeding plans for dairy calves—A
prediction assessment study. JDS Commun. 6:654–659.
https://doi.org/10.3168/jdsc.2025-0777