Written by Dr. Grace Cun and Dr. Andy Mueller
A calf’s future productivity begins long before entering the milking herd, or the beef supply chain. One of the most important milestones during the preweaning period is developing a functional rumen for a successful transition from milk to solid feed. Recognizing the importance of early rumen development, the latest Dairy Calf and Heifer Association (DCHA) Gold Standards recommend calves consume at least 33 pounds of cumulative non-fiber carbohydrates (NFC) before weaning. Because NFC includes starch, sugars, and soluble fiber, the recommendation recognizes that successful rumen development depends on the total intake of fermentable carbohydrates, rather than one carbohydrate source.
For years, calf nutrition has centered on starch-rich starters because they consistently promote rumen development. While that approach remains valid, we’ve learned that the developing rumen isn’t responding to starch itself but responding to the products of microbial fermentation. As calves consume starter and water, rumen microbes ferment carbohydrates into VFAs, particularly butyrate, which stimulates rumen papillae development and increases the rumen’s absorptive capacity. This allows calves to better utilize nutrients from solid feed and transition more smoothly through weaning.
Fermentation, however, cannot occur without water. Fresh water is often overlooked during the preweaning period, yet it is essential for establishing rumen microbes and supporting fermentation. While milk bypasses the rumen through the esophageal groove, water enters the rumen, creating an environment needed for microbial colonization and VFA production.
Rather than maximizing starch, calf starters should provide a balanced supply of fermentable carbohydrates that fuel rumen microbes, optimize fermentation, and promote rumen development.
Not All Carbohydrates Are Created Equal
Although starch, sugars, and soluble fiber all support rumen fermentation, they ferment at different rates and produce different VFA profiles. Together, they provide rumen microbes with a more consistent supply of fermentable substrate, creating a more balanced fermentation pattern.
Starch
Starch remains the foundation of most calf starters because it is readily fermented and efficiently supports VFA production. However, many commercial starters contain 30–40% starch, and diets that rely too heavily on starch can increase the risk of rapid fermentation, lower rumen pH, and ruminal acidosis, potentially impairing rumen development and nutrient absorption.
Recent research also suggests that starch is not the only fermentable carbohydrate needed to support optimal rumen development and calf performance. In a Cornell study, calves were fed a starter containing approximately 20% starch, 15% sugars, and soluble fiber. Calves experienced minimal post-weaning growth depression, and the authors suggested that this carbohydrate profile may have promoted greater butyrate production and rumen development (Molano et al., 2020). Similarly, Iowa State researchers found that beef × dairy calves fed a lower-starch starter (15.6% vs. 26.3% starch) achieved similar weaning weight, average daily gain, and frame growth as calves fed the higher-starch starter (Klipp et al., 2024). Together, these findings suggest that balancing fermentable carbohydrate sources, rather than simply increasing starch concentration, can support rumen development, calf growth, and a successful transition through weaning.
Sugars
Sugars, such as sucrose, provide another rapidly fermentable energy source for rumen microbes. Research has shown that sucrose fermentation can produce more butyrate than starch, highlighting that sugars can be an effective tool for supporting rumen development. Sugars complement the ration by providing an additional source of fermentable carbohydrate that fuels microbial activity and VFA production. Ingredients high in sucrose, such as molasses, may also improve starter palatability, encouraging earlier and more consistent starter intake.
Soluble Fiber
Soluble fiber supports rumen development by providing another substrate for microbial fermentation. Although it produces more acetate than butyrate, it complements starch and sugars by broadening the supply of fermentable carbohydrates available to rumen microbes, supporting microbial diversity and a more balanced fermentation profile.
What This Means on the Farm
Successful rumen development isn’t about maximizing one carbohydrate source; it’s about optimizing fermentation. That starts with offering clean water early in life, encouraging consistent starter intake, and formulating calf starters with a balance of starch, sugars, and soluble fiber. As our understanding of rumen biology continues to evolve, the future of calf nutrition may be defined less by a single carbohydrate source and more by how well we support microbial fermentation that drives rumen development.
References
- DCHA Gold Standards. 2026. https://calfandheifer.org/
- Molano R, Saito A, Luchini D, VanAmburgh M. Effects of rumen-protected methionine or methionine analogs in starter on plasma metabolites, growth, and efficiency of Holstein calves from 14 to 91 d of age. Journal of Dairy Science, 2020; 103, 10136-10151. https://www.journalofdairyscience.org/article/S0022-0302(20)30721-9/fulltext
- Klipp T, Jayasooriya, R, Tyler H, Carpenter A. 2024. Evaluating the management and growth of pre-weaned beef × dairy calves. Master’s Thesis. Iowa State University. https://dr.lib.iastate.edu/server/api/core/bitstreams/156c4ba0-3e14-4fd7-8ca0-8c16c4e77da2/content
