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Strategies to optimize calf rumen development, nutrition and health

Anne H. Laarman and Rebecca L. Hiltz for Progressive Dairy Published on 20 July 2020

Nutrition is important at all stages of life for the dairy cow, but it is critical for young calves as they grow and mature.

How we feed and treat our calves for the first two months of life affects performance in the first two lactations: Every 1 MCal increase in intake by 8 weeks old will yield an extra 1.8 kilograms of milk and 0.09 kilogram of protein and fat in the first lactation.



Optimizing our herd’s performance begins on day one of life, not day one of lactation. Performance of our calves relies on more than just feeding the correct ration. Nutrient absorption is as important for growth and development. To facilitate a healthy transition, it is crucial to foster development of the rumen and avoid weaning calves prematurely.

Rumen development

At birth, calves have a digestive system similar to humans – no functioning rumen and no way to break down solid feed like calf starter or hay. The rumen will stay smooth and will lack the muscle and papillae needed to properly absorb nutrients. Rumen maturation begins once the calf starts to consume and ferment solid feed at 2 to 3 weeks old. Fermentation of solid feed produces butyrate, a physiological driver of papillae development, traditionally thought of as the key marker of rumen development.

Without proper development and papillae growth, the calf will not be ready to get energy from the solid feed and will suffer growth slumps at weaning.

Recently, researchers have discovered that papillae growth alone is not enough; the papillae also need to absorb nutrients. Feeding the perfect diet and maximizing papillae development is ineffective if calves cannot absorb the nutrients being given to them. In the mature rumen, volatile fatty acids (VFAs) are the primary energy source for the whole calf, so they must be effectively absorbed. There are two ways that VFAs can be absorbed:

1. Passive diffusion: Requires there to be more VFAs in the rumen space than in the rumen wall and exists at birth.


2. Guided uptake mechanisms: Facilitated and regulated by the rumen papillae, which must be developed.

Currently, we know precious little about how VFA transport systems develop. Research in 2019 at the University of Idaho and Virginia Tech showed that, at weaning, this system is still in the midst of developing and has not yet increased its VFA absorption rates. Prior to weaning, most changes in the rumen papillae are associated with growth of papillae, not VFA transport.

In a study on 7-month-old steers, VFA absorption was variable among different dietary treatments. Somewhere between weaning and 7 months old, the rumen development shifts from increasing papillae growth to increasing VFA absorption. As a result, solid feed intake and the resulting butyrate production primarily serve to increase papillae development, not VFA absorption. On-farm, this means that young calves remain reliant on milk provision for meeting energy needs, so it is crucial to avoid weaning calves prematurely.

Using nutrient absorption to improve calf health

What can we do to improve our calves’ health during these early stages? Improving gut health during this time involves feeding functional additives, such as butyrate and glutamine. In mammals, the preferred energy source of most cells is glucose, sourced from the digestion and absorption of carbohydrates. In the gut, however, butyrate and glutamine are the preferred energy sources. Butyrate powers the rumen and large intestine, while glutamine is the preferred energy substrate of the small intestine.

Supplementing calf diets with preferred energy substrates has yielded considerable health and growth benefits. Researchers in Canada, Poland and the U.S. have found butyrate fed to calves in the first week of life and during the weaning transition improves calf starter intake, growth and papillae development.

Likewise, researchers in the Netherlands and the U.S. found that supplemental glutamine in milk replacer improved small intestine development in calves fed large amounts of milk replacer. In all, supplementation offers considerable potential for improving our calves’ health and performance, provided these supplements can be supplied to, and absorbed by, the gut. In doing so, we can greatly help our calves to prepare for weaning.


Factors to consider in weaning strategies

There are a few ways to ensure the rumen is prepared for weaning. One is to wean calves at 8 weeks or later. If calves are weaned too early, regardless of their ability to consume solid feed, the rumen will not be ready to take on the full role of fermentation and absorption of energy. One study in 2015 saw that calves weaned at 6 weeks old had a much bigger drop in digestible energy intake than calves weaned at 8 weeks and took 14 days to recover to pre-weaning levels, whereas calves weaned at 8 weeks old only took four days to recover.

This is likely due to the 6-week-old rumen being less developed than the 8-week-old rumen and therefore not being physiologically prepared to absorb the nutrients being fermented. If calves are experiencing a growth slump, it is likely they are being weaned too early or too fast; adjust your weaning program accordingly.

Another popular way to ensure the rumen is properly developed is to wean by grain consumption rather than by age. It gives the slow starters a chance to catch up and achieve adequate rumen development before they are weaned. In the 2001 NRC, the benchmark is for calves to eat 680 grams of calf starter per day for at least three days in a row; this benchmark was updated in 2012 to 1 kilogram of calf starter per day.

Strategies for success

How do we use this knowledge to our advantage in calf feeding systems?

1. Ensure a steady supply of milk early on: In the first two months of life, the rumen is unable to transport VFAs at a sufficient rate to sustain growth. A larger amount of milk will help maintain growth and help fend off disease, even after weaning. If calves experience a growth slump at weaning, they are unable to maintain intake or convert intake to growth.

2.  Dietary supplementation: Using preferred energy substrates such as butyrate or glutamine can help improve feed intake, health and resilience to disease. Use according to manufacturer recommendations and monitor its success on your farm. Dietary supplementation should never be used as a substitute for good management and high-quality feeds.

3.  One change at a time: Weaning is stressful; stress compromises growth and gut health. Ensure that calves are not being weaned at the same time as they are moved into new housing or transported off-farm.

Proper rumen development before weaning is essential, driven by both solid feed intake and development of nutrient absorption capacity. By updating recent research findings into well-established practices, we continue to fine-tune our calf programs. This blend of science and practicality allows us to grow as an industry and produce healthier, more productive calves.  end mark

PHOTO: A smooth transition from a non-functioning to a functioning ruminant is critical for proper calf health, development and future performance. Farms should provide calves with good nutrition, consider feeding supplements and minimize the number of changes at once. Photo by Mike Dixon.

Rebecca Hiltz is a PhD student and graduate research assistant at the University of Alberta.

Anne Laarman
  • Anne Laarman

  • Assistant Professor of Dairy Nutrition and Physiology
  • University of Alberta
  • Email Anne Laarman