Weaning calves: an age question or an intake question?

The weaning age and process for calves continues to be debated in the dairy industry. While there remains little agreement on a single best practice for weaning, research generally agrees that gradual and later weaning is better.

Jim Quigley of Calf Notes recently highlighted the work of Aarhus University in Denmark. The Aarhus group performed a comprehensive literature review and described a consensus for positive effects on the overall growth of calves weaned at later ages by using a longer weaning duration.

Specifically, the group determined there were “positive effects on the overall growth of calves weaned at later ages, over longer durations, based on starter intake, or weaned using step-down approaches.” However, they found few studies with an adequate scale to measure health results of different practices, nor could they provide a specific benchmark for weaning age.

Quigley suggests that our continued focus on selecting a specific age as a weaning metric for the industry is perhaps incorrect. Rather, he suggests we should approach weaning from a nutritional approach, which might be different for each farm.

According to Quigley, weaning in ruminants should occur when the digestive system is sufficiently developed to provide sufficient nutrients from solid foods in place of the liquid diet. Additionally, peripheral organ systems such as the liver, adipose tissue and muscle must adapt from nutrients provided by monogastric-type digestion to those of rumen fermentation. These processes are not driven by age but rather by consumption of solid feeds, i.e., calf starter, and production of volatile fatty acids in the rumen.

So, if we want to utilize the nutritional approach, the real focus needs to be on how much starter is consumed, as this will drive the development of the rumen and allow the calf to digest non-fiber carbohydrates such as starch. This specific ability to digest NFCs is critical to successful weaning. When the rumen is not sufficiently developed for starch and other nutrients in calf starter, a post-weaning slump is often observed, where the calf struggles to grow, experiences stress and often has loose feces, sometimes to the point of diarrhea.

A 2019 paper by Quigley identified that sufficient rumen development occurred when calves had consumed a total of 15 kg (33 pounds) of NFC from calf starter. Note this is not kilograms or pounds of starter. However, I find that we don’t normally measure calf starter intake or NFC intake. So how do we determine when to wean calves?

Quigley suggests that a farm could estimate the intake of starter and NFC using growth and intake models to determine a farm’s weaning age. The National Academies of Science, Engineering and Medicine, Cornell and the University of Vermont all have models available to generate a predicted age where rumen development is sufficient.

CalfSim, the model by Costa’s lab at the University of Vermont, is free and allows the user to input the liquid feeding program and starter details. The program then predicts nutrient intake from liquids and dry feeds and calculates the total NFC intake. It then reports the age at which calves are ready to be weaned. Keep in mind that utilizing a gradual weaning process is beneficial, especially as we choose to feed more milk in the first 60 days of life.

In summary, weaning dairy calves should be based on physiological readiness, or rumen readiness, rather than a fixed age, as rumen development is the key driver of successful transition from milk to solid feed. Quigley’s research has shown that rumen maturity depends primarily on the intake of calf starters, especially non-fiber carbohydrates such as starches and sugars, rather than chronological age. When calves consume approximately 15 kg of NFC from starter feed, their ability to extract energy closely matches that of a mature ruminant, marking an important benchmark for weaning readiness and minimizing post-weaning growth slumps.

I would encourage you to work with your nutritionist or calf advisor and use available tools, such as the University of Vermont’s CalfSim, to model liquid feeding programs and estimate when calves reach an age where rumen development is adequate. Focusing on readiness allows producers to implement appropriate step-down weaning strategies that reduce stress and support a smooth transition to dry feed, shifting attention away from an industry weaning age toward weaning at the right time for optimal calf development and performance.

Megan Weisenbeck practices primarily dairy production medicine in Minnesota and Wisconsin. Megan can be reached at meganweisenbeck.dvm@gmail.com.