Smart Calf Rearing Conf. - How Trouw Nutrition’s Juliette Wilms is redefining fat in milk replacer formulation

1 December 2025

6 minute read

By: Sarah Mikesell

Europe

North America

Editor's note: From September 25 to 27, the international Smart Calf Rearing Conference took place at the University of Madison in Madison, Wisconsin. Organized by Förster-Technik, Trouw Nutrition, the University of Guelph and the University of Wisconsin – Madison, the conference brought together 245 participants from around the globe to discuss the latest findings in calf physiology, health, housing and welfare, and 18 renowned speakers shared their expertise and research insights. Participants also had the opportunity to visit the university’s calf barn, where innovative solutions for calf rearing were showcased – including the CalfRail feeding system for individual housing, developed by Förster-Technik.

When calves are born, they start life with low fat reserves – only about 3% body fat compared with roughly 15% in human infants – and will deposit fat after birth to create fat stores as energy reserves. For Juliette Wilms, researcher at Trouw Nutrition and presenter at the Smart Calf Rearing Conference, this difference is not trivial. It’s central to understanding that all mammalian neonates are depositing fat after birth and to do that they need a high fat liquid feed fed at high plane of nutrition. 

“Calves are the only farm animals that are severely restricted, especially in the neonate phase, in terms of nutrient supply,” Wilms explained. “In pediatrician research, we can’t compare the long-term effect of calorie-like nutrition because babies get as much milk as they want. Calves don’t.”

That contrast, she argued, has profound consequences not just for daily weight gain but for lifelong resilience, regulation of metabolic programming, immune competence and metabolic programming.

Evolutionary design of milk

According to Wilms, milk is not merely a source of nutrition but it’s an evolutionary communication system between dam and offspring. 

“The composition of milk is not random,” she said. “It ensures the survival of the neonate and the formation of the species.” 

Over millions of years, milk has evolved to cover the energy needs and physiological needs of the developing calf, adapting to the needs of the calf through subtle biochemical signaling. That balance can be disrupted in modern rearing systems.

Milk replacers are convenient and consistent but fundamentally different in composition from natural bovine milk. They contain roughly half the fat of cow’s milk – about 18% versus 30% – and rely on alternative fat sources from vegetable or animal origin as their primary lipid source. 

“We are feeding a liquid diet that presents large macronutrient imbalances compared to bovine whole milk,” Wilms said.”

The result is a diet that may sustain growth effectively but may challenge long-term metabolic regulation. According to Wilms, the imbalance between fat and carbohydrates changes how energy is metabolized, influencing everything from insulin sensitivity to organ development to immune response.

The concept of “metabolic programming”

Metabolic programming is the idea that nutrition during early life can permanently alter physiology and gene expression. 

“Exposure during critical windows of development, such as the fetal or pre-weaning phase, can cause lasting changes in metabolism and resilience,” she explained.

Evidence from human infant studies supports the theory. Decades ago, infant formulas were reformulated to match the amino acid requirements of human infants using dairy proteins. 

“That was seen in a high concentration of insulin-releasing amino acids in the bloodstream, stimulating IGF-1 and insulin secretions and leading to higher weight gain in infancy,” Wilms noted. “During childhood and adulthood, this was linked with a higher risk of obesity and cardiovascular disorders.”

She drew an important parallel to calf feeding practices today.

“We must consider how we are programming our calves,” she said. “We are feeding them milk replacers that present those imbalances in lactose and sometimes protein.”

An overreliance on lactose as the main energy source in liquid diets may set calves on a metabolic trajectory that favors rapid early growth at the expense of long-term energy regulation.

The case for more fat – and the right kind

To test whether higher fat inclusion could improve calf outcomes, Wilms and her colleagues at Trouw Nutrition conducted controlled feeding trials comparing milk replacers with varying macronutrient compositions. 

In one study, calves were fed a “high-fat” replacer containing 25% fat – still below the 30% in whole milk – versus standard formulations with higher lactose and protein.

Although average growth rates were similar, calves fed milk replacer high in fat displayed a more favorable metabolic profile in line with that of calves fed bovine whole milk. 

When looking at calves fed high plane of nutrition (8.0 L/d vs. 4.0 L/d) and therefore having a higher fat intake, those calves had a higher fat accumulation in the organs, and the gene expression pointed in that direction.

“In adipose tissue, we saw an increase in oxidative metabolism, higher adipocyte differentiation, higher brown-like adipocytes and lower inflammation. These are positive indicators of healthy growth and metabolic development,” she said. 

In practical terms, calves build fat reserves they can later mobilize during times of stress, like illness or weaning. 

She noted a large US study of 2,300 pre-weaning dairy heifers that identified fat intake from the liquid diet as one of the top three predictors of survival, along with birthweight and serum IgG status. 

“They found that the higher the fat intake from the liquid diet, the lower the mortality,” Wilms said. 

For years, the dairy industry has viewed visible fat accumulation in young calves as undesirable. Wilms challenged that assumption noting that while excessive body fat in post-weaning heifers can impair milk yield later, there is no evidence that higher body fat during the pre-weaning period has the same effect. 

“Dietary fat is actually the most efficient energy source,” she said.

Fat composition matters

Increasing the percentage of fat is only part of the solution. The type of fat also matters. Most commercial milk replacers use blends of palm and coconut oil, but these differ markedly from bovine milk fat in both fatty acid profile and triglyceride structure. 

“All high-fat milk replacers are not equal,” Wilms stressed. “Fat quality and the way in which it’s incorporated in the powder are very important.”

In a series of trials, Wilms tested milk replacers containing different fat blends and found that dairy cream was the superior fat source, but it’s not a commercial option due to cost.  

Bovine milk fat naturally contains a unique spectrum of short- and medium-chain fatty acids – particularly butyric (C4) and caproic (C6). These molecules are biologically active: they modulate intestinal and rumen development, enhance gut integrity (lower diarrhea incidence) and increases insulin sensitivity.

To restore these missing elements, her team experimented with adding tributyrin, esters of butyric and caproic acid, to the fat fraction of milk replacers. 

The study showed that calves fed the milk replacer with tributyrin had higher voluntary milk and postweaning starter feed intake. When calves were necropsied at five weeks, researchers observed clear signs of accelerated rumen development in the tributyrin group, including well-developed papillae. 

“We think tributyrin sends a signal to the gut to develop the rumen. When we initiate the rumen, the calves have a higher surface area for VFA absorption and can eat a little more starter feed earlier,” she said. 

Calves fed the tributyrin formulation also required fewer veterinary treatments overall, particularly for respiratory conditions. 

For Wilms, these findings challenge entrenched assumptions about what defines an “ideal” calf. 

“We need to rethink what defines the ideal dairy-calf phenotype,” she said. “Should we focus only on growth, or also on resilience and long-term metabolic health?”

Her data suggest that re-aligning milk replacer composition with the biological blueprint of cow’s milk could pay dividends across all three. Higher fat intake not only improves short-term performance and survival but may also lay the groundwork for more robust, efficient cows later in life.