The transition cow is often discussed as having an energy problem. Cows eat less, demand ramps up and they fall into negative energy balance. While true, this is only part of the story. The bigger issue is a logistical bottleneck: What happens to the fat that gets mobilized? If the cow cannot move that fat out of the liver efficiently, metabolic problems stack up quickly.
Why the Liver Gets Overwhelmed
Around calving, a cow’s dry matter intake drops by 30% to 35%, while energy demand increases sharply. To fill this gap, the cow mobilizes body fat and sends it to the liver. Once there, the fat follows three main paths:
- Complete Oxidation: It is burned for fuel to generate ATP (energy).
- Ketogenesis: It is converted into ketones.
- Export: It is packaged and sent back into circulation to be used for milk synthesis.
When the volume of fat exceeds the liver’s capacity to process it, the system breaks down.
“Lipolysis happens, that adipose tissue is breaking down. Part is going to be used for milk synthesis, part is going to go for complete oxidation and generate ATP and part goes to ketogenesis. The third thing that happens is that triglycerides accumulate, and when the liver cannot keep up, fat builds up in the liver and we start to see metabolic problems in cows,” says Fabio Lima, assistant professor at UC Davis School of Veterinary Medicine.
Choline as the Liver’s “Shipping Crate”
The fundamental struggle for the modern dairy cow is her low capacity to export triglycerides from the liver as very low-density lipoprotein (VLDL). Choline is the key ingredient needed to build the VLDL “package” that carries fat out of the liver cells.
“What we know about our modern dairy cows is that they have a low capacity to export triglycerides from the liver as VLDL. That inability to increase fatty acid oxidation or export is what leads our cows to develop fatty liver. Choline has been shown to be a key ingredient to reverse that,” Lima says.
By supporting the synthesis of phosphatidylcholine, a specific fat-transporting molecule, choline ensures the liver can keep up with the surge of fat mobilization.
“The modern dairy cow has been selected for high production. That creates a demand that makes nutrients like choline strategically important. It helps support that level of production,” Lima explains. “Choline is critical for VLDL assembly and hepatic fat export. And it’s critical to reduce fatty liver risk and minimize its impact. Phosphatidylcholine seems to depend on adequate choline, especially during the transition period.”
Why Rumen-Protection is Non-Negotiable
While choline is present in common feed ingredients like soybean meal, canola meal and forages, it is almost entirely degraded by rumen microbes before the cow can use it. Because natural feed sources rarely provide enough absorbable choline to meet the high demands of early lactation, rumen-protected choline is added to ensure the nutrient reaches the small intestine for absorption.
Despite the clear biological mechanism, the dairy industry is still refining exactly how much choline a cow needs. Because rumen dynamics are complex and every cow mobilizes fat differently, providing a one-size-fits-all dose remains a challenge.
“There has been 40 years of research, and we think, ‘Well, 40 years is a lot of research, we’re probably going to get some clear guidance.’ But we’re still not sure. There’s still the rumen dynamics and how much is metabolized, where it goes. All those things that make it difficult,” Lima says.
Rethink Transition Management
Success in the transition period requires looking beyond the feed bunk. The critical question is no longer just “Is she eating enough?” but rather: Is the transition cow able to handle the fat she is mobilizing?
Instead of focusing only on energy intake, it is equally important to consider how effectively the cow can process and move that energy. Supporting liver health through fat export is one of the most direct ways to reduce metabolic disorders and improve performance in the modern dairy cow.
