Managing Energy Partitioning in Lactating Dairy Cattle

Dr. Kirby Krogstad, Assistant Professor, Department of Animal Sciences, The Ohio State University

Introduction

Energy is in body tissue, organs, and products like meat and milk. A nutritionist’s goal is to direct, or partition, as much energy toward the desired outcome for a particular group of cows. The goal of where to direct energy during lactation may change. The cow’s natural inclination for energy partitioning also changes as lactation progresses. The following quote from NASEM (2021) sums it up nicely:

“Energy partitioning is most affected by stage of lactation but also by the interaction between diet and physiological state of the cows as they progress through lactation.”

In early lactation, cows direct more energy to milk, while in later lactation energy shifts toward body weight gain (Figure 1). Therefore, a skillful nutritionist alters the energy sources and concentrations fed to cows to direct the energy to the desired locale at the desired time.

Figure 1. Cow’s metabolism and energy flow changes during lactation. Strategically using energy sources can maximize milk yield and improve body condition, but the optimal sources depend on the stage of the cow’s lactation. Created in Biorender.com

Energy partitioning is an important part of ration formulation but is not necessarily reflected in ration models. Models like NASEM and CNCPS include requirements for milk production, growth, and pregnancy, but the models do not directly reflect the metabolic shifts within the cow. If you’re diligent, inputting the pregnancy status and target body weight change, then models do partially reflect the changes in energy partitioning as lactation progresses. At this point, understanding how to use energy sources and manage energy concentrations to optimize energy partitioning is a skill requiring proper nutrition model use and knowledge of the cow’s nutritional biochemistry. The latter is what this article strives to describe.

Early Lactation – Step on the Gas!

During early lactation, mammals, not just cows, prioritize milk production. A byproduct of decades of dairy cow nutrition research is a thorough understanding of postpartum metabolism. After calving, there are coordinated changes across tissues that prioritize milk production: the liver increases gluconeogenesis, adipose tissue reduces fatty acid uptake and increases lipolysis, the muscle decreases glucose use and increases protein degradation, and insulin declines; each change prioritizes resource use by the mammary gland for milk production (Baumgard et al., 2017). As a nutritionist, we can use these built-in adaptations to lactation to increase milk yield and profitability.

Promoting the production of milk components in early lactation can be achieved through provision of energy like starch and palmitic acid. One great example of the cow’s ability to take energy from starch and convert it to milk yield was a research project by Maltz et al. (2013). They provided more of the concentrate mix (composed of corn grain, cottonseed, citrus pulp, soybean hulls, and soybean meal) to cows depending on their calculated energy balance. As cows were provided more energy, mostly from more starch, they made more milk. The additional energy in early lactation was not used for body weight or body condition. McCarthy et al. (2015) also observed that feeding 26% starch instead of 21% dietary starch increased early lactation milk yield.

Supplementing palmitic acid can also increase postpartum milk yield. Both Parales-Girón et al. (2025) and de Souza et al. (2021) observed that feeding palmitic acid at 1.5% of diet DM increased milk and milk fat yields after calving. The risk of additional palmitic acid is that body weight loss may also increase. Excess body weight loss can reduce fertility or increase disease risk and should be monitored if feeding palmitic acid.

The risks for feeding both additional starch and palmitic acid can be mitigated with sound ration formulation. First, when feeding additional starch, it is best to avoid highly rumen degradable sources, like barley or high moisture corn, as feeding them may reduce feed intake and milk yield (Albornoz and Allen, 2018). Providing adequate forage NDF (17-27%; NASEM, 2021) or physically effective NDF (20% of diet DM) can also help mitigate risks of increasing dietary starch. The body weight loss when feeding palmitic acid can be reduced by feeding some oleic acid, often in a fatty acid blended product targeting 0.8 or 0.9% of diet DM as oleic acid (de Souza et al., 2021). Feeding high oleic soybeans likely provides a similar benefit.

Later Lactation – Maintain Body Condition

As lactation progresses, a cow’s metabolism shifts. The resources we provide her are not as strongly prioritized toward the mammary gland. It’s also likely, if her lactation has gone according to plan, that she is pregnant and allocating resources to a growing fetus. Her metabolic and physiological changes require changes in dietary substrate to maintain milk production and a healthy body condition.

As lactation progresses, providing dietary starch as an energy source promotes body tissue accretion. Feeding starch in place of NDF and fatty acids increases body weight gain in lactating dairy cattle (Boerman et al., 2015; Morris et al., 2020; dos Santos Neto et al., 2025). This is likely a result of increased propionate which promotes insulin signaling, a pro-tissue building signal in mammals. Feeding digestible NDF as a carbohydrate, instead of starch, generally promotes acetate production in the rumen, not propionate. Acetate does not cause the same insulin response and thus does not promote the same weight gain. In later lactation cows, feeding NDF in place of starch can maintain or sometimes increase milk yield.

Additionally, supplementing palmitic acid may increase milk fat yield while avoiding body weight gain from additional energy in later lactation. The ability of oleic acid supplementation to increase fatty acid digestibility and increase sensitivity to insulin signals increases the risk of excessive body weight gain during later lactation. Thus, oleic acid supplementation should be limited, and palmitic acid should be increased as lactation progresses.

Conclusions

The bottom line is that cows’ needs, and their bodies’ partitioning of nutrients to suit those needs, change as lactation progresses. As nutritionists, we can use those metabolic changes to manage the cows according to our goals throughout lactation. In early lactation, we can strategically provide energy sources, like starch and fatty acids, to maximize milk production. During later lactation, providing digestible NDF sources minimizes body weight gain while maintaining or increasing milk production. Implementing these feeding strategies to both maintain milk production and manage body condition of your cows will increase animal health and production over the course of their lifetime while increasing the farmer’s profitability and efficiency.