Enhancing Ruminant Health
For more information 1-800-265-8335
For more information 1-800-265-8335

Sugar vs Starch: Understanding the Difference in Dairy Cow Rations

Sugar vs. Starch: Understanding The Difference in Dairy Cow Rations

Starch in Lactating Dairy Cow Diets 

About 70% of lactating cow diets are made up of carbohydrates, ~30% of these carbohydrates consist of starch. Traditional supplements to silage, include concentrates from grain, whether mixed in the ration or provided directly in automated milking systems during milking, are high in starch. Starch is an effective way to supplement energy to dairy cows and support cow maintenance and milk production. However, problems arise when too much starch is fed in cow diets.  Commonly, producers will feed fresh cows higher amounts of concentrates to try and compensate for the energy demands associated with milk production in early lactation. Starch is rapidly fermented in the rumen, but feeding high amounts to dairy cows can increase the risk of a depressed rumen pH (causing the rumen to become acidic). This can further lead to the development of a metabolic disorder known as subacute ruminal acidosis (SARA). This condition is caused when a large amount of grain (starch) is fermented in the rumen into volatile fatty acids (VFAs).  SARA can have major consequences for the cow including depressed feed intake, reduced milk yield, fluctuating DMI, as well as possible gastrointestinal damage, lameness, and liver abscesses. This disorder affects 20-30% of early to mid-lactation dairy cows in North America, although more subtle symptoms may mean that SARA goes underestimated in many herds (Vitti, 2020). The economic loss associated with SARA has been estimated to fall within the range $400-475 per cow/year.

Sugar in Lactating Dairy Cow Diets 

One way to enhance DMI and lessen the risk of ruminal acidosis through the diet is to increase the proportion of sugar in the diet. Sugar, in particular molasses, is known to be very palatable and has the potential to improve rumen function and health. Sugar can also provide energy to the ruminant without increasing the risk of SARA. Sugars have different pathways of digestion than starch.  One theory is that increasing dietary sugar supply increases the microbial protein pool and increases the rate of passage through the rumen, decreasing the organic matter that is available for fermentation and acid production. Another potential explanation is that sugar can be utilized by the microbes for glycogen synthesis, allowing the sugar to be converted and stored as a short-term energy source when needed. This would temporarily reduce fermentation and acid production in the rumen, potentially contributing to higher rumen pH. Sugar supplementation also supports microbial growth, particularly for fiber-digesting bacteria, speeding up fiber degradation and allowing for greater DMI and rumination. Recent research done by the University of Guelph has even shown that supplementing sugar in dry cow diets can be beneficial to the animal, as it encourages and maintains DMI in the weeks leading up to calving, further improving metabolic health post-calving as well.


Sources of Sugar 

Sugar can be found in various concentrations across many components commonly fed in dairy cow rations. Fresh hay and forages for example, will have a reasonable amount of sugar, especially compared with fermented silages which will have lower concentrations of sugar due to the fermentation process during ensiling. Other common ration by-products such as beet pulp, citrus pulp and bakery waste will have moderate-high sugar concentrations with liquid whey and liquid molasses offering the highest sugar concentrations. Molasses and whey are commonly found in various commercial liquids feeds. However, molasses is more durable and affordable compared to liquid whey and is thus the most common method used within the dairy industry for supplementing sugars to cows. 

Concentrations (% DM) of Carbohydrates in Feeds1





Alfalfa (fresh)




Alfalfa silage




Bakery Waste




Citrus Pulp




Sugar Beet Pulp




Corn Grain




Corn Silage




Molasses, Cane








1Data in this table was adapted from “Feeding Sugar to Ruminants,” MB Hall (http://www.extension.org/pages/25322/feeding-sugar-to-ruminants) from research based out of the department of animal sciences at The University of Florida.


Dairy cows do not have starch requirements in their diets, however, they do have energy requirements. While starch is high in energy it does not necessarily mean it is the only or most efficient way to supplement energy to our dairy cows. Supplementing sugars to dairy cows however, appears a safe and effective way to supplement energy without increasing the risks of SARA and other associated metabolic diseases. Many studies have investigated ways to reduce starch usage in dairy rations and research has shown that limiting and substituting starch with sugar does not negatively impact production or component yields. In fact, studies from the University of Guelph and Michigan State University found that milk production increased while supplementing cows with sugar and also observed better metabolic health during the fresh period. Understanding how to effectively supplement our cows with energy is so important, but understanding the long and short term effects of a given supplement (and the appropriate concentration required) is equally, if not more, important. While starches do not need to be eliminated from lactating cow diets, they do need to be refined and reduced. Replacing concentrations of starch with sugar, by feeding molasses, is an effective way to supplement energy to lactating dairy cows and support the overall health, welfare and nutrition requirements of the cow throughout her lactation.


Hall, M. B.  2019. Feeding Sugars to Ruminants. Dairexnet: Dairy Cattle Extension. https://dairy-cattle.extension.org/feeding-sugar-to-ruminants/ 

Vitti, P. 2020. Living with SARA in the dairy barn. Ontario Dairy Farmer.