Forage selection is one of the most important decisions in dairy cow nutrition. Beyond supplying fiber, forage sources influence rumen fermentation, nutrient utilization, milk composition and the economics of the feeding program.
Among the most widely used forage ingredients in dairy diets, alfalfa hay and corn silage provide different nutritional characteristics that can complement one another.
But what happens when the proportion of these two forages changes substantially?
A new study published in the Journal of Dairy Science investigated how different ratios of alfalfa hay and corn silage affect milk production, milk components, feed efficiency and rumination behavior in lactating Holstein cows.
The results suggest that increasing alfalfa inclusion does not necessarily improve productive performance. Instead, a more moderate proportion of alfalfa within the forage component may provide advantages for certain milk composition and nitrogen-related outcomes.
KEY RESEARCH FINDING
In diets containing 62% forage on a dry matter basis, a forage mixture of approximately 30% alfalfa hay and 70% corn silage was associated with favorable milk true protein production and lower milk urea nitrogen. Dry matter intake and energy-corrected milk yield did not differ significantly among the five dietary treatments.
Why the balance between alfalfa and corn silage matters
Alfalfa and corn silage are valuable forage ingredients, but they contribute different nutrients to dairy cow diets.
Alfalfa hay is generally valued for its protein content, fiber characteristics and contribution to the mineral supply of the ration. Its nutritional value can vary according to maturity at harvest, growing conditions, conservation and processing.
Corn silage, meanwhile, provides fermentable carbohydrates through its starch and fiber fractions, making it an important source of energy in many dairy feeding systems.
Combining these forages allows nutritionists to balance nutrient supply while considering rumen function and milk production objectives.
However, changes in forage proportions can also influence dietary fiber characteristics, fermentable carbohydrate supply and the synchronization of nutrients available to rumen microorganisms.
This makes the optimal ratio more complex than simply increasing the inclusion of whichever forage has the highest individual nutritional value.
Researchers evaluated five forage combinations
The study, conducted by researchers associated with the William H. Miner Agricultural Research Institute, Cornell University and Forage Genetics International, included 105 Holstein cows.
Of these, 45 were primiparous cows and 60 were multiparous cows.
Animals were enrolled in two groups and assigned to one of five experimental diets using a randomized complete block design. The study included a one-week baseline period followed by four weeks of experimental feeding.
All diets contained 62% forage on a dry matter basis, with the forage fraction consisting of different proportions of chopped alfalfa hay and corn silage.
DIETARY TREATMENTS
| Treatment | Alfalfa hay | Corn silage |
|---|---|---|
| 10ALF | 10% | 90% |
| 30ALF | 30% | 70% |
| 50ALF | 50% | 50% |
| 70ALF | 70% | 30% |
| 90ALF | 90% | 10% |
Percentages represent the composition of the forage fraction, not the entire diet. Forage accounted for 62% of dietary dry matter in every treatment.
The diets were formulated to provide similar metabolizable energy and protein supplies, allowing the researchers to examine how changing forage proportions influenced the measured responses.
However, analysis of ingredient samples after the experiment revealed that metabolizable protein supply increased across the dietary treatments as alfalfa inclusion increased.
This difference is important when interpreting the results because the diets were not perfectly equivalent in their analyzed metabolizable protein supply.
Milk yield and feed intake remained relatively stable
One of the notable findings was the absence of significant dietary effects on several major performance indicators.
Changing the proportion of alfalfa hay and corn silage did not significantly affect:
- Dry matter intake (DMI)
- Energy-corrected milk (ECM) yield
- Energy-corrected milk production per unit of dry matter intake (ECM/DMI)
This indicates that cows maintained broadly comparable overall intake and energy-corrected milk production across the evaluated forage combinations during the experimental period.
For nutritionists, this is relevant because it suggests that substantial changes in the relative proportions of these forages may be possible without necessarily producing major differences in these particular performance outcomes, provided that the complete diets remain appropriately formulated.
Nevertheless, similar ECM production does not mean that all aspects of milk composition and nutrient metabolism responded identically.
A moderate alfalfa inclusion favored milk protein production
Although energy-corrected milk yield did not differ significantly, the study identified important responses in milk components.
The 30ALF treatment, containing 30% alfalfa hay and 70% corn silage within the forage fraction, produced the most favorable response for milk true protein yield among the combinations evaluated.
This finding is relevant because milk protein represents an important component of milk value in many dairy payment systems.
Increasing milk protein output without a corresponding increase in feed intake could be economically meaningful, although the study did not establish a universal economic advantage for the 30ALF diet.
MORE ALFALFA DID NOT MEAN MORE MILK PROTEIN
The greatest improvement in milk true protein yield occurred with the 30:70 alfalfa-to-corn silage mixture, rather than with the highest alfalfa inclusion levels. This highlights the importance of evaluating the complete ration instead of focusing on the nutrient contribution of a single forage.
Changes in milk fatty acid composition
The researchers also evaluated the fatty acid profile of milk, including the concentration of de novo fatty acids.
These fatty acids are synthesized primarily within the mammary gland from precursors generated through rumen fermentation and are commonly studied as indicators of aspects of mammary lipid synthesis and nutrient metabolism.
The 30ALF diet was associated with the most favorable response in de novo fatty acid concentration.
This observation suggests that forage composition may influence milk fat synthesis-related outcomes even when energy-corrected milk production remains relatively stable.
However, de novo fatty acid concentration should not be interpreted on its own as proof of superior overall rumen health or greater total milk fat yield.
Milk urea nitrogen was lowest with the 30ALF diet
Another important result involved milk urea nitrogen (MUN), which was lowest in cows receiving the 30ALF treatment.
MUN is commonly used as an indicator related to nitrogen metabolism and the balance between dietary protein supply and nutrient utilization.
Elevated MUN concentrations can occur when nitrogen supply exceeds the animal’s capacity to utilize it efficiently, although MUN is also influenced by factors such as energy supply, feeding management and physiological conditions.
The lower MUN observed with the 30ALF diet may therefore suggest a more favorable nitrogen-related response under the conditions of this experiment.
However, the researchers did not establish that this treatment directly reduced total nitrogen excretion or environmental emissions.
Lower milk urea nitrogen may indicate a favorable response in nitrogen metabolism, but it should not be treated as a direct measurement of nitrogen-use efficiency or manure nitrogen losses.
More alfalfa was associated with less rumination time
One of the most interesting behavioral findings involved daily rumination.
The researchers observed a linear decrease in rumination time as alfalfa hay progressively replaced corn silage.
Rumination plays an important role in ruminant digestion by promoting feed particle breakdown and saliva production, which contributes to buffering conditions within the rumen.
However, rumination time is influenced by several dietary characteristics, including forage particle size, fiber properties, feed processing and overall ration composition.
The reduction in rumination time therefore does not automatically indicate poorer rumen health.
Instead, it suggests that the physical and nutritional characteristics of the forage mixtures affected chewing behavior.
Importantly, the study did not report a corresponding reduction in energy-corrected milk production as alfalfa inclusion increased.
What does this mean for effective fiber management?
The findings illustrate why evaluating dietary fiber requires more than considering forage inclusion percentage alone.
Although all experimental diets contained the same overall forage proportion, their composition differed substantially.
Different forage sources contribute distinct fiber characteristics and physical properties, which may influence rumination and rumen function.
For nutritionists, this reinforces the importance of considering:
Forage particle size
The physical structure of the ration and its potential influence on chewing and rumination.
Fiber composition and digestibility
Differences in neutral detergent fiber characteristics and the extent to which forage fiber can be utilized.
Fermentable carbohydrate supply
The contribution of starch and other carbohydrates to rumen fermentation and energy supply.
Whole-ration nutrient balance
Interactions between forage ingredients and the concentrate portion of the diet.
These considerations are practical implications of the findings rather than additional treatment effects directly established by the study.
Is 30% alfalfa and 70% corn silage the ideal combination?
Based on the outcomes measured, the researchers identified an approximate 30:70 alfalfa-to-corn silage ratio as a favorable combination within the 62%-forage diets evaluated.
However, this does not establish a universal optimum for all dairy farms.
The study involved a specific population of Holstein cows, a defined ration structure and a four-week experimental feeding period.
Different responses may occur when forage quality, dietary forage inclusion, cow production level, stage of lactation or management conditions differ.
Furthermore, the most appropriate forage combination will also depend on non-nutritional considerations such as forage availability, production costs, storage capacity and local growing conditions.
IMPORTANT INTERPRETATION
The study supports an approximate 30:70 ratio within the forage fraction of the diets tested. It does not recommend that 30% of every dairy cow’s total diet should consist of alfalfa hay, nor does it establish the same ratio as optimal across all production systems.
Practical implications for dairy producers and nutritionists
The research provides useful insights for farms evaluating the relative inclusion of alfalfa hay and corn silage.
First, the absence of significant differences in dry matter intake and energy-corrected milk production suggests that considerable flexibility may exist in forage combinations when diets are adequately balanced.
Second, the differences in milk true protein, de novo fatty acids and milk urea nitrogen demonstrate that milk composition and nitrogen-related responses can vary even when overall production remains similar.
Third, the rumination findings emphasize the importance of considering physical forage characteristics and feeding behavior alongside conventional nutrient concentrations.
Finally, decisions should be based on the nutritional characteristics of the forages actually available on the farm rather than assuming that one forage source will consistently outperform another.
Finding the right balance, not simply increasing forage quality
Alfalfa hay and corn silage remain complementary ingredients in dairy cow diets, but their optimal proportions depend on the broader nutritional and management context.
This study demonstrates that a moderate inclusion of alfalfa hay may support favorable milk component responses without changing overall energy-corrected milk production.
At the same time, the findings illustrate why ration formulation should consider milk protein production, nitrogen-related indicators, rumination behavior and farm-specific economics rather than relying on a single measure of performance.
The most effective forage combination is not necessarily the one containing the greatest proportion of alfalfa or corn silage. It is the one that best aligns nutrient supply, milk production objectives, rumen function and the practical conditions of the dairy farm.
For dairy nutritionists, the findings reinforce a central principle of precision feeding: the nutritional value of forage ingredients is best understood through their contribution to the complete diet.
Source
Morrison, S. Y., Zang, Y., Weakley, D. C., Chase, L. E., Dann, H. M., Ballard, C. S., & Grant, R. J. (2026). Effect of diets differing in ratio of alfalfa hay and corn silage on lactational performance and rumination of Holstein dairy cows. Journal of Dairy Science. Published online September 3, 2026.