Alfalfa and corn silage account for a big portion of ration dry matter (DM) in dairy cow diets, especially in the Upper Midwest. As dairy producers evaluate the economic, agronomic and nutritional demands on their farms, they ask, “How can I make best use of my acreage for the greatest return on investment?” That question challenges farm consultants to rethink traditional approaches.
The ‘why’ behind a traditional approach
Alfalfa and corn silage are quite different in their composition, and that’s what makes them complementary to one another in the ration. Their combined crude protein, digestible fiber and readily fermentable starch contents can be used to optimize rations for healthy rumen function, optimal microbial protein synthesis and high levels of energy-corrected milk (ECM) production.
Alfalfa silage offers higher protein content and a faster neutral detergent fiber (NDF) digestion rate that can contribute to a faster rumen turnover rate. However, its higher amount of undigestible NDF (uNDF) due to its higher lignin content contributes to a lower amount of potentially digestible NDF (pdNDF).
Corn silage is considered an energy-dense forage source and can contain moderate to high amounts of readily fermentable starch. It is lower in protein than alfalfa and has the potential to harbor more mycotoxins that may cause immune, rumen and reproductive issues.
Corn silage is similar to alfalfa in terms of total NDF content, but it has lower uNDF. While this difference in uNDF makes corn silage a better source of digestible fiber, its fiber fraction digests slower than alfalfa. A combination of a faster fiber digestion rate (from alfalfa) and slower fiber digestion rate (from corn silage) can keep the rumen pH and rumen passage rate more consistent.
This is why we typically use some combination of alfalfa and corn silage in dairy diets, although ratios can range from 20% alfalfa and 80% corn silage on one farm to 80% alfalfa and 20% corn silage on another.
What is the ‘right’ ratio, then?
Nutritionists will remind you that cows do not have a requirement for alfalfa or corn silage. They have requirements for nutrients that forages, grains, byproducts and other ingredients bring to the ration. The challenge is finding the best economic balance among all the feedstuffs available to the farm.
In recent years, we’ve seen producers reduce the amount of alfalfa in their rations for several reasons. One major reason is ever-increasing land prices as the competition to purchase available acres increases. Dairy producers are looking for ways to maximize their acres from harvest to the bulk tank. To do so, producers must analyze potential yield, management requirements and impacts their forages can have on the bottom line.
Alfalfa tends to positively impact soil health and yield of the subsequent crop planted on the same field, which can reduce input costs (i.e., less applied nitrogen). Depending on the growing season, alfalfa generally yields 4 to 5 tons of DM per acre per year.
Harvest cost, time, weather and soil management can be hurdles that producers have to overcome with an alfalfa crop. Hitting the correct window with sunny and dry conditions to harvest at the correct DM can be difficult. Alfalfa is usually harvested three to five times during the growing season to produce high-quality feed. This intense harvest schedule can consume a lot of time, manpower and cost. While the machinery used to harvest is getting more efficient, it is also getting bigger and heavier and has the potential to cause soil compaction by driving over the same fields multiple times throughout the season, thus decreasing the soil health benefits of an alfalfa crop.
Climate also can be a challenge when dealing with alfalfa. Harsh winters can wreak havoc on alfalfa in the Upper Midwest, killing it off or drastically reducing yields the following year. Intense heat and lack of moisture in the southern U.S. can greatly impact yields as well as fiber quality.
Corn silage is attractive to producers due to its high yield and comparatively simpler, single harvest and its potential to yield 8 tons of DM or more per acre per year. Regions of the U.S. with longer growing seasons have the potential to double-crop with corn silage.
However, weather, input costs and soil health are potential challenges that producers should consider. Corn requires higher amounts of nitrogen application to improve yields, which can quickly increase input costs. Although it’s only harvested once in a year, unpredictable weather conditions in the fall can cause stumbling blocks. Muddy and cool conditions can cause increased wear on equipment and ruts in the field. Both issues will need to be addressed before next year’s crop and will add costs to the bottom line.
Managing for productivity
Once off the field and in bunkers, silos, bags or piles, both alfalfa and corn silage come with management pros and cons. Producers and nutritionists must look at inventories to strategically allocate feeds to make best use of their nutrients. Heifers, dry cows and lactating cows have different nutrient requirements. Differing amounts of each forage can be targeted to these groups so that correct nutrients are reaching the right group for maximum productivity and profitability.
Consistency is also critical when determining a farm’s forage-feeding strategy. Because alfalfa is harvested multiple times per growing season, its nutrient profile can vary greatly based on climate, harvest schedule and handling. On the flip side, corn silage is harvested once per year in the fall and is typically stored in large quantities, generally making it a more consistent forage from beginning to end.
A keen eye on both inventory and ration consistency can be extremely helpful to producers and nutritionists. By knowing what feed you will allocate to each group throughout the year, you can set the ratio of alfalfa to corn silage early and only make subtle changes as you go. This provides cows a consistent diet without major swings in composition and nutrients.
Improvements in corn hybrids have made the transition to high-corn-silage diets (i.e., greater than 70% on a DM basis) more attractive. Corn silage can contain upward of 40% starch on a DM basis. This decreases the need to feed ground corn and makes room for lower-cost byproducts, such as soyhulls and corn gluten feed. These byproducts often provide highly digestible fiber and help keep the rumen at a more stable pH while supplying cows with calories for increased milk production.
In recent years, grasses have also gained in popularity – especially in the Upper Midwest. Grasses bring higher amounts of pdNDF than alfalfa and tend to survive the harsh winters better. They can also fit well in the farm’s nutrient management, as producers can apply manure as fertilizer between cuttings to maximize yield and nutrient potential.
In the end, we need to consider the nutrient requirements of all groups in the herd and then develop a forage strategy that makes best use of available acres to ultimately have the best effects on the bottom line. That’s no small feat. When deciding how to meet your operation’s needs and goals, seek input and resources from your nutritionist, agronomist and financial adviser to explore the multitude of options available and determine the most profitable strategy.
