If polled, most producers would recognize that forage quality in any ruminant operation is important. When asked to define forage quality, though, answers would start to vary. This is partly because producers have unique goals for their forage program that will define unique quality parameters. Answers can also depend on the crops that are grown. For example, the quality standard for corn silage would differ from that of alfalfa haylage. However, when we take a step back and consider the purpose of forages in our rations, defining forage quality is important because it helps operations set goals to achieve and improve over time.
It’s a common belief that when we maximize tonnage, we must sacrifice quality, but with an improved understanding of crop management, this does not have to be the case. There are many forages capable of producing high tonnage and high quality when managed properly, so developing a forage system that allows for continual improvement can have many benefits. High-quality forage can be fed at higher rates while maintaining performance and swapping out commodities for high forage content can result in ration savings. The optimum result is to create a rumen environment that is advantageous for cellulolytic bacteria to thrive, which increases acetate production to improve overall milkfat production. If we add up all the instances that optimizing for high-quality forage can make an impact, there can be substantial economic savings from decreasing ration costs to improvements in energy-corrected milk.
In our journey to identify what high-quality forage means and capitalize on its benefits, understanding what individual nutrients drive the total digestible nutrient (TDN) value is a key data point. TDN is a summative equation that assesses the content and digestibility of each nutrient to estimate how much energy is potentially available to the cow from a particular feedstuff, allowing us to put a nutritive value to the tons of feed harvested.
Knowing the overall TDN – and how each nutrient and its respective digestibility contribute to it – helps producers identify the factors driving energy value in each forage and make informed decisions. In corn silage, total digestible starch (tdStarch) typically supplies more than half of the total digestible nutrients, making starch digestibility a primary driver of TDN. In contrast, for sorghum or sorghum-sudan silage, total digestible neutral detergent fiber (tdNDF) becomes the major contributor to overall TDN, shifting the focus toward fiber digestibility when evaluating these forages.
While this is largely due to the high overall NDF content in this forage, it emphasizes the importance of maximizing the digestibility of fiber content. For example, the average NDF content of sorghum silage is around 52%. Now, if we multiply that by the 15th and 85th percentile for total tract NDF digestibility (TTNDFD), which are 32% and 50% respectively, the range in tdNDF is nearly 10% (16.6%-26%). Furthermore, for every 10 pounds of dry matter (DM) fed, this equates to 1 pound difference in digestible fiber and TDN with each additional pound of TDN delivered containing enough energy for the cow to produce an additional 3.5 pounds of milk. Even in corn silage where tdNDF is attributing a lower amount to the total TDN, improving TTNDFD by three units, which would represent a move from average quality forage to the 75th percentile, would increase energy by an additional 2%.
Looking at the TDN results is only part of the equation when defining a forage equation. It is also essential to weigh the economic value of these nutrients. Even if a single nutrient contributes the majority to the TDN value, it still may be more cost-effective to obtain it elsewhere rather than focusing forage goals on maximizing that one nutrient. For nutrients like starch and crude protein (CP), assigning an economic value is straightforward because we can use corn grain equivalents to assign a value to starch and protein meal equivalents to assign a value to the CP portion. Conversely, fiber digestibility has not been quite as translatable.
It is a valued resource but numerically it can be tricky to quantify, and we often don’t tease out the true economic impact this nutrient can have. Using high-fiber products to assess the value of fiber digestibility can be used in a comparable way to how corn grain or soybean meal are used for starch and CP, respectively.
The cost of each digestible nutrient per ton of feed can then be calculated if the cost to produce each ton of feed is known. We can take it a step further and find the opportunity cost or cost to bring in equivalent nutrients from an alternative source. Bringing the denominator down to this back to the acre allows for the comparison of the impact of agronomic inputs, or even simply the variable costs of growing different crops, which can be valuable in volatile years, such as this one.
Of course, the real test is how the rumen responds. We must keep biological factors in mind such as purchased dry corn grain may not digest the same as ensiled starch, or alternative fiber from byproducts won’t provide physically effective fiber. These factors can give us insight as to what nutrients and forages to prioritize to ensure forage decisions are as economically robust as possible. For example, because cows have a need for physically effective fiber, limiting resources that restrict our ability to grow forage in near proximity to the feeding operation puts an increased value on this nutrient. So placing an emphasis on ensuring what we produce is not only nutrient dense but also has sufficient tons will help create that winning situation for fiber quality.
Although physiologically the importance of digestible fiber has not changed, several industry dynamics have impacted the importance of digestible fiber from a productivity, sustainability and economic standpoint. From a dairy perspective, increasing operation size, migration and growth of farms in water-restricted areas; sustainability incentives; and increased genetic butterfat potential have all impacted the value of digestible fiber. High beef demand has fueled high beef prices alongside drought, and increased land competition has changed the feed dynamics for beef producers. Regardless of the operation or forage quality goals, aligning management practices to support high fiber digestibility alongside tonnage will help farms capitalize on many fronts.
A final consideration that is becoming more common is the resource constraints to forage production. In traditional circumstances, it may be economically advantageous to grow starch rather than purchase, but if water is limited, we may not have the resources available to produce high starch levels. Conversely, if water is allocated to starch, we may not have as much available to produce other forages, decreasing our harvested tons of TDN overall. Also, as farm size grows, feed must be sourced or grown in a larger radius surrounding the operation. This leads to longer hauling distances for some feed, which can impact the overall cost of the feed, resulting in a need to increase the energy density to help offset increased costs per unit of TDN.
While no two operations are the same or have identical goals, forage is a key component in maximizing economic opportunity. From decisions about what to plant and how to manage it to growing or sourcing components in a ration, setting clear goals while balancing the economics of these decisions can feel overwhelming. Taking the time to assess total digestible nutrients harvested as it relates to agronomic costs can provide simplicity to this complex problem.
