The author is president of the William H. Miner Agricultural Research Institute, Chazy, N.Y.
Feed costs — especially corn grain — have risen substantially this year. Maximizing the nutritional value of homegrown forages is always a top priority for profitable dairy farming, but in high feed cost years, it becomes absolutely essential.
On many U.S. farms, corn silage is a predominant forage. The corn harvest for silage will be completed for many of you when this article is read. Hopefully, it was chopped at the correct dry matter content and theoretical length of cut and packed and covered well.
Now the focus turns to feeding corn silage to optimize the herd’s intake and milk yield response. Many farms have a variety of corn hybrids that are often segregated into different silos: brown midrib, leafy, or other hybrids that differ in content of neutral detergent fiber (NDF), starch, or digestibility. One fundamental decision concerns cow grouping and targeting corn silage to cows that will respond best to varying carbohydrate content and digestibility.
Cows and fiber digestibility
Nearly two decades ago, Michigan State University researchers summarized the published data and calculated that a one percentage-unit improvement in forage NDF digestibility was associated with a 0.40 pound per day gain in dry matter intake and a 0.55 pound per day increase in 4% fat-corrected milk. Importantly, this relationship seemed to hold for many types of forages regardless of how NDF digestibility was measured.
Unsurprisingly, the researchers noted that high-producing cows had more substantial responses in both dry matter intake and milk yield when compared to lower-producing cows as it relates to improved forage fiber digestibility. Gains in fat-corrected milk yield varied from 0 to nearly 2 pounds per day for each percentage unit increase in fiber digestibility, as cows ranged in milk production from 70 to 120 pounds per day.
High corn silage diets
More recently, University of Minnesota researchers combed the literature for studies that specifically fed higher levels of corn silage. When diets contained more than 40% corn silage on a dry matter basis, cows responded to a one percentage unit increase in NDF digestibility with 0.26 pounds per day more dry matter intake and about 0.30 pounds per day more fat-corrected milk.
So, even though the relationship between NDF digestibility and intake and milk yield varies somewhat among studies, it is clearly positive and one that needs to be taken advantage of when feeding corn silage. This would be especially true for producers who want to feed brown midrib corn silage to the greatest advantage.
The cow’s feed intake and milk yield response to fiber and starch digestibility changes with milk production level. High-producing cows need greater digestibility of dietary carbohydrates, specifically more digestible NDF and starch. Lower-producing, later-lactation cows require less total carbohydrate fermentability in the diet. For this group, diets with more digestible NDF and lesser amounts of digestible starch optimize milk production. In fact, for lower-producing cows in later-lactation feeding, too much highly fermentable starch can reduce dry matter intake and milk yield while elevating body condition.
Recognizing this effect of milk production level and stage of lactation on how cows respond to NDF and starch digestibility, researchers at the University of Nebraska assessed cow response to two corn silage hybrids that differed by nine percentage units in 48-hour NDF digestibility. Cows in this study ranged in milk production from 30 to 122 pounds per day. When switched from a ration with lower NDF digestibility to one with a higher NDF digestibility, cows fell into three distinct outcome groups based on their energy-corrected milk production response.
First, the higher-producing cows — those above about 70 pounds of energy-corrected milk per day —responded positively in milk yield to the higher NDF digestibility. This production response makes sense given the previous work at Michigan State.
In contrast, many lower-producing cows did not respond at all in milk yield to the greater NDF digestibility of the corn silage in the ration. In other words, a producer would be squandering the feeding value of their higher quality corn silage by not targeting it to the high cows.
Finally, a third group of lower-producing cows actually responded negatively in milk production to the higher NDF digestibility corn silage in the ration. Too many producers and nutritionists neglect this group of cows when formulating diets.
So, for several reasons, feeding highly digestible corn silage to low-producing cows can be a worst-case scenario regarding profit and wasted feeding potential. The basic cow response is explained by what we know about how cows respond physiologically to ration carbohydrate digestibility as they move from early to later stages of lactation.
High-yielding cows respond
A study that we conducted at the Miner Institute compared brown midrib corn silage to high-quality grass silage for cows ranging from late-lactation and lower milk production to earlier lactation and higher milk production. Similar to the Nebraska work, we observed that higher-producing cows did much better with the brown midrib corn silage than the grass silage. High-quality grass silage can work well for early lactation cows, but it must be harvested early before NDF content becomes too high and NDF digestibility suffers.
In contrast, lower-producing cows produced more milk when fed high-quality grass silage. Once again, we noted a group of later lactation cows that dropped in milk yield when fed brown midrib corn silage rather than grass silage.
The take-home conclusion was that we need to target forages to appropriate cow groups to realize the full feeding value of the corn silage. With this nutritional information, we can do a much better job of formulating corn silage-based diets for cows in later lactation to avoid reductions in milk. Corn silage with greater NDF and starch digestibility is usually best targeted to high-producing cow groups.
Get the most from silages
We need to think about how we allocate corn silage of varying quality to groups of cows. Higher-producing cows will respond to greater forage carbohydrate digestibility, but lower-producing cows often will not. Once the corn silage has been properly targeted to cows that will respond positively, then we can focus on optimizing ration formulation for intake and milk production.