Today’s U.S. dairy industry is built on hard work, determination, a love for cows, and corn silage. In my early years as a dairy nutritionist in central Texas in the 1990s, things were different. My rations revolved around alfalfa — and lots of it. Hay trucks were burning up the road between the high country of Colorado and bustling and rapidly growing dairies in Stephenville, Texas.
In those days, we used four-auger horizontal mixers, and the bunks were dark green with Colorado alfalfa hay. The bunks were, well, pretty long and hairy, and yes, sortable. But it was what we had to work with. I know there are geographies in the U.S. where alfalfa hay still reigns as the king of forages, but I expect if you were to look at the percentage of milk produced on corn silage-based diets, you might say the king has been dethroned and the queen is now in charge. I wonder, though, if the princess is eyeing the throne in some geographies where water is a limiting factor for milk production. More on that to come. For now, back to the reigning queen.
I have the opportunity to formulate, collaborate, and review dairy diets from across the U.S. and occasionally around the globe. If there was one commonality in many of these, it is that plus or minus 20 pounds of corn silage seems to more and more commonly be the base of these diets. In round numbers, that is nearly 40% of the ration dry matter intake. No other ingredient approaches that level of dominance, and thus, nutrient supply to the animal. It is this dynamic that results in discussions about corn silage dominating everything from research projects and journal articles to images of corn silage analysis lab reports on Facebook, along with a plethora of entertaining corn silage harvest clips on TikTok and Instagram. Face it, our industry is obsessed with corn silage, and rightfully so.
If you’ve ever considered producing milk in some dystopian and post-apocalyptic world and you could have only two ingredients to feed dairy cows, you had better pick corn silage and soybean meal. So, if you milk cows somewhere that corn silage is a good agronomic option for you, it is probably the best path forward. Focus all your effort on growing good corn silage and the rest of the diet, with a great deal of flexibility, will sort itself out.
When we feed corn silage in a high-producing lactation ration, we really do so to accomplish two main things. First, because of the way the cow is designed as a ruminant, we need roughage to keep her in good healthy shape. Secondly, the starch in corn silage makes magic happen in the rumen. Fermented starch drives so many positive things in the rumen, and when correctly formulated, it is a bit like the soul of the diet.
When going to the next level of detail for this roughage and starch, we look at various fiber considerations in the lab to be sure that not only does that chopped up cornstalk scratch the rumen, but it also needs to be fermented to create the building blocks for milkfat. Likewise, the starch in the kernel must be available for fermentation in the rumen to make the magic happen. For this measure, we can’t seem to decide what is best, but some form of a ruminal starch rate is what we need to formulate well. Be sure that things such as kernel processing, good packing, and covering are all accomplished with expert skill.
Pinpoint protein
Now, shift gears from our corn silage banter to the tag on a bag of calf feed, show feed, or even your dog food bag nutrient specs. What nutrient is at the top of that list? Crude protein of course. In fact, in the world of feed and forage, crude protein content is the common descriptor for all quality assessments of a feed or forage. Think about the ever improving high-protein dog food race. What was once 20% is now 25%, and if you want your dog to be truly at the top of its game, it is recommended to feed a 30% high-protein, premium dog food. It is the same with hay. No matter if you are buying hay for 10 beef cows on your rural palatial ranchette, or hay for the bag in the stall of your million-dollar racehorse, you probably bought the hay as 10% or maybe even 12% protein. The chances of knowing the fiber, sugar, or ash levels in that hay are low. So, why don’t we talk more about the protein level in corn silage?
Perhaps it is because starch and fiber take up all the oxygen in the room. From different points of time for fiber digestion and trying to best understand rate curves on starch fermentation, there seems no time for protein. How important is it? The model can help us with that.
If grass hay is sold on protein content at the feed store, corn silage is sold primarily on starch content. The inverse for starch in the corn plant is fiber, and we characterize the fiber quality nicely via several time points of fiber digestibility. Protein, in this case, is less complicated and the range in corn silage is not as wide. Perhaps it is only two to three points, ranging from 7% to 10%. Though not wide, when you feed in excess of 20 pounds of dry matter (DM), this is no small detail. If you feed 2 pounds of corn gluten feed and you know the protein commonly ranges from 16% to 20%, at the low feed rate, it is less critical. If corn silage fed at 40% of the ration DM goes from 7% to 9%, you better pay attention.
I ran a quick optimization to see what the feed cost impact was of a two-point move in corn silage protein; from 7% to 9%. I used a current real-life ration that included 22 pounds of corn silage in 55 pounds of total intake. I first created a 7% and 9% protein corn silage with the other nutrients the same. The corn silage in the real ration had a cost of $60 per ton at 30% DM. The 7% CP corn silage had a shadow value of $57.27, and the 9% corn silage was equal to the one actually in the diet at $60. This difference of $2.73 as fed seems more meaningful when considered on a 100% DM basis at $9.10 per ton. That is a sizable difference per ton for something you feed at 22 pounds of DM. When using the same linear optimization process to use each of these to support the same milk, I, in fact, repeated the approximate 10 cents cost difference per cow for the different protein levels.
In summary, you and I both need to call in our agronomy advisers to help us understand what we need to do to make sure we maximize protein level in corn silage. It may be variety driven, timing, amount and form of nitrogen fertilization, or perhaps an added complication to the decision of when to harvest corn silage. We will let the experts in that world advise us, but the message is clear. Don't forget about the protein level in your corn silage; it matters!
