I love looking back into my history of feeding cows and seeing things that we simply figured out by trial and error that years later have scientific explanations of why they work. Some good cow sense, a close eye on things like manure evaluation, and monitoring butterfat levels along with a little nerve to push the boundaries of feeding suggestions can be okay if approached with proper care.

In my 30-plus years of feeding cows, I’ve seen ideas and concepts born from trial and error that now have nutrient names and recommendations to go along. I think the best and also most significant one of these is related to the question of how much forage, fiber, and overall roughage is necessary in a lactating dairy ration. Since cows are grazing herbivores by nature, it is obvious that forage is a big deal for them. How much, though, is the right amount?

We know that a 100% forage ration is a good fit for the cow. The cow will likely be happy with this diet and will work hard to chew and ruminate through any number of forages to grow, gestate, lactate, or just maintain. As for the growth and lactation part, this is where the rub comes in. To take this foraging beast and make her economically successful, 100% forage will likely not be the ration of choice.

Since the production of beef or milk requires energy, and we have selectively bred to create animals that have more and more genetic potential to produce, we begin the march down on forage percentage levels to support this production potential. The obvious question is: How low can you go knowing that cow health issues can at some point become a problem?

The shift to dairy

I remember as a beef nutrition grad student in 1989, it occurred to me that I really didn’t know much about dairy cows and milk production. The farm rules of thumb that I grew up with were sorely lacking in dairy info. In my family farm experiences, dairy skipped a generation. So, I remember creating a “cheat sheet” of sorts with some basic dairy info and pinning it on the bulletin board beside my desk. Mind you, this was before Google. I wish I had that sheet now!

The information included items like body weight, expected milk production, and intake, and probably if there was one thing about the diet, it would have been the percent of forage in a typical milk cow diet. In basic dairy nutrition, we were taught that dairy cows needed 40% of their diet dry matter as forage. Soon after, with that information in mind, I unexpectedly made the shift from beef to dairy nutrition. That was 33 years ago!

The big shift in Texas

In the early 1990s in Texas, the dairy scene was in a state of change. There were traditional dairy farms feeding high-starch grain mixes in the parlor with either grazing or some type of free-choice hay in the pen. At the same time, dairy producers moving into Texas were beginning to influence their new neighbors with various steps toward some type of partial or total mixed ration.

With what little amount of ration formulation that could be accomplished using things like grazing and free-choice hay, it was always difficult to really know if that magical 40% forage was being achieved or not. Making cows eat more forage was a bit like leading a horse to water. Making them eat more wasn’t an exact science. Reducing the grain fed in the parlor might help if the forage percent was lower than 40%, but milk loss was a real concern there.

However, when building a diet for the total mixed ration (TMR) fed herd, all of a sudden we could actually mandate the forage percent in a ration. This was a great change and the cows performed better. But was 40% really the optimum level?

I knew that feedlot animals had roughage levels closer to 10%. Was there something to learn there even though there are numerous differences in the type of animal in each production system?

Since forages are nearly always lower in energy density and digestibility than grains, reducing forage can oftentimes elevate milk production. Knowing where to stop is the problem. One of the issues with the old 40% thumb rule is that forage isn’t forage. In other words, all forages are not created equal, not even close! Wheat straw isn’t the same as top-quality alfalfa hay and neither are like corn silage.

The 40% rule

During my early years as a nutritionist, I lived and died by the 40% rule. These were diets in Texas that were based on alfalfa hay and maybe included a few pounds of sorghum and or small grain silage. As I began to experience interactions with nutritionists from the northern dairy regions, their forage percent was dominated by corn silage. I remember when it occurred to me that my 40% forage in Texas was not the same as their 40% or even 50% forage in the Upper Midwest.

Hmm, perhaps I could be including more grain than I had previously felt comfortable feeding. This was a significant change point for me in feeding cows. Since those days, these ideas have been better described in topics and nutrients like peNDF (neutral detergent fiber), forage NDF, and more recently uNDF240. With the use of a Penn State Particle Separator and close attention to manure health, each nutritionist has found what is the sweet spot for each dairy. Each farm is unique due to different qualities of forage, type of forage, chop length of silage and hay, and even the mixer used to prepare the final ration. It all matters!

Since we have mostly focused on forage feeding to this point, it is fair to ask if the balance of the diet impacts the amount of forage and fiber needed. The answer is absolutely yes! In fact, there is more likely a stronger and more important maximum of rapidly fermentable carbohydrates. Thus, if the maximum carbs have been met, and the minimum forage is set from various influences, what makes up the rest of the diet matters as well.

There is probably no better ingredient than soy hulls to fill the gap! If you can’t increase starch and you have decided, or had it decided for you by economics or drought, that your forage percent is on the low end of acceptable, a nonstarch, nonbulky ingredient like soybean hulls will be the solution and can complete that ration.

So, all of that is a nice story, but why does it matter as I feed cows in the summer of 2023? It matters because we are still thinking and fine-tuning what is the right level for each situation of what type of forage to feed to dairy cows. At no time is this more of a question than during the routine intake reduction in the summer.

What should we do with the forage ratio when intakes are reduced? Should we stay the same or maybe go lower to increase energy?

There has even been a suggestion that forage percent should increase if the forage or roughage requirement (if there actually is one) is based on body weight, not intake. There are so many angles here. What is a nutritionist and a dairy producer to do?

The answer is focused on watching the cows.

I have been forced to feed lower forage rations in some areas due to drought. I must say that I have been concerned about this and we have been watching carefully. What the cows have told us is that they are still good. I hesitate to say what forage level I have found to be workable, but let’s just say I would’ve bet against it being okay. The cows are fine, the drought has been survived, and we are a little smarter about what we can do with ration flexibility.

What can I learn from this and apply it during heat stress? Well, as long as I have soybean hulls or something similar to work with, we can carefully track shaker box results, closely watch manure and butterfat and figure it out. I think we can take care of heat-stress cows much better to help summer milk production, reproduction, and cow health. You will find us here, always learning.