The author is an assistant professor of animal science at Iowa State University.

High-forage diets for dairy cattle are becoming more popular due to the cost-effectiveness of homegrown forages and potential benefits on milk components. In a 2017 survey, feed industry professionals reported that 91% of their dairy herds had elevated the level of forage they fed in the previous decade or so.

However, if you look for “high-forage dairy diets” in your internet search engine of choice, you will find little agreement on what actually constitutes a high-forage diet. To confuse the issue further, even though corn silage contains the corn grain in addition to the leaves and stem, it is considered 100% forage; thus, high-corn silage diets are considered by most people to be high-forage diets.

No debate here

While nutritionists may argue among themselves about what exactly makes a diet “high forage,” it is clear that dairy producers are increasingly inclined to push for higher forage inclusion in their rations. The neutral detergent fiber (NDF) and NDF digestibility of forage sources will determine how much can be included in the diet.

Forages with lower NDF can be incorporated at greater levels, so forage NDF is a more useful descriptor than the percent forage in the ration. Forages with more digestible NDF will allow for a higher percent forage in the ration as well. Undegradable NDF has been shown to have a strong negative correlation with dry matter intake (DMI).

A number of factors influence the quality of a forage as it relates to NDF and NDF digestibility, including plant genetics and maturity. One of the obvious realities of growing forages is that for every acre of high-quality, fourth-cutting hay that is produced, there may be an acre of lower quality first, second, and third cutting hay. These could still be excellent forages for replacement heifers, dry cows, or low-producing cows.

Even in high-producing cow diets, there can be a time and a place to feed less digestible forage NDF sources. For example, diets based on brown midrib (BMR) corn silage or other very digestible forages may benefit from these less digestible forages to slow down passage rates.

Consider other options

As ruminants, dairy cattle are able to convert forage biomass that would not be available for human digestion into high-quality milk protein. Although our discussion so far has focused on traditional forages such as corn silage, there are a number of alternative forages that provide holistic benefits to the farm as a system that can be successfully incorporated into dairy rations. These include cover crops and cocktail mixes as well as biomass crops.

Typically, biomass crops such as switchgrass will favor quantity over quality of forage production. They provide benefits to soil health and can often be grown on marginal land, but as discussed above, the lack of digestibility can limit how much is included in lactating cow rations. Producers may consider feeding some of these forages to dry cows or heifers, possibly replacing straw in the diet.

Alternatively, cover crops may provide more digestible forage NDF compared to biomass crops. Cocktail mixes can allow the producer to mitigate some of the risks of homegrown forages by mixing forages that thrive under different conditions, such as drought or wet weather.

Three important steps

While there are certainly benefits to feeding high-forage diets, proper management is required for their success in a feeding program. Here are some keys to effectively feeding high-forage diets:

Inventory. In addition to the ration simply containing more forage, it is not uncommon to observe an improvement in DMI. Producers will need the space to store this extra feed inventory.

Stocking density and grouping. Due to their physical characteristics, forages take longer for a cow to consume than concentrate feeds. As a result, cows will likely need to spend more time at the feedbunk. In overstocked pens, this can be especially challenging for more submissive cows that will now have even less available bunk time to spend eating while boss cows dominate the feeding area. If possible, first lactation cows should be grouped separately so that they do not need to compete for bunk space with larger, mature cows.

Feed availability. As a result of these changes in feeding behavior, it is especially important to ensure that cows have feed available for as many hours of the day as possible. Make sure that feed is being pushed up frequently and consistently.

Observe your cows

When making the switch to a higher forage ration, it is critical to observe what the cows are telling you about their new diet. Keep an eye on these indicators:

Dry matter intake. Intake may increase or decrease when moving on to a higher forage diet. If the ration is balanced on high-quality forages, DMI may increase, and feeders will have to keep up with the new demand. Alternatively, high amounts of undegradable NDF may limit DMI.

Cud chewing and rumination. We expect high-forage diets to promote rumination, which can be observed visually by noting how many cows are chewing their cud when resting or measured by using sensor technology. If there is inadequate rumination, cows may be sorting.

Manure consistency. What comes out the back of a cow is a fantastic indicator of what is happening in its rumen and hind gut. In addition to manure scoring, pay attention to what is actually in the manure. Are you seeing forage particles, pieces of corn or whole corn kernels, or mucin casts? These could indicate problems with digestion, including passage rates that are too high or inadequate starch digestion.

Milk components. Cows with happy and healthy rumens produce higher milk components. When moving to a higher forage diet, milkfat should either stay the same or increase. If milkfat drops — and you have ruled out a seasonal effect — it is likely that the particle size of the total mixed ration (TMR) has deviated from a moderate ideal. It could mean that particles are too fine or that they are too long, allowing cows to sort against the forages.

A novel monitoring tool that can be used as an indirect but useful indicator of rumen health is de novo fatty acids. High levels of de novo fatty acids in milk are suggestive of good fermentation and are strongly correlated to milkfat production.

Worth pursuing

With the rising cost of feed on dairy farms, homegrown forages provide an appealing option to reduce feed costs while potentially boosting component levels in the bulk tank. Because of this, high-forage diets have the potential to raise income over feed cost with proper management.