A consistent and abundant source of high-quality forage is key to successful implementation of high-forage diets. From time to time, forage shortages occur, which limits the feasibility of high-forage diets for lactating cows.
Dairy farms in many parts of the U.S. have been faced with a very unusual and very stressful forage growing season this past year. The challenges started early, with much of the corn crop planted very late due to wet field conditions, or in some cases, not planted at all. At the end of the season, many dairies ended up with corn silage with compromised nutritional quality and/or lower yields that resulted in insufficient inventories to last for the next 12 months.
If you anticipate a shortage of forages, first and foremost, you must have an accurate inventory of all the forages you have in storage on your farm. This is especially important for corn silage, since it is only harvested once per year. You must also calculate your overall forage needs, starting first with your lactating and dry cows, and know what your forage needs are for each month going forward.
Forage challenges have been threefold this year. The first has been forages with atypical nutrient content. Secondly, forage hygiene (molds, wild yeasts and mycotoxins) have been a problem. And lastly, insufficient quantities of high-quality forages available for lactating cows due to poor crop yields have presented challenges for many dairy farmers.
Forage quality issues
Due to late planting, some of the corn silage crop was harvested at an immature stage. Fear of frost impacting drydown prompted some farms to chop their corn prior to ideal maturity. Immature silage comes with its own set of challenges, including improper fermentation, excess moisture and low starch levels. All of these challenges can be assessed using standard laboratory analytics.
Immature corn silage can be a very useful feed for replacement heifers and far-off dry cows, but caution should be used when including it in lactation rations. After assessing the nutrient analysis of the forage, work with your nutritionist to make sure it will not adversely affect your milk cow ration.
Forages with excessive moisture are not only prone to improper fermentation, they also come with an increased risk of anti-quality factors, such as yeast and mold contamination. Molds and wild yeast can adversely affect the stability of the ration, and they can have a negative effect on animal health, feed palatability and performance. Warm weather usually accentuates these quality problems, especially those associated with wild yeast.
Bacterial silage inoculants and preservatives facilitate proper silage fermentation once the crop is in the silo and void of oxygen. However, inoculants are not a cure-all for poor-quality silage. Even if you treated your silage with an inoculant or other preservative, work with your nutrition advisor to closely evaluate the nutritional aspects of the silage, including forage hygiene, before using it in your lactation rations. Most forage analytical labs are able to quantitate the degree of mold and yeast contamination.
Forages in short supply
One of the more significant problems impacting dairies in some regions is a shortage of forages for milk cows. Given a choice, most dairies would choose to feed a ration that is 60%-70% forage to their lactating cows. However, due to reduced forage inventories, this will not be feasible for many dairy producers. If formulated correctly, rations containing 45%-55% forage can support good cow health and productivity.
When dealing with a forage supply issue, it is imperative to get a handle on your total forage inventory. This will give you and your nutritionist the information needed to allocate forages to make sure you have sufficient inventory to make it through until the next forage crop is available.
If “rescue” or alternative crops were planted, work closely with your nutritionist to see where they fit best into rations.
NDF sources
The fiber term most commonly used for balancing dairy diets is neutral detergent fiber (NDF). NDF consists of hemicellulose, cellulose and lignin. In addition to the chemical entity, forage NDF also provides some of the physical or structural fiber needed by the cow. NDF in the diet comes from two primary sources:
- Forages
- Byproducts (non-forage NDF)
Stretching forage inventories
There has been a continued interest in identifying alternative ingredients that can provide NDF and serve as partial replacements for forages. When you must reduce the forage content of your ration, you and your nutritionist must carefully select the ingredients that will serve as replacements. Byproduct feeds that are high in fiber (NDF) are the ones of most interest. They are referred to as non-forage NDF sources.
Non-forage NDF sources cannot replace all of the forage in a diet. Forage serves a vital function in the rumen, providing substance for the rumen mat, stimulating cud chewing, which in turn, increases the secretion of salivary buffers. Sufficient buffer is necessary for proper pH balance in the rumen, which impacts the end products of fermentation.
Non-forage NDF sources are often a good source of fermentable NDF; thus they are characteristically high in energy concentration. Due to the fact that they are digested more quickly than forage, they have a faster rate of passage. As compared to corn, non-forage fiber sources ferment more slowly and are less likely to result in rumen acidosis.
As far as chemical fiber (NDF) goes, many non-forage NDF sources have similar levels as forages. The primary difference between the NDF in non-forage NDF sources and forages is the particle size. Non-forage NDF particle size is smaller, thus it usually contributes little to the rumen mat.
Non-forage NDF sources include:
- Whole cottonseed
- Soyhulls
- Beet pulp
- Corn gluten feed
- Distillers grains
- Brewers grains
- Corn germ meal
Each of these non-forage NDF sources has some nutritional uniqueness, as compared to the forages they may replace in a ration. For example, whole cottonseed and distillers grains are relatively high in unsaturated fatty acids. These characteristics will limit the total quantity of the non-forage NDF that can be fed from whole cottonseed and distillers grains. The fatty acid profile of the entire diet must be considered to determine safe amounts to feed.
Local availability and price relative to other forage alternatives will dictate whether a specific non-forage NDF will make economic sense for a given situation.
How much forage NDF is needed?
Under normal conditions, a minimum of 21% forage NDF (NDF from forage sources) is desirable. In fact, many conventional diets have 25%-26% forage NDF. It will be a challenge to achieve these levels of forage NDF until next spring’s crops are available. Forage NDF levels in the range of 17%-18% may work when non-forage NDF sources are included in the ration and starch levels are kept under 24%. Whole cottonseed works very well in rations that contain low forage NDF levels.
How low you can go on forage NDF will also depend on the forage sources and forage particle size in the ration. Rations with haylage, balage or small-grain silages may be more suitable for lower forage NDF than rations that are predominantly corn silage. The Penn State particle size box can be used to assess forage particle size prior to implementing a ration that is low in forage NDF.
An example of a low-forage ration is depicted in Table 1.
Other considerations for successful application of low-forage diets:
- Hay or straw added to the diet should be coarsely chopped. Longer particle size will allow you to feed less NDF from forage.
- Limit rapidly-fermented grains. This includes any high-moisture grains, especially if finely ground.
- Provide sufficient “added” rumen buffer to manage rumen pH. This may include both sodium and potassium buffers.
- Low-forage diets are usually not recommended for cows in the first 30 days of lactation, because of limited dry matter intake. If you have a fresh cow group, use discretion in how much you reduce the forage for this group.
- Avoid significantly overstocked cow pens. Low-forage rations result in less chewing, hence cows can consume feed more quickly. Overcrowding increases competition, which encourages slug feeding and can lead to sub-clinical acidosis.
Low-forage feeding programs can be successful if used in conjunction with non-forage NDF sources. However, these programs must be managed carefully. Cows fed low-forage diets are at a greater risk of developing subclinical acidosis, low milk fat, sore feet and reduced feed efficiency; therefore, ration ingredients must be selected carefully and cows must be monitored closely. 
Don Jaquette is a dairy nutritionist with ADM Animal Nutrition. Email Don Jaquette.
