Farmers find many opportunities with grasses but don’t forget the benefits of alfalfa
Grasses have become more popular for inclusion in dairy diets, this has happened in many ways: grasses planted with the alfalfa in a mixture instead of pure alfalfa, pure stands of annual cool season grasses such as Italian ryegrass, and winter cereals such as triticale. There are multiple reasons for interest in grasses, but one is that they can have higher fiber digestibility than alfalfa has. Documentation of this trend can be found in the World Forage Superbowl results and in commercial lab averages when they report on different types of hay crops. In 2023, the World Forage Superbowl top 10 finalists for alfalfa haylage averaged 58.10 30 hour in vitro NDFD while the top 10 grass hay finalists averaged 67.07 by the same measure. A remarkable 9-point advantage for grasses achieved by growers growing the best of the best.
Interest in different crops comes and goes, and alfalfa has had a great run, is it now over for alfalfa? Alfalfa still has many great values. It is a perennial, protecting the soil over many years, it produces its own nitrogen, and it is high in protein and is deep rooted and somewhat drought resistant. Is the lower NDF digestibility the Achilles’ heel for alfalfa? The challenge is that dairy producers and nutritionists are interested in high forage diets for lactating cows, and as cows continue to increase in production the need for highly digestible fiber is greater than ever.
Laboratory average NDF digestibility values miss some aspects about alfalfa that need to be told. Just as corn silage is really a composite of two products- the grain and the fodder (stalk and leaves), alfalfa is a composite of two very different components: leaves and stems. The leaves have exceptional fiber quality, they are high in protein and the fiber is of excellent digestibility, it is the stem that is lower in fiber digestibility. When alfalfa matures and increases in lignin. The lignification and deterioration of fiber digestibility occurs primarily in the stem portion. Also, as alfalfa matures the stem to leaf ratio increases to the stem. Alfalfa becomes more proportionately stem, and the stem becomes increasingly less digestible and more lignified with plant maturity. Leaf diseases and harvest handling can also affect the portion of leaves as they can easily detach from the stem and be lost.
Not everything is undesirable about this stem portion, just as some rations become so digestible and have so little chew factor left to them that straw is added to the diet to keep the rumen working, the stiff alfalfa stem can be good for effective fiber and rumen health, just so it is kept in moderation.
Also, in defense of alfalfa in competition with grasses, the decline in fiber quality and the increase in total fiber is greater in grasses with advancing maturity than it is for alfalfa. In this sense the forage super bowl entrees, where everything went right, and harvest happened on time is not representative of what happens with all grass forages.
If we separate alfalfa into leaves and stem and do laboratory analysis on the two fractions separately, we will find the leaves are highly digestible and the high digestibility is also shown in the very shortest intervals for detecting fiber digestibility NDFD -12 hour for example. The early digestibility of alfalfa is greater for alfalfa than it is for most grasses, even if the total digestibility of the grasses is greater. Even though alfalfa is lower in digestibility than high quality grasses nearly all the alfalfa that will be digested has been made available prior to a 30-hour digestibility interval.
A meta-analysis by Johansen et al. (2018) showed that feeding legumes increased both DMI and milk yield compared with grasses. In vitro NDF digestibility may be a good indicator of filling effects for comparisons within forage families, grass or legume for example, however comparisons between widely different forages correlating NDFD to milk production are not perfect. Modern dairy cows with 60 pound or greater dry matter intake (DMI), will have had some portion of a grass forage leave the rumen before it has an opportunity to express its total digestibility, this levels the playing field between alfalfa and grass as the alfalfa will have delivered all it has to deliver more rapidly than the grass. High grass diets may have problems with rumen fill reducing DMI and may not have as much effective fiber as alfalfa.
Alfalfa has a unique fit in dairy rations- providing economical protein, being a much-needed perennial crop, and delivering a rapidly available highly digestible fiber fraction that is somewhat missed if you only look at the averages. Its fit with corn silage is also excellent, providing the quickly available fiber from the leaf fraction and more chew factor and rumen mat formation from the stem.
Think about the opportunities with grasses but don’t forget about alfalfa. We have a lot of history and understanding of how this crop feeds and it is an integral part of many high-producing herd’s rations.
Matt Lippert is the dairy educator for Wood and Clark County with the UW-Madison Division of Extension
