From time-to-time, questions come up which inspire a newsletter article. The question from this title has been around longer than feed testing! (Feed-testing labs began to come on the scene in the 70s and yes, I was there!). This is just to say this problem is an age-old occurrence.
Obviously, there are many reasons milk production on a modern dairy can go down but let us assume all the other problems have been eliminated. We have audited the mixing, cleanliness (lack of molds, yeast, etc.) feed bunk space and adequate time budgets for cows to eat, drink, ruminate and be milked, and the whole myriad of things which can go wrong. So, what are the “forage” things we look at when feeding high-forage diets?
So, Where is the Culprit?
Especially when we are feeding at least some unconventional forage for modern high- producing dairy cows, whenever things do not go as expected, the first point of blame is almost always the alternative or the unconventional forage. It is, of course, a place to look, but we feel there is a more basic and determinative place to look when the goal is providing a high-forage diet capable of producing lots of milk.
A basic principle is that energy takes up by far the most room in any diet. Nutritionists and producers have for a long time now realized that the digestibility (NDFD30) of a forage (not the protein!) is the first thing to look for on a feed sample report. If this number is not adequate, it becomes impossible to develop a high-forage diet with this particular forage as a major ingredient.
NDF in my early days in the dairy nutrition business was thought as being monolithic across all types of forage. For example, the NDF of vegetative grass was the same as the NDF of alfalfa. Eventually, we came to discover they were extremely different. As the evolution proceeds in the understanding NDF, we can now more clearly understand when we have the types of forages needed to implement a high-forage diet, or additionally, how high the forage can go.
Moreover, digestibility is only one side of the equation especially when a high-forage diet is the goal. The indigestibility also becomes important. In the history of ration formulation various aspects of the ration fiber indigestibility were utilized to determine the availability of the forage’s energy and the contribution that forage made to the cow’s dry matter intake (DMI).
ADF in the 70s was the first determinant. Then lignin started showing up on feed sample test reports in the mid-90s. Lignin as the determinant for dry matter intake (DMI) and digestibility were found wanting as we needed to start accounting for the cross-linking of the hemicellulose and the lignin (both along with cellulose are the main components of NDF). The three elements of NDF exist in different proportions within the NDF in our various forages and therefore alter the digestibility.
The next attempt was Lignin times 2.4. This was an educated guess as to how much cross-linking occurred, but still treated all forage alike.
All these estimations of indigestibility were based on the presumption NDF was monolithic. However, the NDF is not the same in corn silage, alfalfa, small grains, and cool or warm season grasses. The relative percentage makeup of the three main elements of NDF (i.e., Lignin, Cellulose, and Hemicellulose) are different for each forage type and for individual forages within each of these groups. Factors include species, maturity, variety, and of course, weather. Because of the high concentration of hemicellulose in vegetative grasses, grass NDF is the most digestible.
Hemicellulose, really a 5-carbon sugar is extremely digestible until some form of cross-linking with the lignin occurs. Cross-linking of the lignin to the hemicellulose renders the total NDF to be less digestible. To measure the effect of the various cross-linking processes in our forages, a new metric was developed termed undigested neutral detergent fiber in 240 hours or uNDF240. It can be reported as either a percent of the dry matter or of the NDF, just as lignin is. When two forages of vastly different NDF240s such as sorghum sudan and alfalfa or corn silage, the comparison to the uNDF as a percent of NDF gives a much clearer and fairer picture.
The NDF content of cool and warm season grasses, small grains and corn silage can be so different. For example, BMR Gene 6 sorghum-sudan silage has an extremely high NDF, high sugar, but almost no starch. At first glance, it appears to have far more uNDF240 than high-starch corn silage as a percent of DM but is a different picture when comparing to the percent of the NDF.
This number uNDF is a proxy to determine the endpoint of digestion or what would remain undigested at the end of an infinite time. Most of us do not have that long to wait so the 10-day or 240-hour time point is used to know how much fiber will never be digested. Most of us do not even have 10 days to wait, but NIR testing provides our needed answer in mere minutes after the sample arrives at the lab!
Finally to the Original Question
So, to finally get to my point of this article! Many times, the problem of forage quality from year or crop to the next can be seen in the uNDF240. uNDF240 is the strict limiter of dry matter intake. When we reach the limit of total pounds of uNDF240 a cow can eat, all further attempts to improve pounds of milk per day production ends! At that point forages with a lesser contribution of uNDF240 are needed. And the forage needed to cure is almost never alfalfa!.
So, What are the Numbers
Obviously, breed, body weight and to a lesser extent, particle size play a big role as to how much uNDF240 a cow can eat. Also, there are both maximums and minimums for uNDF240 and we can think of it in the same way as we did with lignin. A minimum amount of uNDF240 is needed as to aid rumination. However as stated above, uNDF240 is the strict limiter of DMI with only some help by finer particle sizes. We would be glad to discuss our empirical findings with any nutritionist who would like a discussion. uNDF240 is something you deal with whether you look at the numbers or not!
The Bottom Line
Of the biggest benefits of the Rethinking Rotations and the Innovation Diet program is the ability to truly increase Milk Efficiency as measured by energy corrected milk (ECM) divided by the actually pounds of feed eaten. With the forages we utilize with high yields, high digestibility and low uNDF240, we can feed a high percent of forage diet. At the same time and this seems antithetical to many, with the proper ratios of small grains, red clovers and cool and warm season grasses plus corn silage, the cows eat slightly less when compared to BMR corn silage and low lignin alfalfa diets.
The premise to promote the common diets and the huge DMIs resulting from feeding Low Lignin alfalfa and BMR corn silage is that cow maintenance is spread across more pounds of feed and thereby become more efficient. What actually happens is feed is moving out of the rumen so fast, we do not get all of our promised NDFD. Efficiency is lost! When we can reduce this rapid outflow of feed slightly (5 to 10%), and still provide the needed energy, we are getting more milk from each pound of feed. Not more feed into each cow! This gain can be $150,000 to $300,000 for each 300 cows in your herd per year!