One of the biggest advancements in feed analysis from our forage testing labs has been the addition of uNDF240 as a measure of indigestibility. While NDFD30 is an estimate of the amount of fiber digested in 30 hours of contact with rumen fluid, uNDF240 is the amount that is undigested in 240 hrs. The concept is that after 10 days in rumen fluid the remaining fiber will not digest further. This number has allowed us to more accurately predict whether a high-forage diet is even possible, and then, just how far we can go without losing Energy Corrected Milk (ECM
In the distant past, we used ADF or NDF as the limit for dry matter intake (DM) and our results were mixed, at best. Lignin was then used to help us determine forage feeding limits. It was sure better than nothing and way better than NDF, but there were still several problems with its usage. First, lignin is a small number, and many times, not able to be accurately measured. Tables 1 & 2 show alfalfa and corn silage samples with approximately the same NDF and lignin, but with much different NDFD30s.
As can be seen in these tables, the agreement between NDFD and lignin is very low. So not only do we have low agreement with lignin to digestibility, but we also have a number, lignin, the labs say is not very accurate to start with. Garbage in garbage out or GIGO!
The point is lignin is not the extent of the indigestibility. Biological processes such as cross-linking of the undigestible lignin to the very digestible hemicellulose renders the hemicellulose less digestible, also. The solution was to multiply the lignin percent by 2.4 (an educated guess by people much smarter than me) to account for the true indigestibility. Of course, multiplying an inaccurate number by another inaccurate one does not lend credence or accuracy in diet formulation. It was possibly more correct than an alarm clock with a dead battery!
One other problem with the 2.4 number is that it was used across all forages. Guess what? All forages are not the same! Not only are maturation rates different, but the cross-linking operates differently in an alfalfa compared to grass or corn silage.
Thus, uNDF240 accounts for the cross-linking in all forages, and has allowed us to more accurately predict whether a high-forage diet is even possible, and then, just how far we can go without losing Energy Corrected Milk (ECM). Whether or not you are using this number from the feed analysis report, it still must be dealt with! What has been discovered is, there is a limit of how much uNDF240 a cow can eat, and unlike lignin, it is a consistent and accurate number.
What we have when we subtract the uNDF240 from 100% is the potentially digestible NDF or pdNDF. However, we use the uNDF240 to determine if, when a diet is proposed, it can be a successful high forage diet.
Yes, we can use low lignin alfalfa and BMR corn silage, but all we get is a contest to see how much our cows can eat! The goal is not to get cows to eat as much as possible, it is for them to get the most out of each pound of feed they eat. Higher intakes can be a result of faster rate of passage through the cow’s digestive system–much of it unutilized. So, while feeding a ration that is very high in potentially digestible fiber, much of it goes undigested. It makes for expensive manure.
So, what good does knowing the uNDF240 level of all our forages on a dairy? It is (so far) the most accurate number for determining DMI and also how much forage can be fed while maintaining high performance. When using non-traditional forages, uNDF240 gives the confidence to use the Innovation Diet metrics.
How did we get away without it in the past? At least in the Upper Midwest, most diets were the same – a high percentage of BMR corn silage and a low percentage of alfalfa. When diets are identical, it is easier to predict. Will this drive high DMIs? You bet! Will it be the most profitable diet? Unlikely! You will be producing a lot of valuable manure along with your milk check. It is just hard to pay for the extra feed for extremely high DMIs with manure. Put more of your forage toward producing ECM!
So, what is the Innovation Diet? A high-forage diet which does not push the forage out before it is digested. What forages are used in the Innovation Diet? Corn silage plus cool and warm season grasses, clovers plus small grains. These forages produce more tons of feed per year, more tons of digestible fiber by a long shot, and provide both year-around forage cover crops and always a place to go with manure.
To be sure, we are not saying to do anything to reduce dry matter intake (DMI) on the management side. We are just saying to feed forages that move through the cow just a little bit slower, so you utilize all NDFD30 you paid for. Get more milk out of each pound of feed, not more feed into the cow.
What can this mean to feed less feed and still get the same amount of ECM? Just figure what a pound of your diet costs, and what it will mean if you are able to feed between 5 and 10% less feed from your current DMI. It will be thousands of dollars and hundreds of thousands on large herds! You are not in the business to produce more manure and surely not to buy or raise more feed to support inefficient diets.