Dr. John Goeser, PAS & Dipl. ACAN
Rock River Laboratory, Inc. nutrition and technical support
New corn silage, snaplage/earlage, high moisture corn and dry corn grain are nearly wrapped up. Year after year we experience different performance, in some cases a slump, when we begin feeding new corn feed crops. Yet the performance response is variable and we have historically not understood why new crops feed differently.
Ten years ago, during graduate school, I began to understand why performance lags when feeding new crop corn thanks to teachings by and coaching from Prof. James Coors, Prof. Randy Shaver, Prof. Pat Hoffman and others with the Univ. of Wisconsin – Madison. In 2014, I had the pleasure of fully investigating the “new crop slump” and presenting findings to consultants attending the California Animal Nutrition Conference. The bottom line? New crop slump is largely due to rumen and total-tract starch digestion differences (Goeser, 2014 CANC).
We better understand this dairy and beef feed facet but we’re still challenged in forecasting the performance response. Will milk production decrease by 1 or 5 lbs. per cow? Will average daily gains drop 5 or 15%? Will performance even change at all? Any change in performance can and will eventually be corrected by your consulting team, without a doubt. However opportunity costs following delayed corrective action cost money. Will the corrective nutrition program be put in place in 7 days? Or will several iterations need to be tested, potentially taking a month or more as we let the cows tell us where we need to be? Every added day, with even 1 lb. per cow performance opportunity, costs $20 for every 100 head on feed. The aim is to figure corn and corn silage feeds out, faster. So how do we assess starch digestibility potential?
Forage testing laboratories have adapted and developed rumen simulating digestion techniques from published literature. There are three general levels that one can assess starch digestion potential, generally summarized as follows (adapted from Goeser, 2014):
We need to keep in mind that the gold standards are in vivo measures, and any other approach to determine nutrient digestion should be compared, on some level, to in vivo to demonstrate validity. While many different in vitro techniques exist, at least a few have been validated. For example, two different in vitro approaches have been compared and validated against in vivo measures; rumen in vitro NDFD (Lopes et al., 2015) and intestinal in vitro CP digestion (Boucher et al., 2009). The same can not be said for starch digestion approaches.
In the absence of a validated approach, the another option to assess validity is to compare in vitro or in situ digestion data to that published in the literature for in vivo measures. While anecdotal, and not to be confused with true validation, we took this approach to gauge in vitro and in situ rumen digestion approaches for starch (Heuer, 2014; Goeser, 2014)
When comparing against published literature (TMR rumen in vivo starch digestion averaged 59%; Goeser, 2014) we find that in situ rumen starch digestion results for a variety of feeds, using a larger sample and greater particle size, yield similar average and range as published TMR in vivo starch digestion measures.
The in vitro digestion technique seemed to yield excessively high starch digestion values and also smaller range (69% in vitro rumen starch digestion for a variety of feeds; Heuer et al., 2013).
To be clear – neither of these starch digestion techniques have been directly compared to in vivo results under a controlled experiment. However, the rumen in situ digestion approach seemed to yield similar mean and range as the in vivo published data, hence Rock River Laboratory has proceeded with an in situ rumen starch digestion approach. This technique has also served as the basis for routine NIR forage analysis calibration development, yielding a repeatable calibration for day to day use.
In summary, the rumen in situ starch digestion assay can be used to better forecast starch digestion potential and help consultants more quickly alleviate, or possibly prevent, performance slumps due to starch digestion. Having added knowledge about the crops’ potential will help us continue to improve precision and performance.
Here are rumen in situ starch digestion benchmarks:
7h, % of StarchGoal>75Average60-70Low40
High Moisture Corn grain
Boucher, S.E., S. Calsamiglia, C.M. Parsons, M.D. Stern, M. Ruiz Moreno, M. Vazquez Anon and C.G.Schwab. 2009. In vitro digestibility of individual amino acids in rumen-undegraded protein: The modified three-step procedure and the immobilized digestive enzyme assay. J Dairy Sci 92:3939-3950.
Goeser, J.P. 2014. Comparing new crop to old crop – what might cause the new crop slump? Proc. California Animal Nutrition Conference, Fresno, CA.
Goeser, J.P. 2014. What do the cows have to say about NDF and starch digestion. Proc. 4-State Dairy Nutrition and Management Conf., Dubuque, IA.
Heuer, C.M., J.P. Goeser, and R.D. Shaver. 2013. Starch digeson variaon between in vitro and in situ digeson techniques. J. Dairy Sci. Vol. 96, E-Suppl. 1, Pg. 29
Heuer, C.R. 2014. Masters of Science Thesis. Univ. of Wisconsin – Madison.