I suggest we use this post to share actual data we collect from farms relative to high chop corn silage. The simplest metric to look at is the RFC-Fill index that I developed a few years ago. It is (NDFd30 + starch)/NDFu30. Dr. Kemp shared information from a small trial he did on a client.
They chopped a field of BMR with the chopper set at three different heights – 12″, 16″, 20″. The BMR was wet (29% DM), low starch (28% Starch) and high NDFD (69%).
Height RFC-fill index
12″ 4.39
16″ 4.26
20″ 4.27
I suspect there is no statistical difference in these samples (you would not build a different diet accordingly) and there is a lot of dry matter left in the field. As Dr Kemp suggested (“If we grow it, we should harvest it”).
I was on a herd yesterday that Rachel Brong feeds. They are high chopping corn silage for a variety of good management reasons (Rachel, can you outline these for discussion). We chopped alternating loads as high and normal cut (4 total). These we sampled and sent to the lab yesterday afternoon. We should have the results back Thursday or Friday and will share them here.
If anyone else has mini-trials can you share the data here?
Thanks,
Larry
I have some interesting data from a herd that Rachel Brong works with. Rachel, feel free to add additional comments.
This was a field demonstration where alternating truck loads were chopper either high or low.
Raising the chopping from 6″ to 18 inches increased the starch from 33% to 42%, lowered the NDF from 42% to 33% and raised the NDFD from 59% to 61%. The resulting RFC-fill index increased from 3.35 to 4.64. With a final NDFu30 value of 13% of DM and starch over 40% makes this feed like a high starch BMR.
Using a model that I prepared for GrowmarkFS, this suggests that there is $0.37/cow/day increase in value. This particular herd decided to chop high for a number of practical reasons and they were not concerned about the addition cost. The main cost is in yield drag where the same dollars per acre are spread across fewer tons. Using a lot of assumptions, I created a 9% yield reduction starting with 20 tons/acre at 35% DM. This results in an increase cost of $0.40/cow/day. The net result is basically break even. For complete disclosure, I used 0.10/lb for both starch and NDFd30. We plan to repeat this collection near the end of harvest. If you perform this test and have data you want me to analyze for you, send the CSV files to info@theCWTgroup.com
A couple of questions: 1) would you really have a 9% yield reduction by leaving 12″ of lower stalk in the field? For easy math assume plant is 10′ ft, this would leave 10% of the height but much less than 10% of the weight given leaves, tassel and ear. 2) Do the math – NDF decreased from 42% to 33% with minus 9% of weight left in field, the NDF of that left is >100%? I know 9% is an estimate but non-the less the value of the 12″ of stubble difference has to be worth much less per ton than the remainder that was harvested.
I realize 10′ plant is stretching it for a 20 ton yield.
I sent out more samples today of high vs low in a different field. Will report when I see the results.
OK, here is the math I did. Assume the plant is 10′ tall and the ear is at 4′ from the ground. I have measured a bunch lately and that seems about right. I assumed 50% of the dry matter was in the ear and 50% in the stalk. Then I assumed 70% of the stalk is below the ear and 30% above. If I left 25% of the 70% of the 50% that should equal about 9%. I have to say that I estimated the 20 tons/acre for easy math. The yield drag was 9% or 1.8 tons/acre.
A lot of estimates but the literature showed a 7.5% yield drag so Joanne and I thought it was close. I come up with the remaining plant being 58% NDF.
Low chop High Chop Residual
Percent harvested 100 91 9
NDF 33% 42% 58%
Pool 33 38.22 5.22