Dairy producers have recently expressed interest in feeding corn as shredlage. At the University of Wisconsin – Madison, Randy Shaver has been conducting feeding trials to see what makes it tick inside the cow.
He shared his results with those looking to put up feed for dairies at the Vita Plus Custom Harvester Meeting held this spring in Madison, Wisconsin.
Corn fed as silage contributes both starch and NDF to the dairy cow’s diet. The digestibility of the starch is based on kernel particle size, length of storage fermentation, kernel maturity and difference in endosperm properties.
Initially, corn silage was processed to reduce particle size of the kernels but not to achieve greater fiber digestibility.
“Particle size, or how well we process, is right up at the top of the list as to how well starch will digest in lactating dairy cows,” Shaver said.
This can be evaluated in terms of the kernel processing score. Samples of corn silage are dried and run through a series of sieves. Kernels remaining on the top screen will not be digested by the cow; the kernel processing score is the percentage that passes through the screen.
“I like to see 50 to 70 percent of starch passing through the coarse grid; 70 percent is optimal,” he said.
In a 2007 study, up to 10 percent of samples were optimally processed; the majority were in the adequate range and 20 to 40 percent had less than 50 percent pass through the top screen.
Samples from the Cumberland Valley Analytical Services in 2011 revealed 7 percent were optimally processed, 51 percent adequately processed and 42 percent inadequately processed.
“There’s room for improvement,” Shaver said. “Either with shredlage technology or just doing a better job of setting up the processor.”
As corn prices climb, producers want to take better advantage of the starch available in corn silage. An increase of 6 percentage units in starch digestibility is worth 2 pounds of milk, he said.
Corn can be chopped very fine and result in a silage with high starch digestibility, but it won’t provide any good to the cow in terms of roughage. Therefore, the chopped stover needs to have some length to it.
Chopping in the form of shredlage achieves longer length while at the same time getting good damage to the kernels. It is set for a 26 to 30 mm theoretical length of cut (TLOC) and 2 to 3 mm roll gap. In processing this way, the fiber material is flattened out or mashed.
Shaver asked: By tearing the fiber rather than crushing the kernels, is there some damage to fiber that increases fiber digestibility?
He performed a study in 2011 where conventionally processed corn silage (19 mm TLOC, 2 mm roll gap) and shredlage (30 mm TLOC, 2.5 mm roll gap) were harvested within one day of one another and stored in silage bags. Packing densities were at 17 to 18 pounds of dry matter per cubic foot between the two bags.
Nutrient composition of both forages were the same at 34 percent dry matter, 7.5 percent crude protein, 35 percent starch content and 35 percent NDF. They also fermented to similar profiles.
In a feeding trial six weeks after harvest, Shaver designed two experimental diets where everything in the diet remained the same, except one contained shredlage as 50 percent of dry matter while the other used conventional corn silage for 50 percent of dry matter.
Both diets had 17 percent crude protein, 25 percent starch and 28 percent NDF.
Each TMR was sampled in the bunk. The Penn State Shaker Box had 15.6 percent of material on the top screen of the separator box for shredlage vs. 3.5 percent for conventionally processed corn silage. Sorting was not found to be a problem with either diet.
The trial lasted eight weeks before all of the feed was used. The most noticeable effect was a difference in milk production.
While none of the cows produced poorly, having averages of 95 to 100 pounds, they did see a 4-pound advantage after six to eight weeks of feeding shredlage. Milk response for the entire eight weeks was up an average of 1.8 pounds on the shredlage diet.
Intakes were also higher at 1.4 pounds dry matter per cow on the shredlage diet. With 1.8 pounds more milk and 1.4 pounds more milk on the shredlage diet compared to the conventional diet, feed efficiency as calculated by milk per dry matter intake was about the same.
There was no significant difference in milk composition – fat, protein or MUN.
Shaver attributed the increase in milk to a 1.5 to 2 percent increase in total tract starch digestibility. “That’s 2 percent less starch escaping the cow through the manure,” he said.
There was a 4 percent increase in total tract NDF digestibility in favor of shredlage treatment. That doesn’t necessarily mean more digestible fiber, he said; the longer fibers could be improving pH in rumen or other factors that would increase digestibility.
To test this further, a rumen in situ study was performed where shredlage was placed into Dacron bags and suspended in the rumen.
The pore size of the bag allows bacteria to enter, but the particles within the bag don’t flow out. It is then incubated in the rumen for a period of time.
Using this method, starch digestibility for shredlage was 15 percent higher than the conventionally processed corn silage, but there was not a significant difference in terms of NDF digestibility.
This led Shaver to believe shredlage does not improve fiber digestibility of the forage, but it does improve the digestibility in the total rumen tract.
In another in situ study, the forages were dried and ground. In this instance, the shredlage did have greater NDF digestibility. This is an area for more research, he said.
Other questions also need to be answered, he said, such as: How do we achieve the greatest response potential?
For starch digestibility, it means looking at dry matter content, TLOC and fermentation time. If the silage is drier at harvest or going to be fed quickly, then it is important to achieve good kernel processing. Shredlage would also be something to consider for its longer chop length.
“If you only want to feed 15 to 20 pounds of wet corn silage and a lot of alfalfa, don’t worry about the longer cut,” Shaver said.
Response potential for physically effective NDF would come from using shredlage in low-forage rations or high-corn silage rations and as a replacement for chopped hay or straw.
A longer cut or shredlage approach might also have more application for BMR varieties, he said. Shaver plans to do a shredlage study this year looking at BMR harvested in that form.
In terms of digestible NDF potential, Shaver said somebody needs to sort out whether damaging the stover is helpful to NDF digestibility.
Whether someone chooses to harvest shredlage or conventionally processed corn silage, Shaver said processing control is important for both. TLOC and roll gap spacing need to be monitored to achieve an adequate or optimum processing score. PD
Karen Lee
Editor
Progressive Dairyman
