Based on a presentation at the 2018 Silage for Beef Cattle Conference at the Eastern Nebraska Research and Extension Center.
The energy value of whole-plant corn silage (WPCS) contributed by starch is approximately 50%. An increase in starch digestion may lead to better nutrient utilization and decreased feed costs. However, starch digestibility of WPCS may be affected by several factors.
Factor 1: Kernel processing and length of cut
Corn is a seed and has a hard coat, the pericarp. The breakdown of the pericarp and exposure of the starch (endosperm) must be the primary objective at harvest to maximize energy availability.
Kernel processors enhance kernel breakdown at harvest. This is related to increased surface area for bacterial and enzymatic digestion of finer particles. Degree of kernel processing may be inhibited by other factors, such as the length of cut. Processing increased the diet total tract starch digestibility (TTSD) when the theoretical length of cut (TLOC) was set at 0.37" to 1.13" but not when length of cut was shorter or longer. This is likely related to greater kernel breakage by cutting knives when using short TLOC settings.
Other factors – such as proper processor maintenance from wear, frequent quality-control monitoring of kernel breakage during harvest, and adequate TLOC and roll-gap settings for the chopper and processor used – are also crucial for obtaining optimal kernel processing.
Factor 2: Maturity at harvest
Delayed harvest may increase concentration of starch while proportionally reducing concentrations of CP, NDF and ash.
On the other hand, maturity at harvest may also negatively influence the breakdown of kernels. Kernels in very dry – and mature – WPCS tend to be less susceptible to breakage during kernel processing at harvest. Increased maturity at harvest may limit not only starch, but also NDF digestibility of WPCS.
Factor 3: Chop height
Chop height can help reduce lignin concentration. Lignin is an important component concentrated in the bottom part of corn plants. With a higher chop height, more lignin is left with the portion that remains in the field, and, thus, the overall quality of the harvested material is greater.
Results from a recent industry-university collaborative study compared 6" to 24". These results are similar to other trials comparing 6" to 18" of chop height. The results show that DM yield is reduced as the row-crop head is raised. This is consistent across several studies conducted across the United States.
Determine individual farm priorities for maximum yield versus higher quality, prior to the establishment of new chop height guidelines.
Factor 4: Silage fermentation
Extended WPCS storage length can result in a gradual increase in starch digestibility as fermentation progresses. Studies show that – at 30 or 45 days of ensiling – ruminal in vitro starch digestibility (ivSD) was increased by 7 percentage units. These studies also showed a gradual increase in ivSD after 30 or 45 days of additional storage (approximately 60 to 90 days of fermentation).
Although allowing an extended ensiling period may be beneficial for increasing starch digestibility, research does not support the same fate for neutral detergent fiber (NDF) digestibility.
To download proceedings of the 2018 Silage for Beef Cattle Conference, or watch a video of the presentation, visit . The conference was sponsored by Lallemand Animal Nutrition, the University of Nebraska Extension and the Iowa Beef Center.