The digestibility of the starch component of corn silage is influenced primarily by kernel processing and ensiling time. Starch digestibility in corn silage is important because about half of its energy value comes from the starch which is provided by the grain fraction. We presented results from a sample survey of commercial testing labs over 2005 to 2012 showing a high percentage of corn silage samples categorized with poor processing (up to 42%) and a low percentage of samples categorized with excellent processing (only 7% to 17%) based on processing score measurements.
Since then, different corn silage processing has been implemented on some of the self-propelled forage harvesters being used on farms. The changes include shredlage processors, shredder rolls, conventional processors with greater roll speed differential, and inter-meshing disc processors. Additionally, there has been a lot of recent interest, especially with the feeding of higher corn silage diets, about setting the forage harvester for a longer theoretical length of cut (TLOC) with the aim of increasing the particle length of corn silage. Further augmenting this interest is the recommendation for longer TLOC when using shredlage processors.
The objectives of this field trial were to survey dairy farms about their corn silage harvest, processing and feeding practices, and collect corn silage samples during silo feed-out for determination of processing score and particle length.
Seventy-six corn silage samples were obtained from 69 dairy farms during farm visits April to August 2014. The samples were collected from the pile that had been shaved from the exposed face for feeding.
Dry matter (DM) content was determined on corn silage samples by drying at 60°C for 48 h in a forced-air oven. Dried samples were used for determination of starch content by NIRS. As-fed samples were used to determine particle size distribution using the Penn State manual shaker box (PSU-SB) with 3 sieves and a pan. Also, as-fed samples were sieved mechanically using the Wisconsin Oscillating Particle Separator (WI-OS) to determine mean particle length (MPL). Corn silage processing score (CSPS) was determined on dried samples. During each farm visit a survey questionnaire was completed to assess herd demographics, corn silage harvesting practices, feeding practices, and farmer perceptions with regard to animal- and equipment-related responses.
Results and discussion
Most farms (61%) harvested corn silage using a Claas SPFH equipped with a Shredlage® processor. Bunkers (95%) and inoculants (87%) were used by most farms. Corn hybrids were solely dual-purpose type for 43% of the farms. Most farmers reported a 22-26 mm TLOC (79%) and a 1.5-2.5 mm roll gap (82%). There was no attempt to verify the reported settings on the equipment. It should be noted that these data are a single snap-shot in time and may or may not be reflective of the corn silage fed on these farms in the months before or the months after our survey was performed.
The content of DM and starch was similar for the shredlage- and all-sample sets. While the average content of DM and starch was indicative of high-quality Midwest-USA corn silage, the range among farms was wide for both; DM range, 25.6%-47.1%, and starch range, 17.1%-42.6%. This likely reflects the challenges of weather conditions and harvest scheduling. Reducing variation in DM content is an area where corn silage quality could be improved.
Although the percentage retained on the top or coarsest PSU-SB sieve was 7%-units greater for shredlage than the other categories on average, the percentage retained on top 2 PSU-SB sieves and the WI-OS MPL were similar. This suggests that there may not have been much improvement in physically-effective fiber for the shredlage samples compared to the other samples collected in this survey. The average percentage retained on the top PSU-SB sieve for shredlage was substantially lower than previously reported in a 2012b feeding trial (20% versus 32%). It should be noted that the TLOC setting on the SPFH was 30 mm in the previous study, while the TLOC was usually 22-26 mm for the shredlage samples in this survey. The ranges for shredlage samples were: PSU-SB top sieve was 7.2%-39.9%, PSU-SB top 2 sieves was 65.1%-85.9%, and WI-OS MPL range was 9.0%-14.8%.
All sample types fell in the adequately-processed category based on CSPS. The CSPS was only 2%-units greater for shredlage than the other sample categories on average. This was achieved, however, coincident with the greatest percentage fibrous-particle retention on the top sieve of the PSU-SB for shredlage. The range for CSPS in shredlage was 33%-units, and both the greatest and lowest CSPS were observed within the shredlage samples.
On-farm feeding experience with these new-types of corn silages was limited with only 20% of respondents using for over 12 months. Only 22% of respondents had increased total forage content of their diets, while 47% increased the corn silage content of their diets which indicates a greater proportion of corn silage in the total forage DM. With regard to the inclusion of hay or straw in the TMR, 54% of respondents still did so and only 40% of those had reduced the amount fed.
Farmers were also asked animal-related survey questions. Increased or no change were the most common responses to all questions, and these were relatively evenly split for milk yield and fat content. Nearly two-thirds of the respondents reported no change in feed sorting, while only about one-third of respondents reported improvements in herd health and manure scores.
Processing rolls were relatively new with only 23% of respondents reporting usage on more than 30,000 as-fed tons. Only about 5% of respondents felt that silage packing density had decreased. Most respondents reported either no change or being unsure about tons per hour (57%), fuel usage (64%), and roll wear (76%).
The physical form (PSU-SB, MPL, and CSPS) and DM results indicate considerable opportunity to improve corn silage quality by reducing variation through better process control during harvest for shredlage and non-shredlage type samples. It appears that major changes in feeding programs were not made coincident with the use of new-type corn silages. Because this survey was a single snap-shot in time and most farmers still had very limited experience harvesting and feeding new-type corn silage, a follow-up survey is warranted.
Author: Randy Shaver, Department of Dairy Science, University of Wisconsin–Madison
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