Adapted by Jennifer Heguy, UC Dairy Advisor - Merced, Stanislaus & San Joaquin
Summer forage harvest is upon us, and so is a flurry of silage choppers, trucks and packing tractors. Putting feed up quickly is imperative to the ensiling process, making monitoring during harvest equally important. A dairy can harvest and ensile a year’s worth of forage in as little as a few days; if the desired chop length is not met, or kernel processing is not adequate, there could be issues with how the forage performs in the ration.
Chop length of forages can be measured as it’s delivered to the silage structure. In a recent corn silage management survey, 80% of dairies reported monitoring chop length during harvest with 97% of those dairies doing so visually. Another, less popular but more precise method of evaluating chop length on farm is the Penn State Particle Separator (PSPS) analysis.
What is a PSPS?
In figure 1 (figures and tables are on page 2), there are four numbered piles which correspond to the trays of the PSPS (figure 2). The top 3 trays have openings for material to pass through (Table 1), becoming gradually smaller with a solid bottom tray to catch the “fine” material. For reference, recommended ranges for corn silage and haylage are also included in table 1.
How do I use a PSPS box?
A sample of harvested forage is placed in the top tray of the PSPS (with the other trays stacked under) and “shaken” and rotated according to the instructions. Then, material in each of the trays is weighed and calculated as a percentage of the total weight. The entire process can be completed on farm, in about 5 minutes. For more information: http://extension.psu.edu/animals/dairy/nutrition/forages/forage-quality-physical/separator
PSPS results from harvested sorghum
Last summer, 16 fields of sorghum chopped for silage (nutrient and management information was presented in the April 2017 newsletter) were sampled. There isn’t a lot of information available on desired sorghum chop length, but the results were still interesting. Table 2 includes the average, median, minimum and maximum percentages of the 16 chopped sorghum samples at harvest. Compared to corn silage, these sorghum samples were chopped much coarser than typical corn silage and evidenced by the large percentage of material found in tray 1. Tray 3 contained less material than typical corn silages, which may be due, in part, to the lack of starch (sorghum grain) as compared to corn silage. Individual results from the PSPS analysis (including pictures) can be found here: http://ucanr.edu/casorghum16.
Full color articles and photos are available on our Website: ceglenn@ucanr.edu
Figure 1: PSPS tray forage fractions
Figure 2: PSPS showing trays
Table 1. Forage separator characteristics (2002 model) and recommendations for corn silage and haylage.
From Penn State Extension: http://extension.psu.edu/animals/dairy/nutrition/forages/forage-quality-physical/separator
| Pore Size (in) | Particle Size (in) | Corn Silage | Haylage |
Tray 1 | 0.75 | >0.75 | 3% to 8% | 10% to 20% |
Tray 2 | 0.31 | 0.31 to 0.75 | 45% to 65% | 45% to 75% |
Tray 3 | 0.05 | 0.07 to 0.31 | 30% to 40% | 20% to 30% |
Tray 4 | solid bottom | <0.07 | <5% | <5% |
Table 2. PSPS results of chopped sorghum (n=16) taken at harvest
| Average | Median | Minimum | Maximum |
Tray 1 | 28% | 27% | 3% | 59% |
Tray 2 | 51% | 52% | 17% | 70% |
Tray 3 | 20% | 21% | 7% | 29% |
Tray 4 | 2% | 2% | 0.3% | 4% |
Take home thought
Desired chop length can vary, depending on several factors, including end user (heifers vs. lactating cows) and presence/absence of other forages in the ration that can provide long particles. When particles are too long, sorting may become an issue; too short and rumen issues may occur. Talk with your nutritionist to determine the desired chop length of your summer forages, and monitor chop length throughout harvest to ensure your end product meets your dairy’s needs.
Link to PDF Version: Monitoring Forage Particle Length- How and Why