The Penn State Particle Separator (PSPS) provides a tool to quantitatively determine the particle size of forages and total mixed rations (TMR). The updated 2013 version of the PSPS adds the ability to estimate physically effective fiber (peNDF) to this tool. The concept of measuring feed particle size using a standard method is not new.
The American Society of Agricultural and Biological Engineers’ (ASABE) standard for particle size analysis and distribution has been available for many years. Unfortunately, the ASABE method is a cumbersome laboratory procedure that is impractical for farm use. The objective of developing the PSPS was to mimic the complex lab method with a simpler, on-farm method. The newest refinement allows for an estimation of the quantity (%) of a forage or TMR that provides physically effective fiber to the dairy cow.
The goal of analyzing TMR particle size is measuring the distribution of feed and forage particles the cow actually consumes. The focus is not only on particles greater than a particular size, but also on the overall distribution of feed particles consumed by the cow. Measuring TMR samples fresh from the feed bunk before the cows eat or sort the feed is recommended. Mixing and distribution equipment can reduce particle size of feeds and forages and need to be accounted for by evaluating the actual diet being fed.
Physically Effective Fiber or peNDF
Measurement of peNDF has become widely used in dairy cattle nutrition and research. The original system of peNDF was developed by Dr. Dave Mertens of the US Dairy Forage Research Center. It measured fiber particle size using dry samples of feed in a 3-dimensional, vibrating sieve system (Ro-Tap separator; measuring smallest particle dimension) and had neutral detergent fiber (NDF) on the whole sample. Most forage is now measured in a 2-dimensional sieve device (such as the PSPS; measuring particle length). Using peNDF in ration balancing and troubleshooting, along with a single NDF value, may prove to be a useful tool in troubleshooting rations and cow performance.
The original peNDF procedure used 1.18 mm as the critical size at which feed particles are considered physically effective for dairy cows. This number originated from earlier research that determined 1.18 mm was a threshold particle size determined with both cattle and sheep (at maintenance intakes) for greatly increased resistance to particles leaving the rumen and that less than 5% of fecal particles were generally retained on a 1.18-mm sieve.