Forage particle size recommendations that boost cow comfort

Posted on August 22, 2023 in Forage Foundations
By Rick Grant, William H. Miner Agricultural Research Institute

Forage quality is an overlooked component of cow comfort.  Forage particle size, NDF degradability, fragility and dietary forage percentage must allow the cow to consume feed within 3 to 5 hours per day.  Too much forage fiber, poorly digested and/or coarsely chopped forage will extend eating time beyond 5 hours per day and probably limit dry matter intake (DMI).

Kurt Cotanch, a former forage lab director at Miner Institute, and I published a perspectives paper on this topic in the June issue of Applied Animal Science (39:146-155).  The figure and table in this article are adapted from this issue.  Research shows that the primary role of forage particle size in many feeding scenarios is on eating rather than ruminating activity because cows typically chew to a fairly constant endpoint before swallowing.  Consequently, the rumen is populated with a forage particle distribution more uniform than common corn silage and haycrop silage-based TMR.

A balance must be struck between eating and recumbent (i.e., lying down) rumination time.  Recommended TMR particle distributions for the Penn State Particle Separator (PSPS) that optimize the balance between eating and ruminating is summarized in the table.  Only 2% to 5% of particles should be retained on the top sieve, and the particles shouldn’t exceed 1 to 2 inches in length to minimize sorting.

At least 50% of the ration particles should be retained on the 8-mm sieve of the PSPS.  These particles do not promote excessive eating time or sorting, and they effectively stimulate rumination.  Particles retained on the 8-mm sieve are similar in size to the swallowed bolus of feed during eating.  A TMR containing 50% to 60% of these particles is easily eaten by the cow within the recommended 3 to 5 hours per day.

Sufficient access to stalls and resting areas encourage recumbent rumination.  A well-formulated, accessible TMR with appropriate particle size needs to be paired with comfortable stalls or other resting resource so that once cows are done eating, they can easily lie down and ruminate.  Recent research shows that greater recumbent rumination results in healthier rumen pH, greater DMI, and milk with more fat and protein content.

Adjusting theoretical length of cut based on forage-fiber degradability, fragility and moisture content (adapted from Grant and Cotanch, 2023).

The figure depicts an approach to adjusting length of cut to properly balance eating and rumination activity.  Two years ago, Bill Woodley of Woodley Dairy Direction in Ontario, Canada, first proposed this approach.  For example, mature forage with greater undegradable fiber benefits from shorter chop length to maintain intake.  The balance between eating time and recumbent rumination should be responsive to this range of theoretical chop lengths.  In the future, this concept can be refined with more research, but for now, use it in the field as a starting point for adjusting forage particle size.

Sieve size, mm % particles retained, as fed Importance of particles retained on the sieve
19 2 to 5 Potentially sortable material, increases time needed for eating, especially if >10%
8 >50 Physically effective; target 50% to 60% retained on this sieve
4 10 to 20 Functions as physical effectiveness factor (pref) sieve; total on the top 3 sieves = pef
Pan 25 to 30 40% to 50% gran diet results in at least 25% to 30% in the pan


Category: Animal health
Feed quality and nutrition
Forage Foundations
Forage harvesting
Forage storage and management