When we think about forage particle size, the conversation typically centers on effective fiber, rumen fill and milk components. Dr. Rick Grant, president of the Miner Institute, believes the industry may be asking the wrong question.
Rather than focusing solely on whether a ration stimulates enough chewing, Grant argues that we should consider how forage processing shapes the way cows spend their day. Every extra minute devoted to eating is time unavailable for resting and rumination, two behaviors increasingly recognized as fundamental to rumen health, welfare and productivity.
Speaking during Balchem’s Real Science Lecture Series, Grant introduced what he calls precision chewing management, describing it as “precisely meeting her needs for the big three behaviors: eating, resting and ruminating.”
The concept shifts the focus away from forage particle size alone and toward the cow’s daily time budget. If eating becomes more efficient, cows gain more opportunity to rest and ruminate. If eating becomes excessively time-consuming, those hours have to come from somewhere else.
Healthy Rumens Begin with Lying Down
Rumination has long been recognized as an indicator of rumen function, but posture may be just as important as duration.
According to Grant, “over 80% of rumination in an ideal world for the cow should occur while she’s lying down.”
That recommendation reflects more than cow comfort. While lying in sternal recumbency, cows produce more saliva during rumination, helping buffer rumen contents while also allowing for the physiological rest that accompanies this behavior.
Recumbent rumination has also been linked with improved rumen health and production. Cows that spend more time ruminating while lying down have been observed to maintain a higher rumen pH, consume more dry matter and produce milk with greater fat and protein percentages. In unpublished Miner Institute work, rumination while lying down shows the strongest behavioral correlation with milk fat.
The implications extend well beyond nutrition. Lameness, overcrowding, inadequate stall comfort and heat stress all reduce opportunities for cows to lie down, potentially influencing one of the behaviors most closely associated with rumen function.
When Coarse Forage Steals Resting Time
If lying rumination is the goal, the next question becomes whether ration formulation is helping or hindering cows from getting there.
According to Grant, as physically effective fiber increases, cows spend dramatically more time eating. In recently conducted research, an eating time increase of approximately 107 minutes per day only resulted in a rumination increase of about 35 minutes. Total chewing time increased by more than two hours, but nearly all of that additional time came at the expense of resting.
Why?
As Grant explains, “The cow spends the time at the feed bunk to reduce whatever the particle size is in the ration before she swallows it.”
In other words, excessively coarse forage asks cows to perform work that could have been accomplished mechanically before feed reached the bunk.
Longer eating times do not necessarily translate into healthier rumination. Instead, prolonged eating may simply leave fewer hours available for resting and recumbent rumination.
Grant suggests eating behavior is most efficient when cows consume their daily ration within roughly three to five hours. Beyond that point, additional eating time begins competing with behaviors that support rumen health and overall welfare.
The Rumen Starts at the Feed Bunk
One of Grant’s most practical take-home messages is that cows naturally create the particle size they need.
Cows reduce forage particles substantially during eating, producing swallowed feed particles that average approximately 8 to 12 millimeters across a variety of forage sources.
“We’re really trying to mimic the cow when chopping forages,” Grant says.
That philosophy supports a more dynamic approach to forage processing. Rather than relying on one fixed theoretical length of cut, Grant recommends adjusting chop length according to forage maturity, moisture content and indigestible fiber characteristics. As uNDF240, the amount of neutral detergent fiber that remains undigested after 240 hours in a cow’s rumen, increases with forage maturity or growing conditions, chopping somewhat finer can maintain eating efficiency without sacrificing rumination. Chopping too finely, however, can accelerate passage rate and reduce rumination.
Precision Feeding Becomes Preventive Medicine
Precision chewing management ultimately extends beyond nutrition.
Grant emphasizes that forage particle size represents only one component of the system. Even a well-balanced ration cannot achieve its intended effect if overcrowding, poor bunk access, uncomfortable stalls or heat stress prevent cows from expressing normal eating and resting behaviors.
As he summarizes, producers should “optimize forage particle size from the cow’s perspective, because that’s the only perspective that matters.”
That perspective also points toward the future. Grant envisions forage management becoming increasingly dynamic, with chop length adjusted according to forage maturity, moisture content and indigestible fiber. He even suggests that future harvest equipment may one day adjust theoretical length of cut automatically as crop characteristics change.
The larger message is that chewing behavior may deserve greater attention as an animal health metric. Optimizing forage particle size is not simply about processing feed. It’s about helping cows spend less time eating, more time lying down and ultimately creating the conditions that support a healthier rumen.
