Particle length is still a big concern in dairy feeding Talk about making a big splash in a relatively short time. Developed four years ago by researchers looking to bring laboratory methods for measuring forage and total mixed ration (TMR) particle sizes to the farm gate, the Penn State forage particle separator has rapidly become a "must use" piece of equipment for dairy producers and their nutritionists.

"Our policy here is to never leave the office for a farm visit without making sure it's in the car," says University of Illinois dairy specialist Mike Hutjens.

Driving the need for the new tool were basic changes in dairy cow feeding. High-producing cows require more energy, leading to rations with higher levels of concentrates. The trend was pushed along by changes in harvesting and feeding equipment and feed storage facilities on many dairies. For example, shorter particle length promotes better packing and cleaner faces in bunker silos and also poses fewer clogging problems for vertical silo unloaders and TMR mixers.

What hasn't changed is the dairy cow's need for adequate fiber. When minimum fiber levels aren't met, total dry matter digestibility can be reduced, milk fat percentage can taper off and cows can develop rumen acidosis and other health problems.

"It's been demonstrated that reduced forage particle size decreases the time a cow spends chewing and causes a trend toward decreased rumen Ph," says Penn State University's Jud Heinrichs, a member of the research team that developed the separator. "When cows spend less time chewing, there's a decrease in the production of saliva needed to buffer the rumen."

As the separator has become more widely used, there's been an evolution in the thinking of producers and nutritionists on how to best put it to work. Some of the key concepts:

- Check particle length for individual forages during harvest. Making periodic checks while chopping and adjusting harvesting equipment accordingly is sound strategy, says University of Wisconsin dairy specialist Lou Armentano.

"The material going into the forage wagon won't get any longer once it goes into storage," he says.

The table on page 7 shows University of Illinois guidelines for particle length for various forages and TMRs.

- Sample again before delivering feed to the bunk. Measuring the particle length of individual forages going into the silo is only part of the feeding job.

"It's similar to analyzing a forage for crude protein," notes Heinrichs. "There are recommended ranges for individual forages, but the real use of the measurement is in combining forages to achieve the proper particle size in the total ration, much like combining feeds to achieve the proper protein in the ration."

Armentano offers a similar reason for sampling before feeding.

"The material that's put into the silo isn't necessarily the same material that's delivered to the feed bunk," he says. "Silo unloaders can grind forages and TMR mixers can reduce particle size if you overmix."

- Watch for sorting. The negative impacts of feeding a TMR that's deficient in particle length get lots of attention. But it's also possible to load up a TMR with forage particles that are too long. The big problem: Cows can sort or nudge out the long particles and eat just the tasty stuff in the ration.

Hutjens points to the example of an Illinois dairyman who corrected a low milkfat test by mixing hay longer in the TMR mixer, reducing the amount of feed in the top box of the particle separator from 18% to 12%.

"Anytime you get over 13% of the TMR in the top box, you need to monitor cows and the TMR for evidence of sorting," says Hutjens. "For the bottom box, we recommend targeting less than 30%."

- Take a closer look at the middle box. When the particle separator was introduced, most emphasis was placed on the percent of feed remaining in the top box, i.e., making sure that the TMR contained enough long fiber. Two years ago, the bottom box was getting most of the attention.

"Now a lot of people are thinking that the middle box is the most critical," says Hutjens. "That's where you find the material that provides fiber length, more surface area for bacterial attachment to feed particles and that slows the rate of feed passage. We've seen several high-producing and healthy herds in Wisconsin where the TMR measured only 4-8% in the top box, but nearly 30% in the middle box."

The bottom line, says Hutjens, is that you need to review all three boxes when evaluating the TMR.

- Adjust for wetter feeds. Wet feed ingredients like wet brewer's grain or wet gluten feed add water to the ration and need to be taken into account when you're sampling TMRs with the particle separator.

"In an ideal setting, you'd make calculations on a 100% dry matter basis," says Hutjens. "But that would require more equipment like a couple of microwave ovens or moisture testers and additional time. It's not going to happen on a commercial dairy. The important thing is to adjust values when you're using wet feed. For example, 6% dry hay in the top box can be equivalent to 12% wet haylage particles in the top box."

The Penn State forage particle separator is commercially available through Nasco in Ft. Atkinson, WI. Price on a basic unit is around $175. For a unit with scales and containers, cost is in the neighborhood of $215.

"I don't know if every dairy producer with a TMR needs to own one," says Hutjens. "But every producer should at least have access to one."