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Survery: Forage Particle Length Usually OK–Until It Hits The Mixer

Most dairy producers did a good job of chopping haylage and corn silage to the recommended particle length, but forages often lost their “tickle factor” by spending too much time in the total mixed ration mixer, according to a survey by Irv Possin, Fond Du Lac County dairy/livestock agent.

TMR mixers ran four or five times longer than manufacturers” recommendations, Possin reports. Auger mixers ran an average of 13 minutes, and tumbler mixers ran about 20 minutes. When mixing time exceeded 15 minutes, particle length decreased by 36 percent. Producers said they let the mixers run during ingredient fill and during travel time to the bunk. Forage particle length can be increased by adding some baled hay — just don”t let the mixer run for 20 minutes after you add the hay, Possin points out.

Most farms chopped forage to recommended lengths. Average mean particle length (MPL) in both haylage and corn silage was 0.31 inch, above the UW minimum recommendation of 0.25 inch. Long particles (1.5 inches or longer) were close to minimum recommendations: about 15 percent for haylage and 13 percent for corn silage. “Ideally, we”d like to see those numbers at 25 percent,” Possin says.

As haylage became drier, particle size decreased, Possin found. Also, as producers switch from upright silos to bag, bunker or stack storage, MPL and percent of long particles increased. Producers sometimes chop silage for the benefit of their silo unloaders, rather than for the benefit of their cows, Possin notes. Mean particle length was 0.47 inches from bunker silos, but 0.3 inch from upright silos. Farmers often said they chopped the silage shorter for uprights so the unloader would throw it out better.

Possin found more laminitis (lameness) when TMRs were finely chopped. Turnover was higher in high-laminitis herds, probably because the lame animals were culled, Possin says. The high-laminitis herds also had less forage dry matter in the diet (43 percent versus 50 percent for the low-laminitis herds). He thinks that the low forage content, along with reduced particle length, may have had an additive effect on the incidence of laminitis. Possin found no association between MPL and displaced abomasum or ketosis in TMR or non-TMR herds. However, displaced abomasums were more common in a few herds with extremely short particle lengths, Possin says.

Particle length influenced production and fat test. As MPL increased, rolling herd average increased. MPL was 0.33 inch in the top 25 percent fat test herds, 0.28 inch in the bottom 25 percent. In other words, herds with low fat test had lower MPL and lower percentage of long particles.

More chopper knives didn”t always produce more finely chopped forage, Possin reports. Feed roller speed, which controls length of cut is a major factor, he says. In this study, as length of cut increased, MPL and percent of long particles increased. Other factors affecting particle length include knife sharpness, shear bar/knife clearance, recutter screens, and the amount of material reaching the feed rollers.

Possin and his colleagues surveyed 49 dairy farms in Fond Du Lac County. The herds ranged from 21 cows to 862 cows, and producers fed both TMR and topdressed rations. They targeted some herds that had high rates of metabolic disorders. Average production ranged from 15,800 pounds to more than 25,000 pounds. They analyzed haylage, corn silage and TMR samples that came from upright, bunker and bag silos.