Feeding processed or rolled corn silage is gaining in popularity across the U.S., because of more widespread custom harvesting using self-propelled choppers and the marketing of pull-type choppers fitted with crop processors.

Johnson and co-workers (1996) reported that rolling increased milk yield 2.0 lb/cow/day, increased milk protein yield, and reduced corn kernel passage into the manure. An early trial at the U.S. Dairy Forage Research Center (Prairie du Sac, WI) showed about the same milk production response, but in a later trial (Bal and co-workers, 1998b) rolling was not beneficial.

We (Bal and co-workers, 1998a and 1999) recently completed a feeding trial at our UW Arlington Dairy Cattle Center to evaluate corn silage crop processing and chop length effects on lactation performance. The results are presented in Table 1.

Pioneer hybrid 3563 was harvested as whole-plant corn silage at ½ ML stage of maturity. The control corn silage was chopped at 3/8" TLC without rolling using a pull-type chopper. Treatment corn silages were harvested at 3/8 ", 9/16", and ¾" TLC and rolled using the same pull-type chopper fitted with a crop processor. The crop processor was set at less than one-millimeter roll spacing for all three chop lengths. Experimental silages were stored in silo bags, and averaged 33% whole-plant DM with little variation across treatments on feed-out.

Twenty-four mature Holstein cows averaging about 100 DIM at the start of the feeding trial were used in a replicated Latin Square design with monthly periods. Four of the cows were ruminally cannulated to facilitate rumen pH, fiber-mat formation, and digestion measurements. All diets were fed as TMR containing half forage of which two-thirds was one of the treatment corn silages and one-third was alfalfa silage (DM basis). All diets were formulated to 18% CP (DM basis) and to meet or exceed NRC guidelines for minerals and vitamins.

Mean particle length (MPL) of corn silage was measured using the Wisconsin Oscillating Screen Particle Separator. Rolling reduced MPL of the 3/8" TLC corn silage from 9.4 to 6.7 mm. Chopping rolled corn silage at 9/16" or 3/4" TLC increased MPL to near the length of the unrolled silage. Rolling reduce the percentage of coarse particles in the 3/8" TLC corn silage from 7.5% to 1.5%. This resulted in a lower percentage of coarse particles in the TMR for cows fed the 3/8" TLC-rolled silage (3% versus 6%).

Table 1. Impact of crop processing and chop length on corn silage utilization by dairy cows (Bal and co-workers, 1998a and 1999).

Percentage of coarse particles was measured as the proportion of the silage or TMR retained on the top two screens of our separator. This is roughly comparable to the proportion that would be retained on the top screen of the Penn State – Nasco shaker box. Chopping rolled corn silage at 9/16" or 3/4" TLC increased the percentage of coarse particles to 10% and 21.5%, respectively. This resulted in a higher percentage of coarse particles in the TMR for cows fed these silages (6% and 10.5% for 9/16" and 3/4" TLC diets, respectively).

An interesting observation was that the coarse fraction in the unrolled silage contained a high proportion of whole and half cobs prone to sorting in the feed bunk. On the other hand, the coarse fraction in the coarsely chopped rolled silages had no cob material and was comprised primarily of precision-chopped stover. No unbroken corn kernels were found in the rolled silages.

Cows fed the rolled silages on average ate 1.5 pounds more diet DM each day than cows fed unrolled silage. Cows fed the rolled silages on average produced 2.5 pounds more milk and 3.5 more FCM each day than cows fed unrolled silage. Milk fat test was .10% units higher on average for cows fed the rolled silages. This improvement in milk fat test with rolling was unexpected, but may have resulted from less sorting of the cob fiber in the feed bunk for the rolled-silage diets. There were no differences in dry matter intake, milk yield, or milk composition among the rolled-silage diets.

Cows ruminated about eight hours per day and this did not differ among the four treatments. Ruminal pH did not appear to differ among the four treatments. Our measure of fiber-mat formation in the rumen revealed a drop off for the 3/8" TLC-rolled silage compared with the unrolled silage. Chopping the rolled silage at 3/4" TLC brought this parameter back to what we observed for the unrolled silage. It is unknown whether this would have proved beneficial for preventing digestive disorders in fresh cows or in a longer-term study. Ruminal 24-hour macro-bag dry matter digestion was higher on average for the rolled silages.

Rolling corn silage that was harvested at ½ ML with 67% whole-plant moisture improved milk and fat production. Rolling corn silage chopped at a 3/8" TLC reduced its MPL and coarse particle fraction and tended to lower our measure of rumen fiber-mat formation. While this did not adversely affect rumination activity, feed intake or lactation performance in this trial, there may be cause for concern in fresh cows diets or in a longer-term lactation trial.

We recommend a 3/4" theoretical length of cut setting on the chopper for rolled corn silage at this time for several reasons. Feed intake and lactation performance were excellent for this coarsely chopped silage. Observed trends in particle length and rumen fiber-mat formation may prove beneficial in certain feeding situations. Power requirements for rolling and chopping will be lower and material throughput higher for the coarsely chopped silage.

Rolls should be set and maintained at a 1 mm spacing so that kernel and cob breakage is complete. In some cases, particularly with wet silages, the roll clearance may be expanded to 2 mm or 3 mm; Shinners (personal communication) reported 91% broken kernels at 3 mm roll clearance with ½ ML silage chopped at ¾" TLC.

We can not support chopping at lengths greater than 3/4" TLC at this time for several reasons. We have no evidence that coarse chopping of corn silage greatly improves animal performance. There have been reports from the field about excessive equipment wear when chopping rolled silages at one-inch or greater TLC.

Also, we are concerned about adequate packing of coarsely chopped silage in the silo and the quality of the ensuing fermentation process. Data in Table 2 (Novak and co-workers, 1999) shows considerable variation in MPL and horizontal-silo packing density for processed corn silages on commercial dairies. It appears that we can improve upon the chopping/rolling currently being done commercially.

Table 2. Variation in mean particle length and horizontal-silo packing density for processed corn silages on 84 commercial Wisconsin dairies (Novak and co-workers, 1999).

Item	Average	Range	Standard Deviation
All samples, n=85
DM %	35.5	25.5 – 57.3	6.9
MPL, mm	12.5	6.5 – 19.8	2.5
Coarse Particles, %	28.9	4.4 – 58.8	15.1
Subset, n=38
DM %	34.2	25.5 – 47.7	6.7
MPL, mm	12.5	8.5 – 17.5	2.2
Coarse Particles, %	28.1	4.9 – 58.8	14.2
Packing density, lb DM/cu. ft.	11.9	8.6 – 18.3	2.0

It is often assumed in the field that crop processing is the salvation if BL corn silage is harvested, and at times it is even promoted that way. Data in Table 3 shows the impact of crop processing on ruminal In situ macro-bag dry matter, NDF, and starch degradation in early and late chopped corn silage (Bal and co-workers, 1998c).

Table 3. Impact of crop processing on ruminal In situ macro-bag dry matter, NDF, and starch degradation in early and late chopped corn silage (Bal and co-workers, 1998c).