Effects of corn silage crop processing and chop length on intake, digestion, and milk production were evaluated. Corn silage treatments were harvested at one-half milkline stage of maturity (65% whole-plant moisture content) and at 0.95-cm theoretical length of cut without processing (control) or 0.95-, 1.45-, or 1.90-cm theoretical length of cut with processing at a 1-mm roll clearance. Twenty-four multiparous Holstein cows averaging 71 d in milk at trial initiation were in a replicated 4 x 4 Latin square design with 28-d periods; one square was comprised of ruminally cannulated cows for rumen measurements. Corn silage treatments were fed in total mixed rations containing 50% forage (67% corn silage and 33% alfalfa silage) and 50% corn and soybean meal based concentrate (dry matter basis). Dry matter intake (25.9 vs. 25.3 kg/d) and milk (46.0 vs. 44.8 kg/ d) and fat (1.42 vs. 1.35 kg/d) yields were higher for the processed corn silage treatments compared with the control corn silage. Within the processed corn silage treatments, there were no chop length effects on intake, milk production, or milk composition. Chewing activity was not different among the four corn silage treatments averaging 12 h/d. Total tract digestion of dietary starch was lower for control corn silage (95.1%) compared with fine, medium, and coarse processed corn silage treatments, which averaged 99.3%. Total tract digestion of dietary NDF was reduced for fine-processed corn silage compared with control corn silage and coarse-processed corn silage (28.4% vs. 33.9 and 33.7%, respectively). Processing corn silage improved dry matter intake, starch digestion, and lactation performance. Under the conditions of this study and with theoretical lengths of cut ranging from 0.95 to 1.90 cm, length of chop effects were minimal in processed corn silage.

N orth American dairy farmers are showing increasing interest in processing whole-plant corn silage (WPCS) with roll processors onboard the forage harvester. Although commonly utilized in Europe for years, the practice was virtually ignored in North America. This lack of interest could be traced to the following causes. First, nutritional research in North America with beef and dairy animals had not shown improved animal performance with processed corn silage diets (Miller et al., 1969; Rojas-Bourrillon et al., 1987). These researchers harvested both the control and processed crop at a theoretical length-of-cut (TLC) of 3 to 10 mm. By cutting at a short TLC and then processing, the quantity of fine material in the diet was increased such that depressed fiber digestion may have counteracted any improvement in starch digestion. Second, there was a decade long decline in the total North American production of corn silage (Shinners, 1997). Third, there was a lack of availability of processing systems on pull-type forage

Crop processors on forage harvesters have become readily available and widely used by North American livestock producers. Past research has shown that intensive mechanical processing at the time of cutting can improve the fiber digestibility of alfalfa and grasses, and questions have surfaced as to the potential effectiveness of a crop processor on a forage harvester to also improve the animal utilization of wilted forages. Processing wilted alfalfa with crop processing rolls was effective in increasing the level of plant tissue disruption, as quantified by leachate conductivity, by more than 30% in all cases and similarly reduced particle-size from the theoretical-length-of-cut. Processed material was visibly darker and more bruised than control treatments. Processor roll clearance and cutterhead theoreticallength-of-cut had a greater effect on crop physical properties than did processing roll speed difference. Processing wilted alfalfa increased harvester energy requirements by 36 to 113% depending upon crop moisture and the feeding characteristics of the processing rolls as affected by the aggressiveness of the tooth profile. Processing wilted alfalfa increased the crops in situ dry matter disappearance at 12 and 24 h by greater than six percentage units and increased the instantly soluble fraction by up to seven percentage units. However, processed alfalfa did not affect lactation performance of Holstein dairy cows.