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.

Whole-plant corn was harvested at early dent, quarter milkline, two-thirds milkline, and black layer stages to evaluate the effects of maturity on intake, digestion, and milk production when corn was fed as silage in the diet. Twenty multiparous Holstein cows were used in a replicated experiment with a 4 x 4 Latin square design with 28-d periods. Diets containing 50% forage (67% corn silage and 33% alfalfa silage) and 50% concentrate (dry matter basis) were fed as total mixed rations. Moisture contents were 69.9, 67.6, 64.9, and 58.0% for silages from corn harvested at early dent, quarter milkline, two-thirds milkline, and black layer stages, respectively. Intakes of dry matter were similar across the four treatments and ranged from 3.73 to 3.79% of body weight. Milk production was highest (33.4 kg/d) for cows fed silage from corn harvested at the two-thirds milkline stage and lowest (32.4 kg/d) for cows fed silage from corn harvested at the early dent stage. Milk protein production was highest for cows fed silage from corn harvested at the two-thirds milkline stage (1.17 vs. 1.12 to 1.13 kg/d). Apparent total tract digestion of dry matter, organic matter, crude protein, acid detergent fiber, and starch was lowest for cows fed silage from corn harvested at the black layer stage. Although starch intake was similar for cows fed silage from corn harvested at the two-thirds milkline stage and for cows fed silage from corn harvested at the black layer stage (9 kg/d), intake of digestible starch was 0.4 kg/d lower for cows fed silage from corn harvested at the black layer stage. The optimum stage for corn that was ensiled was two-thirds milkline with some flexibility between quarter and two-thirds milkline.

Maize (Zea mays L.) stover has been identified as an important feedstock for the production of cellulosic ethanol. Our objectives were to measure hybrid effect and combining ability patterns of traits related to cellulosic ethanol production, determine if germplasm and mutations used for silage production would also be beneficial for feedstock production, and examine relationships between traits that are relevant to selective breeding. We evaluated grain hybrids, germplasm bred for silage production, brown‐midrib hybrids, and a leafy hybrid. Yield and composition traits were measured in four environments. There was a 53% difference in stover yield between commercial grain hybrids that were equivalent for other production‐related traits. Silage germplasm may be useful for increasing stover yield and reducing lignin concentration. We found much more variation among hybrids than either in vitro ruminal fermentability or polysaccharide concentration. Correlations between traits were mostly favorable or nonexistent. Our results suggest that utilizing standing genetic variation of maize in breeding programs could substantially increase the amount of biofuels produced from stover per unit area of land.

Gains in corn (Zea mays L.) grain yield over time are well documented, but corresponding changes in forage and stover yield and quality have received less attention. Our objective was to describe yield and quality changes of representative cultivars used by farmers in the northern Corn Belt. Six open‐pollinated cultivars used prior to 1930, 24 cultivars representing four 15‐yr eras between 1931 and 1990, and six modern cultivars, for a total of 36 cultivars, were divided into early‐ and late‐maturity trials. Each trial was grown at three locations in Wisconsin during 1997 and 1998. Since 1930, corn forage dry matter yield has increased at the rate of 0.128 to 0.164 Mg ha−1 yr−1 with stover dry matter yields increasing at the rate of 0.043 to 0.054 Mg ha−1 yr−1 Forage crude protein has not changed significantly with time. Forage neutral detergent fiber concentration has decreased 0.825 to 0.948 g kg−1 yr−1, while forage in vitro digestibility increased 0.538 to 0.612 g kg−1 yr−1 Stover neutral detergent fiber concentration and in vitro digestibility have not changed over time. Since 1930 forage, stover, and ear yield have increased 1.4, 0.7, and 2.4% yr−1, respectively. This trend will no doubt continue, but greater progress might be made if corn forage breeding improvement concentrates on yield and quality changes in stover.

Determining the proper time to harvest corn (Zea mays L.) for whole plant silage is difficult for growers. The objective of this study was to determine the relationship between kernel milk‐line position and whole plant yield, quality, and dry matter (DM) content. Our goal was to develop a means to predict the optimum stage for harvesting corn for silage. Four early maturity (85 d) hybrids were evaluated for yield, forage quality, and DM content at five stages of kernel maturity, including: soft dough (SD) (dents first visible); early dent (ED) (dents visible on 95% of kernels); 1/2 milkline (1/2 ML) (milkline positioned half‐way between the tip and base of the kernel); 3/4 milkline (3/4 ML) (milkline positioned 3/4 of the way from tip to base); and no milkline (No ML) (milkline no longer present in kernel) over 3 yr (1988–1990) in north central Wisconsin. Whole plants, stover, and ears were harvested before killing frosts, except in 1989 when plants were frozen shortly after 1/2 ML. Whole plant DM content was within the optimum range for silage harvest (30 to 40%) when corn plants were between the 1/2 and 3/4 ML stages. Maximum whole plant yield was reached by 1/2 ML, while grain yield reached maximum levels by 3/4 ML. Whole plant neutral detergent fiber (NDF) and acid detergent fiber (ADF) decreased an average of 7.6 and 4.4 percentage units from SD to 1/2 ML and then increased at the No ML stage. Whole plant in vitro dry matter disappearance (IVDMD) was greatest between ED and 3/4 ML. Whole plant and stover crude protein (CP) concentration declined at each successive harvest stage from SD to No ML. Early season hybrids can be harvested for silage between 1/2 and 3/4 ML for maximum whole plant yield and optimum quality and DM content. Kernel milkline position was a good indicator of optimum harvest stage for this range of kernel maturities. Research Question In the North Central states, a high proportion of corn (Zea mays L.) harvested for silage is planted in the extreme northern part of the region, where adapted hybrids range from 70 to 90 d relative maturity (RM). When growing corn intended for silage use, critical factors which influence optimum harvest timing include whole plant dry matter (DM) content, total yield, and nutritional quality. Determining the proper maturity to harvest corn for whole plant silage is difficult for growers. The objective of this study was to determine the relationship between kernel milkline position and whole plant yield, quality, and dry matter content. Our goal was to develop a means to predict the optimum stage for harvesting corn silage. Literature Summary Estimates of whole plant DM content in corn frequently are based on grain maturity. Researchers in Minnesota demonstrated that kernel milk‐line position was a reliable and useful visual indicator of grain maturity and whole plant DM content. Several investigations have evaluated corn whole plant DM accumulation and nutritive value at various stages of crop maturity. Maximum whole plant yield is generally reported to occur...

L arge increases in maize (Zea mays L.) stover yield are required for the United States to displace a signifi cant fraction (e.g., 30%) of its petroleum consumption with biofuels under an agricultural framework similar to that currently in place (Perlack et al., 2005). Substantial genetic variation for stover yield exists (Lorenz et al., 2009) and could be exploited for this purpose through breeding and selection. Maize breeders have been highly successful in increasing grain yield of maize since the 1930s (Duvick et al., 2004); this rate of gain should be maintained or exceeded. Besides grain's value as a food commodity, grain yield will continue to drive hybrid seed sales because grain is more practical to transport and store, it has higher energy content, and the conversion effi ciency of grain to ethanol is close to 100% using already established production practices (Dhugga, 2007). The conversion effi ciency of stover, on the other hand, is 65% or less using currently feasible technology (Lynd et al., 2008;Olofsson et al., 2008). Also, the conversion of stover to ethanol is several times more expensive than converting grain to ethanol, which cancels the lower cost of stover relative to grain as a source of biofeedstock (McAloon et al., 2000;Lynd et al., 2008).Given that grain yielding ability will obviously continue to be critical and high stover yield for energy markets might be desirable as well, total biomass yield of maize could be increasingly important and could replace grain yield as the primary trait for selection ABSTRACT The use of maize (Zea mays L.) stover as a feedstock for cellulosic biofuels production will create demand for maize hybrids with greater stover yield. It is expected that grain yield will remain the most critical trait and continue to drive hybrid sales, requiring that any increases in stover yield be made without sacrifi cing grain yield potential. The objective of this review was to determine the relationship between grain yield, harvest index, and stover yield to illuminate the potential for increasing both grain and stover yield through breeding. In contrast to what has been observed in other crops, gains in maize grain yield over time in the U.S. Corn Belt have been accompanied by increases in stover yield. Where recurrent selection on grain yield has been most successful, stover yield also increased while harvest index has been relatively stable. The opposite situation has been observed in tropical germplasm, where gains in grain yield have been associated with increasing harvest index and relatively constant biomass yield. We expect that stover yield of Corn Belt hybrids will continue to increase along with grain yield, resulting in future hybrids capable of producing both more food and biofeedstock for energy production. If maize breeders pursue selection for increased stover yield, we found no evidence to suggest that breeding for stover yield will necessarily reduce rate of gain in grain yield.

An understanding of the factors and relationships affecting wholeplant digestibility is needed to improve the nutritional quality of maize (Zea mays L.) forage. The objectives of this study were to: (i) determine the ranges among 24 maize genotypes for fiber composition and digestibility of stover and whole-plant forage, and (ii) determine the relationships between fiber composition and digestibility. Twenty-four S 0 ., families (S 0-derived families in S,) exhibiting a range in neutral detergent fiber (NDF) and lignin at mid-flower, were testcrossed to two commercial inbred lines (FR23 and LH74) to form two groups of F, hybrids. A third experimental group was created by self-pollinating the S 0 .i families to form S 0. 2 families. These germplasms were evaluated in three Wisconsin environments. Ranges in S,. 2 family means for fiber and digestibility were: NDF, 439 to 582 g kg-1 for the whole plant and 579 to 654 g kg-1 for the stover; and in vitro true digestibility (IVTD), 714 to 820 g kg-1 for the whole plant and 689 to 757 g kg-1 for the stover. Narrower ranges were observed among LH74 and FR23 testcrosses. For S,. 2 families, correlation coefficients for stover IVTD with stover NDF and lignin were-0.76 and-0.85, respectively. Correlation coefficients for whole-plant IVTD with stover IVTD and lignin of S 0. 2 families were 0.44 and-0.49, respectively. The results of this study show that (i) significant variation exists for nutritional quality traits of the stover and whole-plant forage and (ii) stover quality is an important factor influencing whole-plant nutritional quality within the germplasm studied.

Maize silage is a significant energy source for animal production operations, and the efficiency of the conversion of forage into animal mass is an important consideration when selecting cultivars for use as feed. Fiber and lignin are negatively correlated with digestibility of feed, so the development of forage with reduced levels of these cell-wall components (CWCs) is desirable. While variability for fiber and lignin is present in maize germplasm, traditional selection has focused on the yield of the ear rather than the forage quality of the whole plant, and little information is available concerning the genetics of fiber and lignin. The objectives of this study were to map quantitative trait loci (QTLs) for fiber and lignin in the maize stalk and compare them with QTLs from other populations. Stalk samples were harvested from 191 recombinant inbred lines (RILs) of B73 (an inbred line with low-to-intermediate levels of CWCs) x De811 (an inbred line with high levels of CWCs) at two locations in 1998 and one in 1999 and assayed for neutral detergent fiber (NDF), acid detergent fiber (ADF), and acid detergent lignin (ADL). The QTLs were detected on nine chromosomes, mostly clustered in concordance with the high genetic correlations between NDF and ADF. Adjustment of NDF for ADF and ADF for ADL revealed that most of the variability for CWCs in this population is in ADF. Many of the QTLs detected in this study have also been detected in other populations, and several are linked to candidate genes for cellulose or starch biosynthesis. The genetic information obtained in this study should be useful to breeding efforts aimed at improving the quality of maize silage.