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Quality Estimates and Chemical Characterization of Fermented and Unfermented Summer Annual Forages¹

Livestock enterprises require forage crops that provide feed during or after midsummer. Ten cultivars representative of forage and grain sorghums [Sorghum bicolor (L.) Moench], sorghum x sudangrass (Sorghum vulgare sudanense) hybrids, and millet [Pennisetum americanum (L.) Leeke] that provide forage during this time of the year were evaluated for quality and fermentation characteristics. Chemical and bioassay measurements were compared prior to and after fermentation.

Fermentation patterns were altered by sample handling. Expulsion of air from plastic fermentation bags by simply hand pressing or removal or air in the field by vacuum produced satisfactory silage for experimental purposes. Additional handling in the laboratory to heat seal was undesirable as it significantly increased pH and lactic acid concentrations and reduced titratable acidity.

Fermentation generally reduced differences in IVDMD among cultivars within major types in the unfermented forage. Both N and crude fiber (CF) concentrations in oven-dried samples generally were higher in fermented than in unfermented forage, but no difference was noted between 45 and 90 days of fermentation. Water-soluble carbohydrate (WSC) levels were significantly altered by the drying method and fermentation. The WSC levels for unfermented forage and that fermented 45 and 90 days were 16.7, 6.6, and 7.6%, respectively. The WSC levels averaged 19.8% in unfermented freeze-dried forage and 13.7% in unfermented oven-dried forage. The WSC levels for fermented freeze-dried forage were similar to those for oven-dried forage (7.5 vs. 6.7%). The WSC percentages in the freeze-dried, unfermented forage was not significantly correlated with either acetic or lactic acid production in 45-day freeze-dried fermented forage (r = 0.67 and 0.54, respectively), but were significantly correlated with titratable acidity (r = 0.93**). There was no indication of improved quality in fermented forage for which the WSC concentration was high in the unfermented tissue. Total digestible nutrients (TDN), computed from CF, averaged 58.2,57.0, and 56.9% for the oven-dried unfermented and 45 and 90-day fermented silages, respectively, compared with IVDMD percentages of 52.6,45.1, and 46.0.

Key Words: Forage sorghum • Grain sorghum • Sorghum hybrids • Millet • IVDMD • Water soluble carbohydrates • Crude fiber • N • Tannin • Oven-dried • Freeze-dried • Silage transformations

² Plant physiologist, USDA, SEA-AR and professor of crop science; and extension agronomist, Mississippi State Univ., State College, Miss. 39762.

Received for publication September 22, 1980.