Characterization of Frost-Damaged Immature Soybeans for Alfalfa and Alfalfa-Brome Hay, Corn Silage or Corn Based Diets

One compositional study and three single stage in vitro rumen fermentation experiments were conducted to characterize the feeding profile of frost-damaged immature soybeans (FDIS). Dauson and Dassel soybean plants were harvested at 86, 93, 100, 107 days post-planting and frozen at -5 C to contrast with natural frozen soybeans of the same varieties that were serially planted and harvested after the first killing frost. No differences between soybean variety were detected for crude protein (CP), ether extract (EE) or dry matter content (DM). Crude protein and EE content differed (P\u3c.05) between maturities of artificially frozen (AF) soybeans. Only the EE content differed (P\u3c.01) with maturity of naturally frozen (NF) soybeans. Planting date had an effect (P\u3c.001) on composition of mature soybeans primarily due to increasing EE component. Exp. 1. Five levels of FDIS (0, 5,10, 15, 20%). three substrates (alfalfa hay, ALF), corn silage (CS), ground corn (WSC)) and two fermentation times (24 or 48 hours) were evaluated in single stage in vitro fermentations. FDIS supplementation had no effect on in vitro dry matter disappearance (IVDMD) of ALF or USC, indicating at the upper limit of FDIS supplementation had not been reached. IVDMD of corn silage was depressed (P\u3c.01) when FDIS exceeded 10%. Increasing levels of FDIS increased NH –N (P\u3c.01) but had no effect on VFA concentration in fermentation liquor. Exp. 2. Alfalfa-brome hay, ALF and CS were supplemented with FDlS for 48-hour IVDMD comparisons. IVDMD was not affected by substrate, but FDIS increased IVDMD of CS (P\u3c.001). Exp.3. Four treatments, soybean meal (SBM), heated mature raw soybeans (HMB), heated FDIS (HFDIS) and FDIS, were used to differentiate oil content and trypsin inhibitor effects on roughage fermentation. Only SBM increased IVDMD (P\u3c.05) of forages tested. FDIS included at 20% of the DM did not significantly decrease IVDMD of forages in most instances but may not stimulate digestion in the same manner as SBM