In Situ Degradation Kinetics of Inoculant Treated Sorghum Silage.

In situ degradation kinetics of inoculant treated sorghum silage

M.E. Thomas¹, J.L. Foster^1,2, K.C. McCuistion³, L.A. Redmon¹, R.W. Jessup¹

¹Department of Soil and Crop Sciences, Texas A&M University College Station, TX; ²AgriLife Research, Texas A&M University, Beeville, TX;³King Ranch Institute for Ranch Management, Texas A&M University Kingsville, TX.

The purpose of this study was to determine if sorghum (Sorghum bicolor) silage pretreated with fibrolytic enzyme (xylanase plus cellulase: XC) or microbial inoculant [Promote ASB (Lactobacillus buchneri and L. plantarum); Pro] has greater extent and faster rate of dry matter (DM) and fiber degradation. This completely randomized factorial experiment (cultivar  inoculant) included 2 cultivars [Silo 700 (Silo) and MMR 381/73 (MMR)] and 3 inoculants (control, XC and Pro). Inoculant (1.34 ml XC or 16.5 mg Pro) was added to 200 ml distilled water (control) and applied to 5 kg of chopped sorghum prior to ensiling. Three ruminally fistulated steers (453 kg BW) were used for the study. The trial began after a 10-d adaptation to 8 kg hd^-1 d^-1 sorghum-sudan (S. bicolor) hay and 1.7 kg hd^-1 d^-1 cotton seed meal. Water and mineral were provided ad libitum. Ruminal incubation times included 0, 4, 8, 16, 24, 48, and 72 h. Pre- and post-in situ samples were analyzed for DM, neutral detergent fiber (NDF), and acid detergent fiber (ADF). The wash DM fraction was not different between cultivars and was greater (P < 0.05) for control than Pro. The wash NDF and ADF fractions were greater (P < 0.01) for Silo than MMR. The wash NDF fraction of control Silo was greater (P < 0.04) than Silo treated with XC. The potentially degradable DM, NDF, and ADF fractions were greater (P < 0.01) for Silo than MMR and greater (P < 0.02) for control than XC. Undegraded DM fraction was greater (P < 0.01) for Silo than MMR, and greater (P < 0.02) in untreated sorghum silage than that treated with XC. Control Silo had greater (P < 0.04) undegraded NDF and ADF fractions compared to Pro. The lag prior to DM degradation for Silo treated Pro was less (P < 0.03) than MMR treated with Pro. Rate of degradation of NDF was greater (P < 0.04) for untreated Silo than that treated with XC. The cultivar MMR and sorghum silages treated with either inoculant indicated greater extent and faster rate of DM and fiber degradation.