In Situ Degradation Characteristics of Sorghum Silage Treated with Fibrolytic Enzymes
Sorghum (Sorghum bicolor L.) silage utilization in beef and dairy cattle diets has increased in recent years due to the increased water efficiency and acceptable feeding values when compared to corn silage. The objective of this study was to determine if fibrolytic enzymes would improve the rate and extent of in situ disappearance of photoperiod sensitive sorghum and hybrid silage varieties with or without the brown midrib (BMR) trait: forage sorghum (FS), BMR forage sorghum (FS-BMR), sorghum-sudangrass (SS), and BMR sorghum-sudangrass (SS-BMR). The experiment was a 4 × 2 factorial design with two replicated periods. Each sorghum silage variety (n=4) was grown, harvested, chopped, and treated with water (control) or a fibrolytic enzyme (50:50 mixture of Cellulase Plus and Xylanase Plus) prior to the ensiling process. Mini-silo buckets were sealed, maintained at 23ºC for 150 d, dried, subsampled, ground to 4 mm, and weighed into duplicate Dacron bags for the in situ trial. An additional silage subsample was taken and stored at -20ºC for subsequent pH determination. Three ruminally cannulated Angus steers (308 ± 24 kg) had ad libitum access to sorghum-sudangrass hay (‘Haygrazer’), mineral, and water for 14 d prior to incubation periods. Sorghum silage samples were incubated in situ for 0, 4, 8, 16, 24, 48, or 72 h to determine rate and extent of DM disappearance. Sorghum silage yields were low due to drought. SS yielded the most (P < 0.01; 5.3 Mg of DM/ha) compared to SS-BMR (3.8 Mg of DM/ha), FS (3.8 Mg of DM/ha), and FS-BMR (3.7 Mg of DM/ha). All silage reached a pH between 3.1 and 3.5, suggesting that proper ensiling did occur. There were no interactions between treatment and forage variety for DM (P ≥ 0.21) in the in situ trial. The lag and undegraded residue fraction was not different between varieties (P > 0.81). Non-BMR silage had a greater potentially degradable fraction (P < 0.01); however, BMR varieties had a greater wash loss (A; P < 0.01) and extent of digestion (ERD; P < 0.01). Enzyme treated forage also had a greater A fraction (P = 0.03) and ERD (P = 0.03), indicating that fibrolytic enzymes can improve silage ruminal degradation. Selecting a sorghum variety containing the BMR trait or using a fibrolytic enzyme can improve silage degradation characteristics.
sorghum silage, brown midrib, fibrolytic enzymes