Forage Mass, Nutritive Value, And In Situ Degradation Of Sorghum Silage Treated With Fibrolytic Enzymes

Sorghum [Sorghum bicolor (L.) Moench.] and sorghum-sudangrass (S. bicolor x S. bicolor drummondii) silage utilization in cattle diets has increased in recent years. The objectives of this study were to compare the forage mass and nutritive value of photoperiod-sensitive (PS) sorghum and hybrid sister lines with or without the BMR trait, and determine if fibrolytic enzymes would improve the rate and extent of in situ disappearance of PS forage sorghum (FS) and PS sorghum-sudagrass (SS) silage varieties with or without the brown midrib (BMR) trait (i.e., FS-PS, FS-PS/BMR, SS-PS, and SS-PS/BMR). This experiment was a 2 x 2 x 2 factorial arrangement whereby the crop was grown, chopped, and ensiled and inoculated with or without (control) the enzyme mixture. Yield was at least 1.6 ton/acre and nutritive value similar to that of similar cultivars. Mini-silo buckets were sealed for 150 days, and dried silage material weighed into duplicate Dacron bags for in situ incubation for 0, 4, 8, 16, 24, 48, or 72 h in three ruminally cannulated Angus steers (679 +/- 52.9 lb body weight [BM]) to determine rate and extent of dry-matter (DM) disappearance. The addition of fibrolytic enzymes had little effect on the nutritive value of ensiled forage. Non-BMR silage had a greater potentially degradable fraction; however, BMR varieties had a greater wash loss and extent of digestion. Based on our results, selecting a sorghum variety with the BMR trait may be more important than using a fibrolytic enzyme to improve silage degradation characteristics.