EFFECT OF VARIETY OF SORGHUM GRAIN ON DIGESTION AND AVAILABILITY OF DRY-MATTER AND STARCH INVITRO

Studies of ruminal dry matter disappearance in vitro (IVDMD) and gas production in vitro (GP) were conducted to evaluate utilization characteristics of four divergent sorghum grain varieties, representing three pureline varieties and a commercial millrun sorghum. Pureline varieties included: 1133, a waxy endosperm, high tannin, bird resistant (BR) sorghum (Waxy-BR); Darset, a normal endosperm or non-waxy BR type (Normal-BR); Dwarf Redlan, a waxy endosperm, low tannin, non-BR type (Waxy). The millrun sorghum, representative of much commercial sorghum, was a normal endosperm, non-BR type (Normal). Ruminal fluid was obtained from animals fed a BR or a non-BR sorghum grain diet to evaluate the potential interaction between dietary condensed tannin level and IVDMD of sorghum grain varieties. This interaction was not significant (P > 0.20), though IVDMD tended to be lower for all varieties when incubated in BR vs. non-BR ruminal fluid (36.4 vs. 40.9%). IVDMD was greater (P < 0.01) for Waxy-BR (35.4%) than for Normal-BR (30.9%), but lower than for Waxy (44.3%); Normal-BR was also lower (P < 0.01) than Normal (44.0%). Non-BR varieties produced more (P < 0.001) CO2 at 12 h (103.2 ml g-1 grain starch) than BR types (74.9 ml), and waxy endosperm varieties yielded more (P < 0.001) CO2 (97.7 ml) than normal endosperm varieties (80.5 ml). When a single pool kinetic model was fitted iteratively to GP data, starch digestion occurred at a greater rate (P < 0.05) for Waxy compared with Waxy-BR or Normal. Waxy endosperm increased starch availability and moderated the negative effect of tannin. © 1990.