Evaluation of a mixture of crude glycerol and molasses as an energy supplement for beef cattle consuming bermudagrass hay

Abstract

objectives of our study are 1) to determine the effects of different levels of supplementation with a 50:50 mixture of molasses:crude glycerol on bermudagrass hay intake and digestibility of nutrients in the total tract, and 2) to determine the effects of different levels of supplementation with a 50:50 mixture of molasses:crude glycerol on ruminal in situ digestibility of the fiber fraction and in vitro ruminal fermentation parameters. Two ruminally cannulated steers (approx. 1100 lb) will be used as rumen fluid donors for the in vitro incubations. The steers will be fed a diet comprised of 100% Tifton 85 bermudagrass hay (same hay used in Phase 1) for at least 14 d prior to the collection of ruminal fluid to perform the in vitro incubations. In vitro incubations will be performed in three separate days (replicates) using a substrate comprised of the same 4 diets tested in Phase 1 and considering the hay intake observed. The substrate will be mixed with the inoculum (3:1 mixture of McDougall's buffer:ruminal fluid) and duplicate bottles per treatment will be incubated in each day replicate.The in vitro incubations will be conducted in 250-mL bottles and gas production kinetics will be recorded using the Ankom Gas Monitoring System (Ankom Technologies, Fairport, NY). Bottles containing 1.4 g of substrate and 100 mL of inoculum will be incubated for 24 h at 39°C and volatile fatty acid concentrations will be measured at the end of the incubation period along with NH3-N concentrations, and final pH. A measurement of in vitro dry matter digestibility will be performed by incubating a separate set of duplicate 100-mL scintillation flasks for 24 h at 39°C in each of the replicate days. These flasks will contain 0.7 g of substrate and will be inoculated with 50 mL of a 3:1 McDougall's buffer:ruminal fluid mixture. This phase will be analyzed as a completely randomized design using the MIXED Procedure of SAS (SAS Institute Inc., Cary, NC). Each flask/bottle will be considered the experimental unit (average of 2 flasks/bottles in each incubation day). The model will include the fixed effects of treatment and the random effect of incubation day. In addition, orthogonal polynomial contrast will be conducted to determine the effects of supplementation level of ruminal fermentation parameters. Significance will be determined at P d 0.05 and tendencies will be considered when 0.10 > P > 0.05. (AU)