PS3-16. Ruminal Degradability Kinetics of a Highly Processed Cereal Grain Substrate Within Beef Steers Offered Live Yeast on Finisher or Grower Diets.

Abstract A highly processed cereal grain (gelatinized matrix) substrate ruminal degradability kinetics on cattle consuming grower or finisher diets with or without live yeast were evaluated. Eight ruminally cannulated beef steers were used in a duplicated 4 × 4 Latin Square design following a 2 × 2 factorial arrangement of treatments: A) presence of live yeast (Saccharomyces cerevisiae [CNCM I-1077], at 1 × 1010 CFU/animal-daily); and B) diet type (steam-flaked corn-based grower or finisher diets [ad libitum intake]). Live yeast was delivered via gel capsules (0.25 g, as-is) twice daily through the ruminal cannula. Pre-dehydrated (55ºC for 72 h) substrate (steam-flaked corn, bulk density = 360 g/L) was ground (2 mm) and placed into 10 × 20 cm (28 µm) nylon bags (8g, as-is). Substrate bags were incubated within the rumen by placing it at the ruminal ventral sac within a nylon mesh (with weights) and removed at 0, 2, 4, 8, 12, 20, 32, 48, 64, 72, and 96 h. Samples were removed, rinsed, and dehydrated for 72 h at 55ºC. Residues were composited by period, steer, and incubation time, corrected for residual moisture, and were used to fit a first-order kinetics model using the NLIN procedure of SAS. The GLIMMIX procedure of SAS was used with animals as the experimental unit; the fixed effects of diet, treatment, and interaction; random effects of animal within square and period. Additional substrate was used within in situ bags but residue was not enough for extra detailing within some fiber fractions assessment. Diet × Yeast interaction was not observed (P ≥ 0.22), while a tendency (P = 0.09) was detected (F-test) for ADF fraction lag time, but after Tukey's adjustment the tendency was no longer present (P = 0.21). Regardless of diet type, live yeast decreased (P = 0.02) the substrate NDF undegradable fraction and increased the NDF effective degradability at 4, 5, and 6% rate of passage (P ≤ 0.01), while other degradability fractions were not affected (P ≥ 0.14). Regardless of live yeast inclusion, the steam-flaked corn-based grower diets decreased (P < 0.01) the substrate undegradable fraction, increased the potentially degradable fraction (P < 0.01), and increased (P < 0.01) the effective degradability at 4, 5, and 6% rate of passage of both dry matter and organic matter fractions. The substrate NDF undegradable fraction was reduced (P = 0.03) on grower diets, while within the same diet type, the NDF potentially degradable fraction tended to increase (P = 0.06). Live yeast improved the fiber degradation profile of a highly processed cereal grain (steam-flaked corn) substrate regardless of whether it is on a grower or a finisher diet. Grower diets improved the substrate ruminal overall degradability compared to finisher diets.