Effects of isopropyl ester of hydroxy analog of methionine (HMBi) on in vitro rumen fermentation, enzymatic activity and nutrient digestibility

The study aimed to explore in vitro ruminal effects of isopropyl ester of hydroxy analog of methionine (HMBi) to enhance understanding of rumen degradable portion of it. In Experiment 1, HMBi (KMFD, KESSENT® MF Dry, Kemin Animal Nutrition and Health, Belgium) was added to a basal feed (10% as fed) and incubated for 24 h in Hohenheimer Futterwerttest (HFT) and Daisy incubator (3 runs × 6 replicates). Basal feed was incubated as a control (CON). In Experi- ment 2, an in vitro 24-h rumen incubation was performed followed by a radial enzyme diffusion (RED) test of KMFD to observe the enzymatic activities (EA) of amylase (Amy), cellulase (Cel), and xylanase (Xyl) over time (n = 60, expressed as area of hydrolysis). A mixed model was used with REML (JMP 16.1, SAS) with fixed effects of treatment and random effects of each run of incubators. In RED, time was assigned as a fixed effect and each Petri was considered a random effect. After 24 h of incubation in HFT, KMFD did not affect pH, nor the molar level of acetic, isobutyric, isovaleric, valeric, caproic, and lactic acids, as well as total gas and methane production (mL/g DM). Molar concentrations of ammonia-N (20.3 vs. 17.4 ± 1.2), butyric acid (8.2 vs. 7.2 ± 1.0), and Ace:Pro ratio (5.2 vs. 4.8 ± 0.1) decreased with KMFD supplementa- tion compared with CON, whereas propionic acid increased (P < 0.05). In addition, KMFD improved in vitro (%) total true digestibility and nutrient digestibility compared with CON (P < 0.05). Percentages of IVTD, IVTDDM, IVTDNDF, and IVTDOM were 71.6 versus 74.2 ± 1.5%; 68.7 versus 71.6 ± 1.6%; 19.7 versus 27.1 ± 4.2%, and 59.6 versus 63.4 ± 2.3% for KMFD versus CON, respectively. Compared with time-zero, Xyl EA linearly decreased (1.9 vs. 1.4 ± 0.1), whereas Cel EA increased (3.1 vs. 4.1 ± 0.1) after 2 h (P < 0.05) over time. The initial Amy EA was maintained by 12 h (P > 0.05) and increased at 24 h (3.3 vs. 4.0 ± 0.2, P < 0.05). In conclusion, the observed reduction in the rumen-free ammonia-N and alterations in some rumen fermenta- tion patterns and EA with KMFD supplementation suggest an effect of a degradable portion of its HMBi concentration on nutrient utilization under in vitro rumen conditions.