PS13-22. Screening Maize Inbred Lines for Rumen Fermentation Efficiency and Methane Production Using an In Vitro Model.

Abstract

Genetic variation among maize inbred lines can significantly influence rumen fermentation characteristics, including degradability, gas production, and fermentation end-products. The objective of this study was to screen 40 maize inbred lines for their fermentation characteristics using an in vitro rumen incubation model. Ground, dried biomass collected from the lower portion of the maize inbred lines was used as substrate and incubated with rumen inoculum at 39 °C in triplicate across three independent runs. Dry matter digestibility (DMD) was determined using ANKOM bags incubated for 48 h in a Daisy incubator system. Following initial screening based on total gas production, DMD, and ammonia (NH₃) concentration, the three highest- and three lowest-gas-producing inbred lines, along with a blank control (no subtract added), were selected for detailed analysis of volatile fatty acids (VFA). Gas composition (H2, CH4, and CO2) was analyzed by gas chromatography, and VFA concentrations were determined by HPLC. Data were analyzed using linear mixed-effects models in R, with inbred lines as a fixed effect and incubation (and jar for DMD) as random effects. Tukey’s post hoc test was used for multiple comparisons, and significance was considered at P < 0.05. Total gas production averaged 16.55 mL and differed among inbred lines (P < 0.05), with A208 (22.3 mL) and N523 (21.7 mL) among the highest-producing inbred lines and MQ305 (11.3 mL) and PHJ90 (12.1 mL) among the lowest. CH4 and H2 concentrations averaged 9.62% and 0.44%, respectively, and also differed among inbred lines (P < 0.05). Variety R177 showed significantly higher concentrations for both CH4 (25.9%) and H2 (0.8%), whereas the lowest values were observed for PHH93 (CH4: 2.9%) and PHJ90 (H2: 0.1%). Although the mean NH₃ concentration was 540.2 mg/L, most maize inbred lines reduced NH₃ relative to the blank (P < 0.05). We observed a large variation in the DMD among maize inbred lines, with an overall mean of 44.7%. Significant differences were detected among inbred lines, with A208 showing the highest digestibility (70.7%) and B111 the lowest (16.7%) (P < 0.05). Total VFA production was higher in the high gas-producing subset (∼116 mmol/L) than in the low-producing subset (∼95 mmol/L; P < 0.05). Analysis of individual VFA profiles showed that high gas-producing inbred lines had greater concentrations of propionic (28.6 mmol/L) and butyric acids (14.4 mmol/L) than the blank (85.7 mmol/L) and low-producing inbred lines (95.2 mmol/L; P < 0.05). In contrast, branched-chain VFAs (isovaleric and isobutyric acids) were lower in all maize-containing treatments than in the blank, with isovaleric acid decreasing from 3.81 mmol/L (blank) to 2.7 mmol/L (high gas-producing inbred lines). These results demonstrate that maize inbred lines significantly influence rumen fermentation dynamics in vitro, highlighting the potential to select inbred lines that improve fermentation efficiency while modulating methane emissions.