In Vitro Evaluation of Short-Season Corn Silage Hybrids Grown in Central and Southern Alberta, Canada and Harvested before or after Frost: Nutrient Content, Degradability and Enteric Methane Emission

The objective of this study was to characterize the nutritive value of short-season corn silage (CS) hybrids (rated at ≤ 2600 corn heat units (CHU) for grain maturity), and examine their in vitro rumen fermentation and CH₄ emission (batch culture; 2 runs, 3 replicates/run). Four CS hybrids were grown in 2 years in Central (Lacombe; hybrids: 39F44, 39M26, P7632HR, PS2262RR; 2000-2200 CHU rating) or Southern (Vauxhall; hybrids: P7632HR, P8210HR, P8622AM, P8673AM; 2200-2600 CHU rating) Alberta and harvested before or after slight frost to increase dry matter (DM) concentration. Hybrids grown at each location were selected based on having a CHU rating suitable for the location. Starch content was greater (P < 0.05) for hybrids grown in Southern compared with Central AB (27.8 vs. 22.0% DM) and for hybrids harvested after frost (26.4 vs. 23.4% DM). The NDF content did not differ between locations (mean 53.2%; P > 0.05), but was decreased after frost in Southern hybrids (50.4 vs. 55.0; location × harvest, P = 0.04). Similarly, DMD did not differ between locations (mean 58.7%; P = 0.11), but was increased after frost for Southern hybrids (59.9 vs. 56.5%; location × harvest, P < 0.001). The NDF degradability (NDFD) was greater for Central versus Southern hybrids (39.8 vs 37.5%, P < 0.001), but was increased after frost for Southern hybrids (40.0 vs. 36.0%; location × harvest, P < 0.001). Total VFA concentration in vitro was greater for Central than Southern hybrids (40.2 vs. 37.8 mM), and it increased after frost for Southern hybrids (39.7 vs. 35.9 mM; location × harvest, P = 0.01). The proportion of propionate (mol/100 mol) was greater (P < 0.01) for Southern hybrids (30.7 vs. 29.5) and those harvested after frost (31.0 vs. 29.3). Harvesting before frost tended (location × harvest, P = 0.08) to increase CH₄ (mL/g digested DM) for Central (28.2 vs. 27.0) but not Southern hybrids (mean 25.8). Methane production was inversely correlated with propionate proportion (r=-0.64; P < 0.05). Greater starch content of Southern versus Central hybrids corresponded to lower CH₄ emissions through its impact on propionate. DMD was not affected by location because Southern hybrids had higher starch content but Central hybrids had greater NDFD. Harvesting Southern hybrids after frost increased DMD and thus has the potential to improve animal performance while lowering CH₄ emissions. Although harvesting Central hybrids after frost had limited effects on degradability, it tended to reduce CH₄ emissions.