Abstract

Improving the quality of ruminant diets can be an effective strategy for mitigating enteric methane (CH4) production. The aim of this study was to assess the effects of increasing concentrations of glycerol in concentrate diets supplemented with linseed on CH4 production and rumen fermentation parameters. Experimental diets were: Control (61%:25%:14% corn, mixed hay, and soy); positive control (51%:25%:9%:15% corn, mixed hay, soy, and linseed); Gly 5% (46%:25%:9%:15:5% corn, mixed hay, soy, linseed, and glycerol); and Gly 10% (40%:25%:10%:15%:10% corn, mixed hay, soy, linseed, and glycerol). Diets were incubated in a completely randomized design in a Rusitec apparatus (10 d adaptation, 5 d sampling). Differences were analyzed using Tukey’s test, contrasts, and principal component analysis. Results showed that linseed supplementation reduced CH4 (P ≤ 0.004) and ammonia N (NH3-N; P = 0.012) production. However, while the use of glycerol increases CH4 production (P ≤ 0.002) in linseed-supplemented diets, it simultaneously reduces NH3-N production (P = 0.004). Linseed supplementation decreased the degradability of DM, crude protein, and non-fibrous carbohydrates but increased ether extract (EE) degradability (P ≤ 0.013). Similarly, glycerol enhanced EE degradability and increases DM degradability in linseed-supplemented diets (P ≤ 0.006). Both linseed and glycerol shift the fermentation profile by decreasing acetate proportions (P ≤ 0.002) and increasing propionate proportions (P < 0.001), which reduces the acetate-to-propionate (A:P) ratio (P < 0.001). Overall, the combination of linseed and glycerol in concentrate diets reduces NH3-N production without lowering CH4 emissions and may even increase them. This combination also decreases the A:P ratio and enhances EE and DM degradability in linseed-added diets