Hydroponic fodders as alternative feeds for ruminants to reduce ruminal methane emissions: An in vitro study

Malate, a precursor in the ruminal propionate production pathway, competes with methanogenesis for metabolic hydrogen, offering a way to reduce ruminal methane (CH₄) production in ruminants. However, cost considerations hinder widespread use of malate in ruminant diets. An alternative approach involves use of transient malate levels generated during seed germination via the glyoxylate cycle. This study investigated the methane-mitigating potential of malate-containing hydroponic fodder. Fodder samples with peak malate concentrations from alfalfa, forage pea, Italian ryegrass, rye, soybean, triticale, and wheat during germination were subjected to in vitro rumen fermentation using the Hohenheim gas test. The basal diet of in vitro fermentation comprised 40% grass silage, 40% maize silage, 15% hay, and 5% concentrate on a DM basis, with nutritional characteristics including 42.1% NDF, 25.0% ADF, 14.0% starch, 12.7% CP, and 3.5% ether extract, on a DM basis. Experimental treatments were fodder inclusion involving replacing 20% of the basal diet (20R) and, additionally, 100% replacement of the silages with alfalfa d 10 and rye d 9 (SR), the 2 high-malate fodders. Reductions in CH₄ production were observed with soybean (20R, 6.7% reduction), alfalfa (20R, 6.6% reduction), and increased with rye (20R, 6.3% increase). In the setup replacing silages with high-malate fodders (SR), alfalfa decreased CH₄ production (17.7%) but increased ammonia (174%), whereas rye increased CH₄ production (35.8%). Organic matter digestibility increased with SR rye (12.6%). Marginal effects of dietary variables were analyzed in a generalized additive model. A negative relationship between dietary malate content and CH₄ production was observed, whereas dietary NDF and starch content were positively correlated with CH₄ production. In conclusion, malate within the hydroponic fodder could potentially reduce CH₄ emissions in ruminants. However, achieving sufficient efficacy requires high malate content. Additionally, use of hydroponic fodder may increase the risk of nitrogen emissions. Animal studies are required for further investigation.