In Vitro Evaluation of Cardoon as a Replacement for Soybean and Sunflower Seeds in Ruminant Diets: Effects on Ruminal Fermentation and Methane Production

Including oilseeds in the diet is a widely studied strategy to reduce CH4 emissions in ruminants, but the effects on ruminal fermentation depend on oilseed composition. This study compared the effects of including three oilseeds (soybean, sunflower and cardoon) differing in fiber content and lignification on in vitro ruminal fermentation and CH4 production of dairy and fattening diets. Oilseeds were included to achieve two dietary lipid levels: low (3.5–4.0%) and high (5.5–6.0%). Diets were incubated in vitro with buffered ruminal fluid from sheep for 17 h. The high lipid level reduced microbial activity only in the fattening diet, particularly after 6 h of incubation, although this effect largely disappeared by 17 h. The most consistent differences among oilseeds were observed in NH3-N concentrations, with soybean yielding lower values than sunflower and cardoon, suggesting reduced protein degradation due to soybean processing. In the fattening diet, cardoon at the low lipid level reduced CH4 production compared with soybean and sunflower (44.9, 50.5 and 52.3 mL/g incubated dry matter) but also reduced total volatile fatty acid production and fermented organic matter, whereas no differences were detected for dairy diets. At equal lipid supply, sunflower and cardoon can replace soybean in dairy diets without negatively affecting ruminal fermentation, whereas cardoon may reduce CH4 production and fermentation in fattening diets at low lipid levels.