Effects of Lipid Supply Form (Whole Seed vs. Free Oil) on In Vitro Ruminal Fermentation and Methane Production of Diets for Dairy and Fattening Sheep

Abstract

Enteric methane (CH4) emissions from ruminants contribute substantially to greenhouse gas production. Dietary lipid supplementation is a mitigation strategy, but its effects are variable. We evaluated the effects of lipid source (soybean, sunflower, and cardoon) and lipid supply form (whole oilseed vs. free oil) on in vitro ruminal fermentation and CH4 production of diets representative of those fed to dairy ewes and fattening lambs. For each oilseed, treatments included a control (no added lipids) and either the whole seeds or the extracted free oils at final lipid concentrations of 5.0–5.5 and 6.0–6.5% dry matter for dairy and fattening diets, respectively. Diets were incubated for 17 h with ruminal fluid from sheep fed either dairy or fattening diets. No interactions between diet type and lipid supply form were detected for any oilseed, and lipid supply did not influence ruminal fermentation. Lipid supply form had no effects on methane-related parameters in soybean diets. Compared with the whole seed, the free oil reduced the CH4/total short-chain fatty acids ratio in both sunflower and cardoon diets, and decreased CH4 production and CH4 proportion in total gas in cardoon diets. The effects of lipid supply form depended on the oilseed, with cardoon-free oil showing the greatest potential for CH4 mitigation. These findings highlight the potential of selected free oils as candidates for methane mitigation and the usefulness of in vitro methane production as a screening tool to identify lipid sources with potential for reducing methane emissions, which should subsequently be evaluated in vivo.