Lupin Seed Supplementation as a Functional Feed Additive: In Vitro Ruminal Gas, Methane and Carbon Dioxide Production, Fermentation Kinetics, and Nutrient Degradability.

The inevitable enteric gas emission from ruminants is considered a modern-day problem from an environmental perspective. Addressing this problem requires nutritional approaches such as the use of phytogenic additives in ruminant diets. In this regard, lupin seed (LS) can be a useful additive due to its phytochemical constituents. Therefore, this study investigated the effects of lupin ( Lupinus angustifolius ) seed supplementation as a functional and sustainable feed additive in sheep diet (50:50 concentrate-to-forage ratio) on in vitro gas production (GP; mL/g DM), methane (CH 4 ; mL/g DM) and carbon dioxide (CO 2 ; mL/g DM) emissions, fermentation parameters, and nutrient degradability (g/kg DM incubated). Gas production and CH 4 were measured per gram of incubated dry matter (DM), degradable DM ( d DM), degradable neutral detergent fiber ( d NDF), and degradable acid detergent fiber ( d ADF). Lupin seeds were included at 0 (control), 0.5, 1.0, 1.5, and 2% of the diet. The seeds contained 3.27% essential oils (DM basis), with eucalyptol as the main phytochemical. The highest GP per gram of DM and d DM was observed ( p < 0.01) with 2.0% LS supplementation level. While 1.0% LS had the highest GP per gram of d NDF, 0.5% lupin diet had the highest GP per gram of d ADF. Asymptotic GP and CH 4 emissions linearly and quadratically increased ( p < 0.01) with increasing LS level, while lag time decreased. Despite increased CH 4 production, the proportion of CH 4 in total biogas was lower ( p = 0.008) for LS treatments than the control, with the 0.5% LS showing the lowest CH 4 proportion. Production of CO 2 increased with lupin seed treatments, with 0.5% LS producing the highest proportion ( p = 0.027). Degradability of DM, NDF, and ADF was greater ( p < 0.01) for the high LS supplementation level, while 0.5% supplementation level decreased ADF degradability. Total short-chain fatty acids, acetic acid, and propionic acid increased ( p < 0.05) with LS supplementation level, leading to a reduced acetate:propionate ratio. Rumen pH decreased ( p = 0.036) with LS supplementation, while ammonia-N decreased ( p = 0.045) and estimated metabolizable energy increased ( p < 0.001) linearly. Calculated microbial protein synthesis ( p = 0.005) and gas yield ( p = 0.047) increased with LS supplementation level. LS supplementation at 2.0% of diet (DM basis) increased GP and CH 4 emission (mL/g DM) and enhanced nutrient degradability, suggesting its potential use as a functional feed additive for ruminants when supplemented at a 2.0% level into diet.