Potential of Agroindustrial By-Products to Modulate Ruminal Fermentation and Reduce Methane Production: In Vitro Studies

SIMPLE SUMMARY: Exhausted olive cake, tomato pomace and wine lees are agroindustrial by-products extensively produced in the Mediterranean area that could be used in ruminant feeding, but the information on their optimal inclusion level in ruminant diets is scarce. Exhausted olive cake and tomato pomace are fibrous by-products and therefore are more adequate for ruminant feeding, whereas wine lees can have high protein content. The objective of this study was to evaluate the effect of including increasing amounts of these by-products in diets for fattening ruminants on in vitro ruminal fermentation and methane production. We analysed the in vitro fermentation of diets including 0, 6, 12 and 18% of these by-products. Including up to 18% of a 1:1 mixture of exhausted olive cake and tomato pomace had no negative effect on in vitro ruminal fermentation, but decreased ammonia concentrations, probably due to the low crude protein digestibility of both by-products. In contrast, high amounts of wine lees (12 and 18%) had negative effects on in vitro ruminal fermentation, and consequently they could only be included up to 6% to avoid negative effects. The absence of effects of any tested by-product on methane production indicates that they lack antimethanogenic compounds. ABSTRACT: The effects of including wine lees (WL), exhausted olive cake (EOC) and a 1:1 mixture of EOC and tomato pomace (EOCTP) in diets for fattening ruminants on in vitro fermentation parameters and CH(4) production were analysed. Ten diets were studied, containing either none of the tested by-products (control), or 6.0, 12.0 or 18.0% of WL, EOC and ECOTP formulated to have similar protein and fiber content. Diets were incubated in vitro with sheep ruminal fluid to measure gas production kinetics and fermentation parameters. Increasing the level of WL, EOC and EOCTP decreased linearly (p ≤ 0.009) the potential gas production, but other gas production parameters were unaffected (p > 0.05), excepting that EOCTP increased the gas production rate. No differences (p ≥ 0.0.05) among diets were observed in total volatile fatty acid (VFA) production at 24 h of incubation for EOC and EOCTP, but NH(3)-N concentration decreased (p ≤ 0.003). In contrast, WL at 12.0 and 18.0% decreased (p < 0.05) total VFA production and increased the acetate/propionate ratio (p < 0.05). None of the by-products had an effect on CH(4) production (p ≥ 0.0.05). Results indicate that EOC and EOCTP could be included up to 18.0% in fattening diets, but lower levels of WL are recommended.