Tithonia diversifolia Improves In Vitro Rumen Microbial Synthesis of Sheep Diets without Changes in Total Gas and Methane Production

Among the alternatives identified as capable of making livestock farming a more efficient activity and reducing its environmental impact, the use of feeds with high digestibility and the use of non-conventional fodder species can be highlighted. Tithonia diversifolia (Hemsl.) A. Gray (TD) has already gained attention as a feed for ruminants. Nonetheless, there has been little discussion about the impacts of this plant on the rumen dynamics that lead to better animal performance. The aim of this study was to assess how increasing levels of TD could affect ruminal microbial biomass synthesis, degradability, and in vitro gas production (IVGP) of diets. Four diets were evaluated: a control diet (TD0: 400 g kg−1 soybean meal and maize grain, and 600 g kg−1 Tifton 85 hay (Cynodon spp.)) and three increasing levels of TD (TD9: 90, TD27: 270, and TD45: 450 g kg−1–dry matter basis) as a replacement for dietary roughage. A 96 h IVGP assay was carried out and five incubation times (2, 4, 10, 24, and 96 h) were used for degradability determination. Gas produced, methane (CH4), degradability of organic matter (IVDOM), short-chained fatty acid (SCFA) production, partitioning factor (PF), and microbial biomass (MB) were evaluated among treatments. There was no significant effect (p > 0.05) between TD inclusion and IVGP at most incubation times; only at 6 h of incubation did gas production increase linearly with TD inclusion (R2 = 0.19; p < 0.05). TD inclusion had no effects on CH4. IVDOM increased linearly with TD inclusion at 6 and 10 h, with TD45 being more degradable than the control diet at 6 h only. There was a positive linear relationship (R2 = 0.20; p < 0.05) between TD inclusion and PF. TD45 had significantly higher PF values than the control. MB also increased linearly (R2 = 0.30; p < 0.05) with TD inclusion, and all diets with TD had significantly more MB than the control diet. The inclusion of TD at the levels used in this work was revealed to have a positive impact on microbial protein synthesis, which could be related to the higher microbial efficiency of increased substrate quality.