Fermentation Patterns, Methane Production and Microbial Population under In Vitro Conditions from Two Unconventional Feed Resources Incorporated in Ruminant Diets

SIMPLE SUMMARY: The production of greenhouse gases (GHG) from livestock and its impact on climate change are a major concern worldwide. It has been reported that enteric methane is the most important GHG emitted in ruminant production systems at a farm scale, accounting for approximately 50 to 60%. Many attempts have been made to modify fermentation ruminal and decrease methane production. It has recently been shown some plants, leaves, fruits, and roots reduce methane production in the rumen. Therefore, this study was conducted to investigate the inclusion of Leucaena leucocephala leaves (LLL) and prickly pear (PP) (Opuntia ficus-indica) in ruminant diets, on ruminal fermentation patterns, methane production, and microbial population under in vitro conditions. The results showed that the inclusion of Leucaena leucocephala in the diet decreased the concentrations of methane (CH4) and also decreased the constant rate of degradation of dry matter, ammoniacal nitrogen (NH3-N), and microbial biomass synthesis (MBS). In addition, Opuntia ficus-indica recorded higher potential gas production and higher dry matter intake compared to Leucaena leucocephala. ABSTRACT: In this study, four experimental treatments were evaluated: (T1) alfalfa hay + concentrate, (50:50%, DM); (T2) alfalfa hay + Leucaena leucocephala + concentrate, (30:20:50%, DM); (T3) alfalfa hay + prickly pear + concentrate, (30:20:50%, DM); and (T4) alfalfa hay + Leucaena leucocephala + prickly pear + concentrate, (30:10:10:50%, DM). NH3-N concentrations in T2 and T4 decreased when replaced with alfalfa hay in 20 and 10%, respectively. Treatments did not affect the concentration of total volatile fatty acids (TVFA) between T3 and T4 (p > 0.05), while the concentrations among T1 and T2 were different (p < 0.05). T2 showed a reduction of 25.5% in the methane production when compared to T1 (p < 0.05). The lowest concentrations of protozoa were observed in T2 and T4, which contained Leucaena leucocephala (T2) and Leucaena leucocephala + prickly pear (T4) (p < 0.05). The highest concentration of total methanogens was recorded in T1 and was different in T2, T3, and T4 (p < 0.05). Leucaena leucocephala, at an inclusion percentage of 20%, decreased the methane when compared to T1, whereas prickly pear increased methane production in relation to T1.