In vitro gas production and rumen fermentation for diets containing increasing levels of Panicum maximum cv. Mombasa with or without spirulina.

This study was designed to evaluate the effect of substituting alfalfa hay with graded levels panicum maximum without or with graded levels of spirulina supplementation on rumen fermentation and nutrient degradability. The evaluation was achieved through an in vitro study, rumen fluid was obtained from adult sheep aged 2 years (fed clover hay), immediately after slaughter. Experimental diets were formulated as isonitrogenous and isocaloric and contained 40% forage. Forage composition was altered by substituting alfalfa hay with graded levels of panicum maximum hay, so that treatment diets contained 0, 25, 50, 75, and 100% of the forage from panicum maximum for treatments R1, R2, R3, R4, and R5, respectively. Additionally, each treatment was further supplemented with graded levels of spirulina at the following rates: 0, 0.5, 1.5, 2, 2.5, and 3 mg/g. Results indicated that gas production after 24 h per g DM, OM and DDM has a positive linear relationship with spirulina supplementation level (R² = 0.80, 0.83, and 0.93, respectively). The gas production increased by increasing the level of Spirulina. However negative linear relationships were recorded between gas production per g DM, OM, DDM and alfalfa substitution level (R² = 0.97, 0.95, and 0.96, respectively) which the gas production decreased as the substitution level increased. In vitro degradability of dry and organic matter was decreased by the increment of Panicum maximum and Spirulina supplementation levels and vice versa, until 2 mg/g of Spirulina (p < .0001). The addition of Spirulina significantly (p < .0001) increased total volatile fatty acids (TVFA) and NH₃ concentration, until 2mg/g, while the addition of Panicum maximum hay significantly increased NH₃ concentration, until it reached at (R4). In conclusion, the substitution of alfalfa hay with graded levels of Panicum maximum hay may be reduce nutrients degradability and gas production while supplementing diets with graded level of spirulina improve degradability and ruminal fermentation parameters.