Associative effects of diets with different proportions of three types of roughage and Pennisetum giganteum

This experiment was aimed to study the associative effects of diets with different proportions of corn straw, wheat straw, alfalfa hay, and Pennisetum giganteum. The total ratio of concentrate to roughage was set at 40 ꞉ 60, and gas production was determined in vitro. Whereas, the proportion of concentrate, corn straw (wheat straw, or alfalfa ) and P. giganteum were set as follows: 40 ꞉ 60 ꞉ 0, 40 ꞉ 50 ꞉ 10, 40 ꞉ 40 ꞉ 20, 40 ꞉ 30 ꞉ 30, 40 ꞉ 20 ꞉ 40, 40 ꞉ 10 ꞉ 50, and 40 ꞉ 0 ꞉ 60. The gas production in these 21 feed combinations and 5 individual raw materials (concentrate, corn straw, wheat straw, alfalfa hay, P. giganteum) were recorded at 2, 4, 6, 8, 12, 24, 36, and 48 h. After incubation, the incubation fluid was used to determine pH, ammonia nitrogen, and total volatile fatty acid; while the residue was used to determine dry matter digestibility. The single-factor AE indexes and multiple-factor AE indexes were then calculated. The results showed that after fermentation for 48 h, the gas production was ranked: concentrate > alfalfa hay > wheat straw > P. giganteum > corn straw. From the different combinations, the average gas production of concentrate + alfalfa hay + P. giganteum > concentrate + wheat straw + P. giganteum > concentrate + corn straw + P. giganteum at each time point. For the combination of concentrate + alfalfa hay + P. giganteum, the gas production in A6P0, A5P1, A4P2 groups was significantly higher than that in A3P3, A1P5, and A0P6 groups (P < 0.05) at 12 h of fermentation. The gas production increased with a higher proportion of alfalfa and a lower proportion of P. giganteum. For the concentrate + wheat straw + P. giganteum combination, the gas production in W3P3, W2P4, W1P5, and W0P6 groups was significantly higher than that in W6P0, W5P1, and W4P2 (40 ꞉ 40 ꞉ 20) (P < 0.05) at 12 h of fermentation. The gas production increased with a lower proportion of wheat straw and a higher proportion of P. giganteum. These results demonstrate that in the concentrate + corn straw + P. giganteum combination, the AE was best at a ratio of 40 ꞉ 20 ꞉ 40; while in the concentrate + wheat straw + P. giganteum combinations, the AE was best at a ratio of 40 ꞉ 20 ꞉ 40; and in the concentrate + alfalfa hay + P. giganteum combination, AE was better when the ratio was 40 ꞉ 50 ꞉ 10.