Effects of Substitution of Corn with Macadamia integrifolia Husk on Rumen Fermentation Characteristics and Microbial...

This study was conducted to measure Macadamia integrifolia husk (MIH) as a feed ingredient for goats using an in vitro rumen fermentation system. Four isonitrogenous and isoenergetic substrates were prepared by using MIH to replace 0, 5%, 10%, or 15% of corn as a dry matter basis, namely MIH0, MIH5, MIH10, and MIH15 groups, respectively. Gas production decreased linearly as corn was replaced by increasing levels of MIH. The DMD decreased linearly at the 24 h and 48 h incubation times as corn was replaced by increasing levels of MIH (p < 0.01). The NDFD decreased linearly at the 6 h, 12 h, 24 h, and 48 h incubation times as corn was replaced by increasing levels of MIH. At 48 h, pH differed extremely significantly (p < 0.001) and followed a quadratic trend (p < 0.05). The MIH0 group had the highest NH₃-N, butyric, and isovaleric acids concentration (p < 0.05); the MIH5 group had the highest MCP, acetic acid, and propionic acid concentration (p < 0.05). Bacteroidota and Pseudomonadota were the dominant phyla in the fermentation fluid at the 48 h incubation timepoint among the four groups. The relative abundance of Kiritimatiellota and Synergistota was highest in the MIH15 group. The relative abundance of Pseudomonadota was highest in the MIH5 group. At the genus level, norank_p_Bacteroidota and Ruminobacter were the dominant genera, and the bacterial community structure differed significantly among the four treatments (p < 0.05). In conclusion, we suggest that the MIH replacing 5% of corn did not affect fermentation, VFA profile, or microbial protein synthesis and it could alter the bacterial communities. Moreover, it is necessary to conduct an in vivo study to investigate the growth performance of goats in a further study.