The Effects of Added Cellulases and Pectinases on Ruminal Fermentation Parameters and Bacterial Communities in Goats Supplemented with Macadamia Integrifolia Husks: An In Vitro Study.

Macadamia integrifolia husk has great potential for use as a feedstuff in ruminants. However, little information regarding its effects on ruminal fermentation traits is available at present. Hence, this in vitro study aims to investigate the effects of Macadamia integrifolia husk as a substrate, supplemented with enzymes at different levels (0 g/kg cellulases + pectinases, CON; 0.5 cellulases + 0.5 g/kg pectinases, TRE1; 1.0 g/kg cellulases + 0.5 g/kg pectinases, TRE2; 1.5 cellulases + 0.5 g/kg pectinases, TRE3), on gas production, fermentation traits, and bacterial communities in goats. The results demonstrate that gas production was increased in TRE1 and TRE3 groups compared to the CON group at 6, 9, 12, 24, and 48 h (p < 0.05); DMD was the highest in the TRE3 group and the lowest in the CON group at 6, 12, 24, and 48 h (p < 0.05); and NDFD was the highest in the TRE1 group and the lowest in the CON group at 6 h, then the highest in the TRE3 group and the lowest in the CON group at 12, 24, and 48 h (p < 0.05). The concentrations of MCP, TVFAs, acetate, and propionate were the highest in the TRE3 group and the lowest in the CON group (p< 0.05). The abundance of Bacillota was the highest in the TRE1 group and the lowest in the TRE2 group (p < 0.05), whereas that of Synergistota and Actinomycetota was the lowest in the CON group and the highest in the TRE2 group (p < 0.05). Acidobacteriota was the most abundant in the TRE3 group and the least abundant in the TRE1 group (p < 0.05). The most abundant genus was norank_p_Bacteroidota, comprising approximately 29.3%, 30.6%, 30.4%, and 31.7% of the total bacteria in the CON, TRE1, TRE2, and TRE3 groups, respectively; this was followed by Succiniclasticum, comprising approximately 6.3%, 5.8%, 6.1%, and 7.0% of the total bacteria in the CON, TRE1, TRE2, and TRE3 groups, respectively. This study provides new insights regarding the use of Macadamia integrifolia husk as a feedstuff in goats; in particular, supplementation with cellulases and pectinases could effectively improve its utilization. The results suggest that the optimal supplementary levels of cellulases and pectinases are 1.5 g/kg and 0.5 g/kg, respectively.