Effect of Two Selected Levels of Padina gymnospora Biowaste and Enteric Methane Emission, Nutrient Digestibility, and Rumen Metagenome in Growing Sheep

A study was conducted on growing sheep to investigate the effect of two selected levels of biowaste of Padina gymnospora on feed intake, digestibility, daily enteric methane (CH4) emission, growth performance, and rumen metagenome. We randomly divided the 18 growing male sheep into three groups of six animals each. The animals were fed on a basal diet comprising finger millet straw (Eleusine coracana) and a concentrate mixture in a 35:65 ratio. The sheep in the control group (C) were offered a concentrate mixture without waste, whereas the wheat bran in the concentrate mixture in test group I (A2) and test group II (A5) was replaced (w/w) with the biowaste of Padina gymnospora at a level of 3.07 and 7.69%, respectively. The biowaste of Padina gymnospora at the above levels in concentrate constituted 2 and 5% of the diet. A significant decrease of 28.4% in daily enteric CH4 emission (g/d) was reported in the A5 group, whereas the difference in daily enteric CH4 emission between the C and A2 & A2 and A5 groups did not prove significant. The inclusion of Padina gymnospora biowaste did not affect the nutrient intake and digestibility among the groups. The inclusion of Padina gymnospora biowaste in the A5 group resulted in a significant reduction (p = 0.0012) in daily CH4 emissions compared with group C; however, no significant differences were observed in daily CH4 emissions between groups C–A2 (p = 0.0793) and A2–A5 (p = 0.3269). Likewise, the adjustment of data to CH4 emissions per 100 g of organic matter intake indicated a substantial decrease in the A5 group relative to C. The energy loss in CH4 as a percentage of GE relative to group C decreased significantly (−23.4%) in the A5 group; however, this reduction was not associated with an increase in productivity, as almost similar average daily gain (p = 0.827) was observed in the groups. The replacement of wheat bran with the biowaste of Padina gymnospora significantly decreased the numbers of total protozoa and holotrichs in the A5 group. Irrespective of the group, the Bacteroidota was the single largest phylum in the rumen metagenome, representing >60% of the microbiota. However, the abundance of Bacteroidota was similar among the groups. The methanogenic phyla Euryarchaeota was the 5th most abundant; however, it constituted only 3.14% of the metagenome. The abundance of Desulfovibrio was significantly higher in the A5 group as compared with the control. In conclusion, the significant increase in the abundance of sulfate-reducing bacteria and reduction in protozoal numbers led to a significant reduction in CH4 emissions with the incorporation of biowaste of Padina gymnospora at a 5% level of the diet.