Methane production, fermentation characteristics, and microbial profiles in the rumen of tropical cattle fed tea seed saponin supplementation

Belmont Red Composite rumen-cannulated steers (n=8, 364±8.4kg liveweight, LW; least squares means±s.e.m.) were used to assess effects of feeding tea seed (Camellia sinensis L.) saponin (TSS) supplementation on performance, methanogenesis, fermentation pattern and rumen microbial communities. The expectation was to use TSS to potentially modulate the rumen microbial population and decrease enteric methane (CH4) production. The steers were fed twice a day with a basal diet (BD) that contained a mixture of 0.15 Rhodes grass (Chloris gayana) hay plus 0.85 of a commercial concentrate before CH4 emissions were measured in open-circuit respiratory chambers for 48h. Steers were then adapted progressively to doses of 20 and 30g/day of TSS for 10 and 6 days, respectively before new CH4 measurements were recorded. Final placement in chambers was conducted after 13days of TSS removal (BDP). Rumen fluid samples from each steer were collected for the treatments BD, BD+20g TSS, BD+30g TSS and BDP. Growth performance and CH4 emissions were not affected by the addition of TSS, but compared to the BD and TSS diets, daily CH4 emissions (g) and yield (gCH4/kg DMI) were lower (P<0.05) by 18 and 22%, respectively, after TSS treatment. Concentrations of total volatile fatty acids, acetate and propionate were not affected by TSS treatment, as were total rumen bacteria and methanogens numbers. Relative to the BD and BDP, butyrate concentration was higher (P<0.05) in TSS treated animals, resulting in a reduced ratio of acetate to butyric acid (P<0.05). In comparison with BD control, the relative abundance of Fibrobacter succinogenes increased by 2 fold (P<0.001) in the other three dietary groups. However, compared to the BD and BD+20g of TSS, the abundance of R. albus increased by 100 fold (P<0.01) in the BD+30g of TSS and BDP diets, while the abundance of R. flavefaciens was 100 fold lower in TSS supplemented and BDP groups than in BD control group (P<0.001). Thermoplasmatales-related RCC archaea and protozoa counts increased linearly with 20 and 30g of TSS addition, but returned to BD control levels after the TSS supplement was withdrawn. It was concluded that TSS supplementation changed rumen microbial community in cattle, but was not inhibitory to methane production, which was inconsistent with published in vitro results and small ruminant trials where TSS caused a dose-dependent reduction in CH4 emissions.