Influence of mangosteen peel powder as a source of plant secondary compounds on rumen microorganisms, volatile fatty acids, methane and microbial protein synthesis in swamp buffaloes

The objective of this experiment was to evaluate the effect of mangosteen peel powder (MSP) on rumen fermentation, nutrient digestibility and microbial population in swamp buffaloes (Bubalus bubalis) fed on a rice straw based diet. MSP is a fruit peel that contains plant secondary compounds (condensed tannins and saponins). Eight, rumen-fistulated 4-year old, male swamp buffaloes with 350±4 kg live weight were randomly assigned to receive two dietary treatments (T1=non-supplementation of MSP and T2=supplementation of MSP at 100 g/(head×day)) according to a t-test design. All animals were fed concentrate mixtures at 0.5% of body weight and rice straw was fed ad libitum for 37 days with the first 30 days for feed adaptation and voluntary feed intake measurement, while the last 7 days were for samples collection. The results revealed that there was no difference between treatments on dry matter intake and nutrient digestibility by MSP supplementation (P>0.05). Furthermore, MSP supplementation did not influence ruminal pH, temperature, ammonia nitrogen and blood urea nitrogen. Interestingly, propionic acid (C3) production was significantly increased by MSP supplementation (P<0.05) while total volatile fatty acids, acetic acid (C2) and butyric acid were similar between treatments. Moreover, C2:C3 ratio was reduced by MSP supplementation. In addition, estimated rumen methane was significantly reduced by MSP supplementation (P<0.05). Application of quantitative PCR to quantify cellulolytic bacteria (16S rRNA) targets revealed that MSP supplementation did not change population of Fibrobacter succinogenes and Ruminococcus albus (P>0.05) while total bacteria population were significantly increased by MSP supplementation. The Ruminococcus flavefaciens and methanogens population were significantly decreased as MSP were supplemented (P<0.05). Nitrogen intake, excretion (fecal and urine) and balance (absorption and retention) were similar between treatments whilst microbial nitrogen supply and efficiency of microbial protein synthesis were increased by MSP supplementation. In conclusion, supplementation of MSP as a source of plant secondary compounds exhibited no negative effect on feed intake, nutrient digestibility, ruminal fermentation characteristics, nutrient utilization and microbial protein synthesis. But rather, it could influence on rumen methanogenic population and hence, possibly mitigate methane production in swamp buffaloes fed on a rice straw based diet.