Dietary Supplementation with Mitragyna speciosa Leaf Powder and Saccharomyces cerevisiae Improves Nutrient Digestibility, Rumen Fermentation Efficiency, and Microbial Nitrogen Supply in Thai Native Beef Cattle

This study evaluated the effects of Mitragyna speciosa leaf powder (MSP) and Saccharomyces cerevisiae (SC) supplementation on nutrient intake and digestibility, rumen fermentation, microbial populations, and microbial protein synthesis in Thai native beef cattle. Four female Thai native cattle (130.0 ± 7.4 kg body weight at the start of the experiment) were randomly assigned in a 4 × 4 Latin square design to four dietary treatments: (T1) total mixed ration (TMR) alone (control); (T2) TMR + MSP at 10 g/head/day; (T3) TMR + SC at 10 g/head/day; and (T4) TMR + MSP at 5 g/head/day + SC at 5 g/head/day. A TMR containing 14% crude protein was offered ad libitum throughout four 21-day periods. Total dry matter intake and nutrient intakes did not differ among treatments (p > 0.05), although the planned contrast between the control and the supplemented treatments indicated a small shortfall in the control for dry matter intake (p = 0.041). Apparent total-tract digestibility of dry matter, organic matter, crude protein, and acid detergent fiber was higher in supplemented animals than in the control (p < 0.05), and neutral detergent fiber digestibility tended to increase (p = 0.052). Ruminal pH increased, significantly so in the two treatments containing SC (p = 0.001), whereas ruminal ammonia nitrogen and blood urea nitrogen decreased with supplementation (p < 0.05). Total volatile fatty acid concentration was unchanged, but the propionate proportion increased and estimated methane production decreased (p < 0.05). Total bacterial counts increased and protozoal counts decreased with supplementation (p < 0.05), while fungal counts were unaffected. Urinary purine derivative excretion and absorption increased with supplementation, and microbial nitrogen supply rose from 24.66 to 34.21–35.93 g N/d (p = 0.002). The efficiency of microbial nitrogen supply rose from 15.44 to 19.30–20.07 g N/kg of organic matter digested in the rumen (p = 0.007). Supplementation with MSP and SC, alone or in combination at 5 g of each, therefore enhances nutrient digestibility and rumen fermentation efficiency in Thai native beef cattle without depressing intake.