The study aimed to see if adding fermented palm press fiber to rice straw could improve how well cows can digest it. They tested different amounts of the fiber and looked at how it affected the digestibility of dry matter, organic matter, crude protein, and crude fiber in the rice straw. They also checked the levels of ammonia and VFA in the cows' stomachs after eating the treated straw. The results showed that while dry matter and crude protein digestibility stayed the same, organic matter and crude fiber digestibility improved with the fiber supplement. The number of bacteria in the cows' stomachs also tended to increase with the fiber supplement.