115 Microbial Protein Synthesis in Ongole Crossbred Cattle Fed on Fibrous Feeds (Suprayogi) SINTESIS PROTEIN MIKROBA SAPI PERANAKAN ONGOLE YANG DIBERI PAKAN BERSERAT (Microbial Protein Synthesis in Ongole Crossbred Cattle Fed on Fibrous Feeds) W.P.S. Suprayogi Fakultas Pertanian Universitas Negeri Sebelas Maret, Surakarta ABSTRAK Penelitian ini bertujuan untuk mengetahui sitesis protein mikroba sapi peranakan Ongole (PO). Penelitian menggunakan enam ekor sapi PO betina guna pengukuran sintesis protein mikroba. Setiap pakan yang diteliti diberikan secara tunggal, yang terdiri atas jerami kacang tanah (JKT), rumput raja (RR) dan hijauan jagung (HJ), secara ad libitum. Data sintesis protein mikroba dianalisis dengan metode rancangan acak kelompok cross over (‘complete block cross over design’). Hasil penelitian menunjukkan bahwa konsentrasi derivat purin dan sintesis protein mikroba dari ketiga jenis pakan berbeda nyata (p < 0,05). Konsentrasi derivat purin untuk JKT, RR, dan HJ masing-masing adalah 52, 42 ; 44, 42 dan 41, 89 mmol/ekor/hari. Sintesis protein mikroba adalah 25,66 ; 18,25 ; dan 15,62 g N/ekor/hari masing-masing untuk JKT, RR, dan HJ. Berdasarkan hasil penelitian dapat disimpulkan bahwa jerami kacang tanah memberikan kontribusi protein mikroba pada sapi PO yang lebih tinggi dibanding rumput raja dan hijauan jagung. Kata kunci : pakan tunggal, sapi PO, sintesis protein mikroba ABSTRACT Six Ongole cross bred cattle were used to determine microbial protein synthesis. The cattle were fed on ground peanut straw (PS), king grass (KG) and corn forage (CF) ad libitum as single feed. The values of microbial protein synthesis was analysed using complete block cros over design. The results showed that purin derivative concentration and microbial protein synthesis were significantly different (p < .05) among feeds. The purin derivative concentration of cattle fed on PS, KG and CF were 52,42 ; 44,42 and 41,89 mmol/day, respectively. The production of microbial protein synthesis respectively for PS, KG, and CF were 25,66 ; 18,55 ; 15,62 g N/day. It could be concluded that ground peanut straw gave higher microbial protein synthesis than king gras and corn forage. Keywords : single feed, ongole cross bred cattle, microbial protein synthesis