123 Caraka Tani: Journal of Sustainable Agriculture, 37(1), 123-131, 2022 URL: https://jurnal.uns.ac.id/carakatani/article/view/55136 DOI: http://dx.doi.org/10.20961/carakatani.v37i1.55136 ISSN 2613-9456 (Print) 2599-2570 (Online) Copyright © 2022 Universitas Sebelas Maret The Utilization of Coconut Coir as Supplementary Feed for Beef Cattle Production Limbang Kustiawan Nuswantara 1 , Sunarso 1 , Mukh. Arifin 1 and Agus Setiadi 2 1 Department of Animal Husbandry, Faculty of Animal and Agriculture Science, Universitas Diponegoro, Semarang, Indonesia; 2 Department of Agriculture, Faculty of Animal and Agriculture Science, Universitas Diponegoro, Semarang, Indonesia * Corresponding author: limbangkustiawannusw@lecturer.undip.ac.id Abstract High feed price is a major problem in the production of beef cattle. Therefore, this study aims to determine coconut coir's technical and economic potential for beef cattle feed. This is an in vivo and in vitro study that involved 95 days trial period and 16 male Brahman crossbreed cattle weighing 134±12.1 kg. The coconut coir was fermented using buffalo rumen liquid and was termed fermented coconut coir (FCC). A randomized block design was used in this research, including four feed treatments, namely complete feed D1 using 15% FCC, D2 using 20% FCC, D3 using 25% FCC and D4 using 30% FCC. The parameters observed were technical performance (protein, dry and organic matter intake), ruminal fermentability, purine derivatives and economic performance. The data were analyzed using analysis of variance and Duncan's multiple range test for posthoc multiple comparisons. The results showed that the intake of beef cattle feed D1, D2 and D3 was higher than D4. Furthermore, the digestibility of D1, D2 and D4 was higher than D3. The purine derivatives of D2 were the highest but not significantly different (P > 0.05) from D1 and D4. In addition, the ruminal fermentability was not significantly different (P > 0.05) among treatments. Moreover, the beef cattle feed on D2 had the best economic performance. The performance results showed that ruminal fermentability, purine derivatives and economic performance of D2 (20% FCC) gave the best results but were not statistically different (P > 0.05) from other variables. Conclusively, coconut coir can be used as beef cattle feed without causing health problems. Keywords: coconut coir; economic performance; purine derivatives; ruminal fermentability; technical nperformance Cite this as: Nuswantara, L. K., Sunarso, Arifin, M., & Setiadi, A. (2022). The Utilization of Coconut Coir as Supplementary Feed for Beef Cattle Production. Caraka Tani: Journal of Sustainable Agriculture, 37(1), 123-131. doi: http://dx.doi.org/10.20961/carakatani.v37i1.55136 INTRODUCTION Coconut is a common multifunctional found in Indonesia found on the North Coast of Java, growing from Banten Province to Banyuwangi Regency. Furthermore, it is spread across many Asian countries and is widely used as food, drinks, biodiesel and even cosmetics (Ramesh et al., 2021). Coconuts' production worldwide covers more than 10 million hectares, distributed in 92 countries. Indonesia, India and the Philippines  Received for publication September 16, 2021 Accepted after corrections January 22, 2022 account for nearly 75% of its production worldwide. Indonesia has become the largest coconut producer in the globe. One of its available biomasses is coconut coir, which has a high calorific value in the form of lignin and cellulose and consists of charcoal, pyroligneous acid, tar, gas, potassium and tannin (Zafar, 2021). Generally, coconut coir has a great potential to be used as ruminant feed. Coconut coir is primarily used for direct combustion to generate heat; otherwise, it is just