Effect of Conservation Methods on Cyanic Acid Concentration and In Vitro Digestibility of Ceara Rubber (Manihot glaziovii) Leaves Ristianto Utomo, Subur Priyono Sasmito Budhi, Ali Agus, Cuk Tri Noviandi, Rico Fardhana and Maulana Osmar Sakti Faculty of Animal Science, Universitas Gadjah Mada, Yogyakarta, Indonesia Corresponding email: ristianto_utomo@ugm.ac.id ABSTRACT The objective of this experiment was to determine the effect of conservation methods on cyanic acid (hydrocyanic acid, HCN) concentration of ceara rubber (Manihot glaziovii) leaves. Two types of natural drying methods [dried indirectly (IS) or directly (DS) under sunlight] or 3 silage additives [without molasses (0M), with 4% molasses (4M), or with 6% molasses (6M); DM basis] were applied to chopped ceara rubber leaves; each treatment was replicated in 5 replications. Results showed that fresh ceara rubber leaves contain 18.59% crude protein, 20.04% crude fiber, 32.73% neutral detergent fiber, 9.45% ether extract, 45.91% nitrogen free extract, and 0.22% HCN (DM basis). Greater decrease of HCN were shown by ceara rubber leaves with DS treatment than those with IS treatment (89.89 vs. 84.40%, respectively; p<0.05). Both the 4M and 6M treatments decreased HCN concentration (32.8 and 32.9 vs. 28.2%, respectively; p<0.05) and decreased pH (4.26 and 4.20 vs. 4.41, respectively; p<0.05) compared with the 0M treatment. Drying methods and silage additives did not affect in vitro digestibility of ceara rubber leaves. Data from this experiment imply that lower HCN concentration in ceara rubber hay can be achieved by drying those directly under the sunlight; while in silage, the HCN concentration can be decreased by adding molasses during the ensilage process. Key Words: Ceara rubber, Hay, Silage, Cyanic acid, In vitro digestibility INTRODUCTION Cassava (Manihot esculenta) is classified as sweet or bitter. The bitter varieties contain greater cyanic acid (HCN) than the sweet ones (0.02 to 0.03 vs. ≤ 0.01%, respectively; Bo Gohl, 1981). It has been known that cassava leaves contain 18.5 to 26% dry matter (DM), 20 to 25.4% crude protein (CP), 18.4 to 21.20% crude fiber (CF), 71% total digestible nutrients (TDN), 7% ether extract (EE), and 40.6% non-nitrogen extract (NNE) (Bo Gohl, 1981; Utomo, 2012). However, the information of HCN content of cassava leaves is scarce. In addition to those type of cassava, there is another species of cassava which is leafy and having wide leaves named ceara rubber (Manihot glaziovii; Anonymous, -). This type of cassava is suspected having great HCN content. The objective of this study was to determine the effects of ensilage and hay-making process on the HCN concentration, chemical composition, and in vitro digestibility of ceara rubber leaves. MATERIALS AND METHODS Freshly harvested ceara rubber leaves were divided into 2 groups of treatment (hay-making and ensilage process). Leaves for hay-making were dried using natural drying methods [dried indirectly (IS) or directly (DS) under sunlight] with 5 replications for each treatment. The student test was used to compare the effects of treatments. Based on the one-way randomized complete design, fresh ceara rubber leaves were ensilage for 21 d with 3 different silage additives level [without molasses (0M), with 4% molasses (4M), or with 6% molasses (6M); DM basis]. Each treatment was replicated in 5 replications. Duncan multiple range test (Gomez and Gomez, 1984) were used to compare the effects of additive levels. Sustainable Livestock Production in the Perspective of Food Security, Policy, Genetic Resources and Climate Change 664