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Effect of Rhodanese Enzyme Addition on Rumen Fermentation, Cyanide Concentration, and Feed Utilization in Beef Cattle Receiving Various Levels of Fresh Cassava Root

Fresh cassava root is not recommended for animal feeding due to high quantities of hydrocyanic acid (HCN), which produces symptoms of poisoning. The purpose of this study was to find out how a rhodanese enzyme addition affects rumen fermentation, HCN content, feed utilization, and blood metabolites in beef calves fed fresh cassava root. Four Thai native beef cattle with an initial body weight (BW) of 95 ± 10.0 kg (1–1.5 years old) were randomly allocated to receive fresh cassava root containing HCN at 0, 300, 450, and 600 ppm according to a 4 × 4 Latin square design. Rice straw was the basal diet. The rhodanese enzyme was combined with concentrated feeds at a concentration of 1 mg/104 ppm HCN. The fresh cassava root was cleaned to remove dirt and chopped into 3 to 5 mm sized pieces before being fed to the animals at their various levels. The total feed intake of beef cattle increased when fed with fresh cassava root (p < 0.05). The digestibility of crude protein (CP) was different among various fresh cassava root levels (p < 0.05). Ruminal ammonia-N levels were measured 4 hours after feeding, and the average concentration declined considerably in animals fed fresh cassava root at 300–600 ppm HCN (p < 0.05). Cyanide concentration in the rumen was linearly increased by 270.6% (p < 0.05) when it was supplemented with a high level of fresh cassava root. Blood urea-N concentration was altered and decreased when supplemented with fresh cassava root (p < 0.01). The blood thiocyanate concentration was altered by the levels of fresh cassava root and rhodanese enzyme, which ranged from 4.1 to 27.9 mg/dL (p < 0.01). Cattle given fresh cassava root showed no influence on total volatile fatty acid, acetic acid, or butyric acid concentrations in the rumen (p > 0.05). However, the concentration of propionic acid increased slightly (p < 0.05) 4 hours after feeding. Supplementing fresh cassava root up to 600 ppm HCN/day improved N absorption, retention, and the proportion of N retention to N intake (p < 0.05). Therefore, increasing the inclusion of fresh cassava root with a rhodanese enzyme addition improves total feed intake, CP digestibility, nitrogen utilization, blood thiocyanate, and propionate concentrations, which may remove HCN without harming animal health.