Abstract
Two experiments were undertaken to screen for ruminal cyanide-utilizing bacteria (Experiment 1), and to evaluate the influence of fresh cassava root (FCR) and pellets containing high sulfur (PELFUR) on cyanide content, gas production parameters, in vitro degradability, and ruminal fermentation (Experiment 2). Experiment 1 was conducted in a completely randomized design (CRD) for the screening of cyanide-utilizing bacteria and the dietary treatments consisted of cyanide at 0, 150, 300, and 450 ppm. In Experiment 2, a 5 × 3 factorial arrangement in a completely randomized design was used for the in vitro study. Factor A was the level of FCR at 0, 260, 350, 440, and 530 g/kg of dry matter (DM) substrate, and factor B was the level of PELFUR at 0, 15, and 30 g/kg DM substrate. In Experiment 1, adding different doses of cyanide significantly affected cyanide-utilizing rumen bacterial growth (p < 0.05). Increasing the concentration of cyanide from 0 to 150 and 150 to 300 ppm resulted in increases in cyanide-utilizing rumen bacteria of 38.2% and 15.0%, respectively. In Experiment 2, no interaction effects were found between FCR and PELFUR doses on gas production parameters (p > 0.05). Increasing the FCR level to more than 260 g/kg of DM substrate could increase cumulative gas production (p < 0.05). Increasing doses of PELFUR from 15 to 30 g/kg increased the cumulative gas production when compared with that of 0 g PELFUR/kg of DM substrate (p < 0.05). The cyanide concentration in rumen fluid decreased with PELFUR (p < 0.05) supplementation. Degradability of in vitro DM and organic matter following incubation increased at 12 and 24 h due to PELFUR supplementation with FCR and increased additionally with 15 g PELFUR/kg of DM substrate (p < 0.05) in 440 g FCR/kg of DM substrate. Proportions of the total volatile fatty acids, acetic acid (C2), propionic acid (C3), and butyric acid among supplementations with FCR (p < 0.05) were significantly different. In conclusion, the present results represent the first finding of bacteria in the rumen that are capable of utilizing cyanide, and suggests that cyanide might function as a nitrogen source for bacterial cell synthesis. The inclusion of FCR of 530 g/kg with 30 g PELFUR/kg of DM substrate could increase the cumulative gas production, the bacterial population, the in vitro degradability, the proportion of C3, and the rate of the disappearance of cyanide.
Highlights
It could be assumed that cyanide is used by the bacteria as a nutrient for their growth, with cyanide acting as a nitrogen source
This finding is consistent with a study by Razanamahandry et al [27] which showed that certain bacteria are capable of using cyanide as a nitrogen source through enzymes which catalyzed the conversion of the sulfur species to rhodanese and mercaptopyruvate sulfurtransferase
This could be due to the addition of cyanide up to 450 ppm resulting in high bacterial toxicity and inhibiting cytochrome oxidase and interfering with some of the key biochemical reactions and activities [28]
Summary
Cassava root, is used for animal diets, especially in the tropical region [1]. It can be used for human food and as an energy ingredient in animal diets. Cassava root is sliced and sun-dried, called cassava chip, prior to its use as an ingredient in animal diets. Cyanogenic compounds contained in cassava roots, including linamarin and lotaustralin, are constraints for FCR usage. These compounds, cyanohydrins, are produced via a hydrolysis process, starting with linamarin as a precursor to linamarase
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