A review is given on the effects of the inclusion of Jack beans (Canavalia ensifomis L. DC) in poultry diets. Their use is restricted by the presence of a number of antinutritional factors which affect performance when consumed by poultry. The principals of these are identified as concanavalin-A (a lectin), canavanine and canaline (so-called non-protein amino acids), urease and saponins. The mechanisms of their toxicity and the rationale behind the methods that have been used to detoxify Jack beans are described. These mainly involve heat processing, but other approaches such as ensiling, fermentation and addition of chemicals have been applied. It is concluded that, although substantial improvements in nutritional value can result from a number of such treatments, processed Jack beans still contain a residual toxic component which results in depressions in growth rate, food intake and food conversion efficiency when they are included in poultry diets.
Three experiments were conducted in Merida, Mexico, between 1987 and1990 in which jack beans, treated in various ways, were included in chick diets at the rate of 300 g/kg diet. The diets were balanced by appropriate supplementation to provide the same concentrations of energy, minerals, vitamins and principal essential amino acids as control diets based on maize or sorghum and soyabean meal. Boiling jack beans or soaking and shaking them and the combination of boiling with soaking and shaking were studied with a view to removing or inactivating toxic factors and enhancing the utilization of the beans as a livestock feed. A fourth experiment was conducted to evaluate the contribution of canavanine to the deleterious effect observed when broiler chicks are fed diets containing treated jack beans and to examine the effect of canavanine on the efficiency of protein retention of broiler chicks.Boiling for 1 or 2 h reduced the toxicity of jack beans, but chick growth rate was only half that of controls. The combination of boiling, followed by soaking and shaking, removed most of the jack beans' anti-nutritional factors, but some toxic effects were left in the beans, causing a depression of c. 10% in feed intake and growth rate. Growth, feed intake and protein utilization of chicks were not affected when canavanine was added to a sorghum-soyabean diet at a level (3-5 g/kg diet) which matched the canavanine present in a diet containing 300 g/kg boiled jack beans.It was concluded that boiling was a satisfactory procedure for the inactivation of the heat-labile lectins in jack beans and that soaking and shaking was an effective method of reducing canavanine and the haemolytic activity of the saponins in jack beans. However, canavanine was found not to be the main toxic or anti-nutritional factor present in jack beans.
SUMMARYFour experiments were conducted in the Yucatán, Mexico, in 1991 and 1992 to study feed intake in 24 h trials with chicks and pigs fed diets containing either raw or treated jack beans or conventional diets with added canavanine.Feed intake of chicks in the first hour was markedly reduced and feed intake of pigs was severely reduced when raw jack beans (300 g/kg for chicks, 250 g/kg for pigs) were included in their diets. Feed intake of pigs diminished to a greater extent than that of chicks when treated beans (300 g/kg) were included in the diet. Short-term feed intake of chicks was not affected when canavanine (3·5 g/kg) was added to a sorghum-soyabean diet. However, pigs showed a large drop in feed intake when canavanine was added to a maize-soya diet at only 0·8 g/kg. It was concluded that in both species the anti-nutritional factors in jack beans cause a rapid reduction in feed intake which precedes a depression in growth rate. The initial feed intake depression in pigs could be partly attributed to canavanine remaining in the jack beans after treatment. In the chicks' case, however, rejection of a diet containing treated jack bean was due to anti-nutritional factor(s) other than residual canavanine.
Pennwalt Inc., a multinational chemical and pharmaceutical firm based in the United States, operates a chloralkali plant in Managua, Nicaragua. This plant utilizes elemental mercury in the production of chlorine and caustic soda for markets throughout Central America. The plant was recently found to be contaminating the waters of Lake Managua (on which the plant is located) with 2 to 4 tons of inorganic mercury effluent per year-over 40 tons in the 13-year history of the plant. Examination of the 152 workers employed in the plant showed that 56(37 percent) were suffering symptoms and signs of mercury poisoning, including tremors (in 45), memory and attention deficits (in 45) and paresthesias (in 52). Levels of airborne mercury vapor in the plant were found to range as high as 600 microgram/m3. (The airborne standard set by the U.S. Occupational Safety and Health Administration is 100 microgram/m3.) Workers in the plant had never been alerted to the hazards of mercury. The plant was found to be in deteriorated condition, with no recent investments in maintenance or modern safety equipment. It is reported that the parent corporation, Pennwalt, has been withdrawing capital from the operation (and from Nicaragua) since the fall of the Somoza regime.
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