**6. Some effects of legumes containing urease used as animal feed**

It has been estimated that *G. max* meal accounts for about 67% of the total sources of protein utilized in feeds of animal around the globe [104], because of majorly its high concentration of protein which is around 44–48% [105]. Nonetheless, *G. max* possesses an unusual high amounts of bioactive compounds having antinutritional or/and properties that are toxic, that possesses on the body of animals' metabolism a negative effect [106]. The content of urease was not different evidently among 11 tested soybean cultivars [107]. Contrarily, the content of urease was found to vary among several other soybean cultivars [108–110], and the urease levels positively correlated with antinutritional effects in rats [109]. The negative effects of utilizing meals containing urease as feed for animals are reported. Urea is regularly mixed with the feed of animals and, when *G. max* that are not processed are mixed with urea, the activity of urease will enabled the release of ammonia, which is an effect that is not desired in a feed that are mixed [111]. In ruminant animals, ammonia quickly enters the blood which can cause affects that is adverse ranging from depressed feed intake and performance of the animal, to Mortality due to toxicity of ammonia [112]. In dairy cows, the liver whose responsibility is remove potentially toxic ammonia from circulation, was able to remove ammonia added to portal blood until the supply was up to 182 mg/min but, at infusion rates that is high, peripheral blood

#### *Function of Urease in Plants with Reference to Legumes: A Review DOI: http://dx.doi.org/10.5772/intechopen.102646*

concentrations of ammonia increased, supporting the assessment that a rapid hydrolysis of dietary urea can rise above the capacity of the liver to remove it [113]. In chickens, it was shown that meals of *G. max* from a particular source regularly produced a high incidence of tibialdyschondroplasia (TD) and the major striking difference between the meals was the high antitrypsin and values of urease in those that induced the disease [114]. TD incidence was previously shown in broilers to increase when 1.5 or 30% ammonium chloride was added to the feed [115], meanwhile it was not shown when calcium chloride was added [116]. These could indicate that the ammonia released by urease may a function in TD incidence on meals of *G. max* fed on chickens. For addition of nitrogen supplement to be allowed in the feed of animals, so as to protect the animals from the production of high ammonia level which is toxic, there is need for pretreatment of the *G. max* meal. The major method used is the treatment by heat to do away or reduce the anti-nutritional effects and/or factors that are toxic in *G. max*, which include urease [103, 117], meanwhile these treatments should be kept at a low level, because it may be possible to destroy some important constituents of the seed [106]. To do away with the activity of urease, many effective treatments are required, which includes steam-heating at 120°C for 7.5 min or at102°C for 40 min [103], boiling for 60 min. at 92°C [109], and dry-heating at 100°C and 2 kgf/cm<sup>2</sup> for 60 min [117]. All these treatments do away with the activity of urease, coupled with a reduction of many anti-nutritional factors. The best method to evaluate the processing adequacy and final quality of the *G. max* meals is by conducting biological tests. Nevertheless, the required time, complexity and cost of these tests have negative effect their use. From 1940s, the use of urease test has been in existence as an indirect method of evaluating the adequacy processing *G. max* using heat because it is fast, require minimum skill and minimum amount of laboratory equipment. A discovery revealed a correlation that is high among trypsin inhibitors activities, lectins and urease, which indicate that the *G. max* processing can be estimated adequately by these analytical criteria to a considerable extent. In the past years, several guidelines were developed to facilitate the measurement of urease activity [103]. These guidelines are used to quantify directly or indirectly the amount of ammonia released. The one that was first developed is the method by Caskey-Knapp [118] in a buffer solution the meal is incubated with urea and then the addition of phenol red. Meals that are not properly processed will lead to an increase in the pH of the solution after incubation, which will be observed by a change in color of the solution from red-orange to pink, but meals that are well processed will show a little or no color change. A study suggested another alternative method, having the potential to distinguish meals with low levels of the activity urease, based on the meal incubation with urea in a buffered solution and using colorimeter to determine the urea residual with *p*dimethylaminobenzaldehyde [119]. Also, a method was propose d for direct titration of ammonia as a measure of urease activity [120] and adapted [121], whereby urea incubation with the meal is carried out, maintaining the pH of the solution by adding HCl slowly. The system is therefore titrated with NaOH. The difference in titration between a urease inactivated (control) and the sample is considered as the urease activity of the meal. Other two methods were developed for determination of ammonia directly, which is based on phenolhypochlorite reaction [122, 123]. So many adaptations and modifications of these methods were developed as time passes by. Meanwhile, regardless of the method used, the activity of urease is a very good indicator of *G. max* meals that are not properly processed. This method could also be applied to other meals suspected to contain urease. However, this activity is not a good indicator *G. max* meals that are over processed.
