Effect of zinc supplementation on urea hydrolysis in an in vitro fermentation using rumen liquor

Rapid hydrolysis of urea in the rumen is the principle cause for urea (ammonia) toxicity. Efforts were directed to retard urea hydrolysis by supplementing zinc at gradual levels viz, 0, 5.0,10.0, 15.0 and 20.0 pprn in one ml solution to 35 mg of urea in one ml solution, and in one ml distilled water with 40 ml buffered rumen liquor in 100 ml syringe fitted with butyl rubber cap and incubated at 39OC. The 35 mg of urea per 43ml of liquor in the in vitro batch culture is equivalent to toxic dose of 100 mg per 100ml of rumen liquor in adult cattle. The incubation was carried out in an anaerobic environment at pH of 6.8. Five replications were conducted twice, resulting in ten replications in each treatment. The residual urea retained in each tube at 0, 1, 2 and 3 hour intervals from the respective aliquot (1 ml) was measured at wavelength of 520 nm. Highest residual urea (