2006, Volume 12 No. 1

ARTICLE 10

Effect of Zinc Supplementation on Urea Hydrolysis in an In Vitro Fermentation Using Rumen Liquor

Kathirvelan C & Balakrishnan V
Department of Animal Nutrition, Madras Veterinary College, Chennai 600 007, India

ABSTRACT
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 ppm 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 (P<0.01) was observed in 10 ppm zinc supplementation over the rest of the treatments imposed across incubating hours. The residual urea (mg/dL) at the end of 1,2 and 3 hours of incubation were 28.99 ± 1.04, 18.33 ± 0.04 and 15.45 ± 0.18 respectively at 10 ppmn of zinc compared to 18.95 ± 0.38,10.00 ± 0.16 and 7.48 ± 0.12 in control (0 ppm). The result divulged that 10 ppm zinc was able to effectively retard the urea hydrolysis up to 3 hours, reflecting its effect on the extent of duration. Though the results demonstrated the superiority of 10 ppm zinc treatment over the rest of the treatments in retarding urea hydrolysis, yet another experiment was conducted to further improve the precision at a pH of 7.4 that is considered to be favorable environment for ammonia toxicity. The second trial was conducted following the same procedure except that of the level of zinc supplemented. In this experiment, zinc was supplemented at 0, 7.5, 10.0 and 12.5 ppm to 35 mg of urea with 40 ml of buffered rumen liquor incubated for 0,1,2 and 3 hours. The intial pH was brought to 7.4 by addition of a suitable quantity of soda bicarbonate to simulate a conducive environment for free ammonia production. The results of this experiment further strengthened the previous experiment's results with a significantly (P<0.01) higher residual urea in 10 ppm against the rest of the treatments. Thus it can be concluded that supplementation of 10 ppm zinc delayed the hydrolysis of urea.

Full Article >>