عنوان مقاله [English]
Introduction Urea is a small organic compound that is very rich in N (44.96% N) and is used to supply degradable intake protein (DIP) for ruminants. Urea is broken down to ammonia in the rumen under the action of urease bacteria. Using urea over other sources of DIP is cheaper according to per N basis than any other feedstuffs. However, urea is used rather inefficiently by ruminants compared with other sources that contain true protein, and this is due to the fact that the rate of urea degradation in the rumen is more rapid than the rate of utilization of the resulting ammonia by rumen bacteria. One strategy for improving the utilization of urea by ruminants is reducing the degradation rate of urea. A number of slow release urea products were developed for this purpose. Coated urea is a urea product design to reduce the rate of ruminal degradation of urea. The objective of this research was to investigate the effects of coated urea on N metabolism and determine this Effect in ruminant feed.
Materials and Methods to characterize the ruminal behavior of coated urea three experimental studies were designed. Two in vitro studies were designed to determine NH3-N release and gas production difference in treatments. NH3-N release of each Optigen and coated urea was tested in sex liquid phase included: distilled water, TCA (Ph = 6.2), buffer solution, buffered rumen fluid, Free cell rumen fluid (centrifugation at 7000 rpm), Free cell buffered rumen fluid. Each of the two N-sources was isonitrogenous (equivalent 20mg urea) and added to a 100-ml glass syringe. Then 30 ml of solution (consisting distilled water, TCA, buffer solution, buffered rumen fluid, free cell rumen fluid or free cell buffered rumen fluid) was pipetted into each syringe followed by incubated in a water bath at 39°C. Three syringes for each treatment diet were incubated for 0, 30 min and 2, 4 and 6 h time points. The syringes were taken out and Residual solid parts were taken for determination of NH3-N release using the Kjeldahl N methods (AOAC, 2005). The gas production of each N-Sources (four N-Sources in triplicate) was tested in 4 different feed mixtures (straw + 3% N-Sources, barley flour + 3% N-Sources, barley flour + molasses as additives + 3% N-Sources, a dairy ration formulated to + 3% N-Sources). The in vivo experiment was conducted using sixteen dairy Sannen goats with an average body weight of 38.85 kg, 73 days of lactation and 1979g milk production. The experimental design was a completely randomized design. The experiment consisted of 21-day periods each consisting of 14 days adaptation and 7 days of sampling. The experimental rations were: 1) control (canola), 2) urea (urea % 0.5), 3) Optigen (Optigen %0.55), 4) coated urea (% 0.7 coated urea).
Results and Discussion Based on these results, urea is often degraded rapidly in the rumen by the action of urease and the resulting ammonia supply may exceed the capacity of rumen bacteria to assimilate it into amino acids. This rapid release of ammonia may result in inefficient N utilization in the rumen. Therefore coated urea improves ammonia assimilation in the rumen. The cumulative gas production (96 hours) influenced by diet and N-source treatments, which was higher in formulated TMR diets for the dairy cow and least gas production in wheat straw. The result indicated that Optigen (90.82) and then coated urea (90.81) were the highest gas producer in the formulated TMR diets for the dairy cow and the canola meal (69.04) and urea (69.43) had the least gas production in wheat straw (P<0.05). The results showed that treatments had no significant effect on milk compositions, rumen fermentation and synthesis of microbial protein (p> 0.05). The impact on the most blood metabolites except BUN, Cholesterol and ALT were also no significant (p> 0.05). As a result, no significant differences observed between coated urea with control (canola) treatments.
Conclusion it was concluded that little difference was observed in gas production results between coated urea and Optigen treatments with control (canola). And therefore to reducing feed costs and increasing the efficiency of the rumen microorganism, we can use NPN sources as a replacement for part of dietary protein.