The effect of urea on the preservation and digestibility in vitro of perennial ryegrass

Mature perennial ryegrass with a digestible organic matter in vitro (DOM) content of 544 kg^?1 dry matter (DM) and a DM content of 568 g kg^?1 was treated with urea prills at 0, 30 and 60 kg^?1 DM. Packages, each containing about 4 kg DM, were stored either aerobically for 120 days or anaerobically for 60 days followed by 60 days of exposure to air. Temperature, DM losses and changes in chemical composition were measured.Urea hydrolysed rapidly to ammonia and there was no benefit from an additional supply of urease enzyme. When no urea was added, aerobic storage resulted in heating and the loss of up to 25% of the initial weight of DOM. Treatment with urea reduced these effects, the DOM loss declining to approximately 10 and 3% for the low and high levels of urea, respectively. During the anaerobic period these treatments produced a gain in DOM of, respectively, 3.4 and 8.9%. It is concluded that urea can be a useful preservative for moist materials which may also improve the feeding value of mature crops.