Laboratory, digestion, and growth studies evaluated urea as a source of ammoniation for quality improvement in guineagrass (Panicum maximum) hay. In a laboratory trial, 5.0-kg portions of hay were reconstituted with water to yield final forage moisture concentrations or 25 of 40% and treated with urea at 0, 4, 6, or 8% of the forage DM, with or without urease addition. Main effects of forage moisture or urease addition did not influence (P > .10) CP or NDF concentration or in vitro OM disappearance (IVOMD) of the guineagrass hay. Hay CP concentration and IVOMD increased linearly (P < .01), whereas concentrations of hemicellulose and ADL decreased linearly (P < .05) with increasing urea level. In other experiments, round bales of hay (320 kg) were reconstituted with water to yield final forage moisture concentrations of 25 or 40% and treated with urea at 0, 4, or 6% of the forage DM. The urea solution was applied as a spray onto the cut edges of the bales, or by low pressure (10 psi) injection. Two- and three-way interactions (P < .05) existed among forage moisture concentration, urea application method, and urea level for CP and NDF concentration and IVOMD of the guineagrass hay. Greatest enhancements in these forage quality characteristics were obtained when the urea solution was sprayed onto the hay at the 25% forage moisture concentration. In two digestion and two growth trials, round bales of hay were treated with 0, 4, and 6% urea sprayed onto the hay at the 25% forage moisture level. In each growth trial, 30 St. Croix white hair castrated male sheep (Trial 1:34 +/- 5.5 kg, Trial 2: 17 +/- 3.5 kg) were allotted to six pens of five head each, resulting in two pens per treatment. In the digestion trials, six similar sheep were used in a replicated 3 x 3 Latin square design. In the digestion and growth trials, hay intake increased in a quadratic (P < .05) manner with increasing urea level. Apparent NDF and ADF digestibilities increased linearly (P < .05) with increasing urea level. Linear improvements in ADG (P < .05) and gain/feed (P < .07) were observed with increasing urea level. Urea ammoniation offers potential for improving the feeding value of tropical forages and provides an option for quality forage during the dry season.