The issue of ruminant livestock feed shortages can be addressed by utilizing innovative feed that is both nutritionally rich and available year-round. The study aimed to examine how silage influences the growth performance of thin-tailed sheep. The study was conducted in Sleman, Yogyakarta. The study involved thirty thin-tailed ewes, aged 10 to 12 months and weighing 15.03±1.09 kg. A completely randomized design (CRD) with a unidirectional arrangement was applied, involving three diet treatments and ten replications. In this study, the silage consisted of Pennisetum purpureum cv. Gama Umami and Calliandra calothyrsus in a 70:30 ratio, respectively. The diets were as follows: T0 = 60% concentrate and 40% water spinach straw, T1 = 40% concentrate and 60% silage, and T2 = 60% concentrate and 40% silage. The study focused on variables such as growth performance, apparent nutrient digestibility, and nitrogen (N) utilization. The data were examined through analysis of variance (ANOVA), followed by Duncan’s new multiple range test (DMRT) for comparisons of significant differences. The performance indicators for treatments T0, T1, and T2 were as follows: dry matter intake (DMI) of 57.99, 60.12, and 65.57 g/kg LW0.75/day, respectively; crude protein intake (CPI) of 5.98, 8.36, and 6.78 g/kg LW0.75/day; average daily gain (ADG) of 38.96, 43.94, and 49.10 g/sheep/day; N intake of 0.90, 1.34, and 1.09 g/kg LW0.75/day; N digestible of 0.70, 0.95, and 0.80 g/kg LW0.75/day; and N retention of 0.56, 0.85, and 0.70 g/kg LW0.75/day. Therefore, no single dietary treatment was universally superior, but each offered unique advantages.