Objective was to evaluate the apparent digestibility of 2 commercially prepared pellets targeted for herbivores housed in zoological institutions (Mazuri Wild Herbivore Hi-Fiber Diet, Purina Mills International, Brentwood MO). The pellets, differing primarily in ether extract concentration, were designated low fat (LF; DM basis: 91% OM, 29% ADF, 46% NDF, and 5.9% EE) and high fat (HF; DM basis: 92% OM, 30% ADF, 48% NDF, and 10% EE). Dietary treatments consisted of 30% chopped Bermuda grass hay (Cynodon dactylon) and 70% commercial pellets. Using a crossover design, 13 male lambs (45.0 ± 4.8 kg BW) served as a model for ex situ ruminant herbivores. Lambs were offered diets at 90% of ad libitum intake for a 7-d adaptation and the subsequent 7-d fecal collection period. Ten percent of wet feces were retained, dried at 55 C, ground, and chemically analyzed. Daily intake of pelleted feed tended (P = 0.06) to be greater in sheep fed LF pellets (1040 vs. 1003 g DM/d); however, intake of total DM did not differ due to treatment (1434 ± 183 g DM/d). Apparent digestibility coefficients of DM (57 ± 1.8%) and OM (57 ± 1.8%) did not differ (P > 0.10) due to treatment. Apparent digestibility coefficients of NDF, ADF, and EE were greater (P < 0.01) for lambs fed HF pellets (42, 45, and 94%, respectively) compared with those fed LF pellets (36, 42, and 90%, respectively). Blood was collected via jugular vein approximately 4 h after feeding. Plasma concentrations of glucose (70 ± 2.0 mg/dL) and urea nitrogen (21.3 ± 1.1 mg/dL) were not affected (P > 0.10) by diet. To provide proper care and ensure optimal health of ex situ wildlife species, a clear understanding of the diet utilization by these species is necessary. Use of appropriate model species (i.e., closely related domestic counterparts) allows researchers to measure physiological data that might be otherwise unattainable due to research limitations when working with ex situ wildlife species (e.g., low numbers, control of variation, and sampling limitations). Herein, we utilized the sheep as a model for ruminants housed in zoological institutions.