*3.1. Nutrient Digestibility*

The apparent digestibility of crude protein was affected by dried grape pomace addition (Table 4). In the control group (C) a significantly lower digestibility coefficient of crude protein (*p* < 0.05), compared to the GP1 and GP2 was observed. This result corresponds with findings that were reported by some authors [18,19]. According to Guerra-Rivas et al. [11] the diet fed to the sheep (control vs. grape pomace) had minor effects on ruminal degradation parameters of crude protein. Ishida et al. [39] found lower digestibility of crude protein of grape pomace in comparison to the control diet (65.69 vs. 75.14%). It can be assumed that this was due to a higher proportion of grape pomace from dry matter intake (24% from dry matter intake of wethers). This trend was also confirmed by Abarghuei et al. [40] and Jayanegara et al. [41]. Differences in the digestibility of other nutrients between the control and experimental group GP1 were not significant. However, the apparent digestibility of nonfiber carbohydrates (NFC), organic matter (OM), and neutral detergent fiber (NDF) of the diets significantly (*p* < 0.05) increased by higher dose of dried grape pomace (C vs. GP2; NFC *p* = 0.018; OM *p* = 0.022; NDF *p* = 0.015). This trend of increasing the digestibility of organic matter and NDF, with an increase in their intake, was also confirmed by Bahrami et al. [42] and Foiklang et al. [16]. On the contrary, Baumgartel et al. [43] observed decreasing nutrient digestibility between basal and test diet including grape pomace. After the addition of GP to the ruminants' diets, higher OM digestibility was found [44].


**Table 4.** Digestibility coefficients (%) of the different feeding groups.

C: control, GP1: 1% addition of dried grape pomace from daily dry matter intake (DMI), GP2: 2% addition of dried grape pomace from daily DMI, CP: crude protein, EE: ether extract, CF: crude fiber, NFE: nitrogen free extract, NFC: nonfiber carbohydrates, OM: organic matter, ADF: acid detergent fiber, NDF: neutral detergent fiber.Different letters in row indicate statistical differences (Tukey test, *p* < 0.05); data are presented as mean ± SD.
