The aim of this study was to assess the effects of different inclusion levels of raisin waste (RW) in the diet on the animal performance and ruminal fermentation parameters of growing lambs. Four levels of RW inclusion (i.e., R0, R1, R2 and R3 for 0, 100, 200 and 300 g RW kg–1 dry matter of diet, respectively) were tested. The experimental diets were fed to 24 male lambs (six months old) and six animals were allocated to each treatment. In the first experiment, effects of different levels of RW on the animals’ performance, some rumen parameters and protozoa populations were studied. In the second experiment, the apparent total tract digestibility of diets and nitrogen balance were measured. The highest final body weights were observed for the R2 and R3 diets. The R3 diet had the lowest dry matter intake (1156 vs. 1303 g day–1 for R3 and R0, respectively) and feed conversion rate (6.4 vs. 8.7 for R3 and R0, respectively). Total number of protozoa increased with the addition of RW, but Epidinium spp. completely disappeared with the R3 diet. Inclusion of RW at levels higher than 200 g RW kg–1 DM of diet significantly reduced crude protein (p = 0.042) and neutral detergent fiber digestibility (p = 0.049). Our findings showed that RW could be included in the diets of growing lambs up to 200 g kg–1 DM without compromising their production performance.
