This study aimed to evaluate the effects of adding dried distillers' grains with solubles (DDGS) to the nutritional regimens of ewes at different time periods on reproductive traits, serum hormones and serum metabolites. In Experiment 1, 100 ewes were divided into 4 groups (n=25) according to diet. The four diets were grass hay (H) alone (group H), H with barley (group H+B), H with DDGS for the whole feeding period (27d) (group H+DDGS) or H and DDGS for 5d (d 8-12 of oestrus cycle) (group H+DDGS5). Serum progesterone concentrations were affected by oestrus cycle (p<0.001), but not by dietary treatments. However, feeding H+DDGS caused significant increases in serum insulin, leptin and growth hormone concentrations (p<0.05). In Experiment 2, 30 ewes were divided into 2 groups (n=15), receiving DDGS or soybean meal (SBM) during the prepartum period. Diets had no significant effect on weights of dams or lambs at birth; however, the weaning weights of lambs born from ewes of group DDGS were significantly higher (p<0.05). Moreover, serum glucose, blood urea nitrogen, triglyceride and beta hydroxybutyric acid (BHBA) concentrations during the prepartum period were affected by dietary treatments and by time (p<0.001). During the prepartum period, BHBA concentrations of ewes fed SBM were higher, while BHBA levels decreased during the last weeks of pregnancy regardless of diet. Lamb serum immunoglobulin G concentrations increased from 1h to 24h after birth (p<0.001). Colostrum of ewes fed SBM had higher fat-free dry matter (DM) and protein contents in comparison to colostrum of ewes fed DDGS (p<0.05). In conclusion, DDGS can be included as protein source in pregnancy rations up to 15% of DM to obtain reproductive performance outcomes equal to or exceeding those obtained with SBM.