In a completely randomized design with a factorial arrangement, three energy supplements and two species (cows and ewes) were evaluated in two identical experimental periods: gestation and lactation. The three supplement treatments were a control, barley, and sugar beet pulp (SBP). The basal diet was tall wheatgrass straw (5.52% CP). Forage and total dry matter intake (FDMI and TDMI, respectively) interacted (P=.04) with species, supplements, and physiological stages. An interaction of physiological stage and sampling time occurred for pH. Supplement and sampling time interacted for butyric acid proportion and total VFA concentration. Diet digestibility displayed an interaction between species and physiological stage. Digestibility was lower during lactation than gestation for cows, but similar for ewes. Retention time interacted for species, supplement, and physiological stage. Fill of the gastrointestinal tract responded to physiological stage. Fill of the gastrointestinal tract responded to physiological stage, with values of .80 and 1.36% BW for gestation and lactation, respectively. Methane output displayed an interaction between species and physiological stage when data where analyzed as g CH4 d-1kg-1 BW. The highest and more variable values in CH4 losses were from ewes. From gestation to lactation, both species increased CH4 production. Energy lost in feces responded to physiological stage (P=.0008). Across species and supplements, 48 and 60% of the GEI were lost as feces during gestation and lactation, respectively. The use of energetic supplements in ewes depresses FDMI in late gestation, but stimulates it during lactation when a diet based on low-quality forage is fed. For cows, the use of energetic supplements does not affect FDMI during late gestation or lactation. The source of energy does not have an effect, and thus the decision will depend on the cost of supplements. Intake is more strongly affected in ewes than cows when low-quality forage is used. However, for both species, dry matter intake (DMI) is strongly depressed in late gestation.