High Se-containing forages grow on seleniferous soils in many parts of the United States and throughout the world. Selenium is an essential trace element that is required for many physiological processes but can also be either acutely or chronically toxic to livestock. Anecdotal reports of decreased reproductive rates in livestock grazing seleniferous forages have been reported and it has been speculated that reproductive failure is one of the initial changes of Se poisoning. The objective of this study was to determine the effect of high Se forages on reproductive rates in sheep. The study was conducted in 2 phases. Phase 1, the ewes (n = 3–5) were fed a Se-containing alfalfa pellet (made by adding western aster containing approximately 2000 ppm Se) that contained <0.3 (control),10, 20, 30, 45, or 60 ppm Se for 12 weeks. Feeding of the pellets began 6 weeks before exposing the ewes to rams. Each ewe was exposed to 2 rams twice each day for 2 complete reproductive cycles. At 35 to 45 d post-exposure the pregnancy status of the ewes was determined by ultrasound imaging. Each group fed Se-containing pellets had fewer pregnant ewes than the control group (pregnant ewes/ewes exposed): control (3/3), 10 ppm Se (3/5), 30 ppm Se (0/5), 45 ppm Se (1/5), 60 ppm Se (1/5). Throughout the study hair samples, blood samples, liver biopsies, and muscle biopsies were collected to monitor the Se status of the ewes. In phase 2, ewes were divided into 3 groups (n = 10) and were fed Se-containing pellets containing <0.3 (control), 10, and 30 ppm Se in the same manner and for the same period. However liver and muscle biopsies were not performed. After the first cycle, significantly (P < 0.05) more ewes were pregnant in the control group (10/10) than in the 10 ppm Se (6/10) and 30 ppm Se (6/10) groups. After a second cycle 9/10 and 6/10 were pregnant in the 10 and 30 ppm Se groups, respectively. None of the ewes in either phase of the study demonstrated any clinical signs of chronic Se poisoning during the study. In summary, high selenium forages containing 10 ppm Se or greater decreased reproduction rates in ewes when fed for 6 weeks before exposure to rams.