Evolution of the ethanol industry will likely result in future distiller’s grains feedstuffs that are more concentrated in crude protein (CP) and less concentrated in fat. However, the direct effects of excess dietary CP on reproductive function in beef cows have not been adequately addressed. In the present study, we observed that excess dietary CP derived from a rumen undegradable protein (RUP) abundant feedstuff impacted ovarian follicular growth patterns and affected follicular estradiol production and circulating concentrations of progesterone in the subsequent estrous cycle. The mechanisms by which these physiological and endocrine changes occur as a result of excessive RUP supplementation have not been fully elucidated. However, the need exists to continue research to determine how CP from these feedstuffs, when fed as a supplemental energy source in low quality forage-based diets, may impact reproductive efficiency in the beef herd.