Effect of dietary energy restriction on follicular development and luteal function in nonlactating beef cows.

Twenty nonlactating beef cows were used to determine the effects of dietary energy restriction on ovarian follicular and corpus luteum (CL) development. Cows were fed to either gain (controls) or lose (restricted; RES) body weight. Observations continued until RES cows developed a subfunctional CL (progesterone [P4] < 1.5 ng/mL on d 10 of a cycle; n = 4) or had functional CL (P4 > or = 1.5 ng/mL on d 10 of a cycle; n = 6) followed by anestrus, at which time observations were discontinued on individual controls. Estrous cycles were then standardized for all cows. For RES cows developing subfunctional CL, cycle A was the cycle before development of the subfunctional CL, and cycle B was the 11-d period during development of a subfunctional CL. For RES cows with a functional CL, cycle A was the next to last cycle before anestrus, and cycle B was the 11-d period during formation of a functional CL. Daily P4 concentrations did not differ (P > .10) between controls or RES cows developing functional CL during cycle B but were lower (P < .05) in RES cows developing subfunctional CL. Ovulatory follicles and CL were smaller (P < .05) in RES cows during cycles A and B compared with controls. Daily IGF-l concentrations were higher on d 2 through 4 of both cycles in RES cows developing functional CL compared with RES cows developing subfunctional CL (P < .05). Feeding diets limited in energy resulted in two types of CL. These differences may have been due to IGF-I concentrations.