Transcriptome analysis of bovine granulosa cells of preovulatory follicles harvested 30, 60, 90, and 120 days postpartum.

The nutritional requirements of high-producing dairy cows increase rapidly in the weeks postpartum due to elevated milk production, and most cows enter a state of negative energy balance (NEB). Cows in this condition may preferentially divert nutrients away from reproduction, thereby experiencing a period of anovulatory anestrus, delayed ovulation of large follicles, and impaired fertility. To better understand the changes occurring in these large follicles as a function of time postpartum, granulosa cells from preovulatory follicles were collected at different times after calving: 30 days, 60 days, 90 days, and 120 days from a minimum of six animals at each time point. Three subjects for each period were selected for the analysis of the transcriptome, which was performed using a global bovine oligoarray microarray to identify differences in gene expression and cellular functions that occur in the follicular microenvironment during the progressive recovery from NEB in dairy cows. The time point 120 days was chosen as a reference period, as cows are then fully recovered from NEB. Data clustering indicated that the most different period from 120 days was 60 days with several 100 genes deregulated at that time. The principal cellular functions affected were cell proliferation, which was reduced, and deregulation of steroidogenesis, indicating immaturity of the follicles from the 60-day period relative to 120 days. One of the most interesting downregulated pathways was p38 mitogen-activated protein kinase, which is sensitive to the amount of retinoic acid or vitamin A, suggesting a possible treatment to improve postpartum fertility.