The objective of this experiment was to determine the relationship between plasma AA concentrations and reproductive parameters of beef cows (n = 26). Two studies evaluating the effects of excess MP on reproductive function were compiled for this analysis. Non-pregnant, nonlactating mature beef cows consuming ad libitum corn stalks were offered a once-daily supplement designed to meet NRC NE_m and exceed MP requirements by 25–50%. After a 20 d adaptation period, cows were synchronized for ovulation using the 5-d CO-Synch + CIDR protocol. Ten days after synchronization, 100 µL of GnRH was administered to reset ovarian follicular growth. Daily transrectal ultrasonography was performed to diagram ovarian activity, and blood samples were taken for hormone and AA analyses. Corpus luteum (CL) volume was determined via ultrasound, and supplementation ended 7 d after estrus. Blood samples collected between d 47 and d 49 underwent AA analysis. Data were analyzed using the CORR procedure of SAS. No significant correlations were observed between AA profile and ovulatory follicle size or antral follicle count (P > 0.13). However, a positive relationship between length of proestrus and total AA (r = 0.49, P < 0.01) and total essential AA (r = 0.48, P < 0.01) was observed. In addition, a positive relationship between length of proestrus and total glycogenic AA, branched-chain AA, urea cycle AA, arginine, threonine, valine and isoleucine (r ≥0.44, P ≤ 0.04) were observed. As a percent of essential AA, leucine and phenylalanine were negatively correlated (r ≤ −0.39, P < 0.05) with length of proestrus. However, AA profile was not correlated with estradiol at estrus (P > 0.05). As a percent of total AA and essential AA, arginine was positively correlated with circulating progesterone 7 d post-estrus and ratio of progesterone to CL vol (r ≥0.41, P ≤ 0.04). Based on these data, total and essential AA concentrations may be related to several reproductive parameters around the time of ovulation; however, further research is needed to establish a causal relationship between individual AA and reproductive functions at ovulation.