The aim of this study was to evaluate the effects of pegbovigrastim injection (Imrestor, Elanco Animal Health, Greenfield, IN) on behavior and time to first detected heat. The study was conducted on a commercial Mississippi dairy from August 21, 2017, to March 31, 2018. Initially, a total of 270 cows were blocked by parity group (multiparous or primiparous) and randomly assigned to control (CON, n = 144) or treatment (IMR, n = 126). Study animals were equipped with smart leg and smart neck tags (Nedap, the Netherlands). The leg tag measured lying time, walking time, and leg activity with a 3-axis accelerometer, and the neck tag measured heat activity. At 10 ± 2 d before expected calving and again at calving, treated cows received 2.7 mL of Imrestor and CON cows received 2.7 mL of 0.9% saline. Cows were body condition (BCS), hygiene (HYG), and lameness (LAM) scored weekly. The Nedap system created heat alerts based on individual behavior changes. Weekly summations of the number of steps, time spent lying down and walking (min) was then utilized to determine weekly means of these variables since calving until 60 DIM. Unfortunately, because of malfunction in the data synch between tags and the farm software, data from only 61 cows were utilized in the analysis (CON = 43 and IMR = 18). The MIXED procedure of SAS was utilized to compare the leg activity, walking time, and lying time between the 2 treatment groups. The mixed models included fixed effects of treatments and block, and random effect of cow within block. A Cox proportional hazards regression was used to determine the relative likelihood of cows displaying estrus within their first 60 DIM. Imrestor treatment did not alter the hazard ratio of estrus occurrence during the first 60 DIM (hazard ratio = 0.99, 95% CI = 0.84 to 1.7, P = 0.88). The median calving-to-first detected heat interval for IMR and CTR cows was 47 and 46 d, respectively (P = 0.45). Imrestor treatment did not affect time spent lying, walking, or amount of steps given (P = 0.54, 0.59, and 0.48, respectively). In conclusion, IMR treatment did not affect the behavior or time to first detected heat in study cows.