During the transition period, dairy cattle go through intense physical and metabolic changes. The circadian timing system (CTS), functions to coordinate internal physiology including metabolic processes, therefore, disruption of the CTS, is associated with changes in metabolism. Our objective was to determine if disrupting the CTS from 35 d before expected calving (BEC) until calving affected muscle and adipose tissue mobilization in dairy cattle. In a completely randomized design, 32 multiparous cows were blocked by lactation number, disease incidence from previous lactation and assigned to 1 of 2 treatments, control (C) or phase-shift (PS). C were exposed to 16 h light:8 h dark. PS were exposed to the same amount of light and dark however, every 3 d there was a 6-h shift in the light-dark cycle. BW, BCS, back fat thickness, and muscle depth were measured on 35, 21, and 7 d BEC and 0, 10, 30 and 60 d postpartum (PP). Blood samples were collected on 35, 21, and 7 d BEC and 0, 2, 5, 9, 15, and 22 d PP and analyzed for NEFA, 3-methyl-histidine (3MH), and creatinine. Data were analyzed using the Mixed Procedure of SAS v.9.4 with the fixed effects of treatment, time point, and their interaction and the random effect of cow nested within treatment. There were no treatment differences for BW, BCS, or NEFA (all P > 0.25). There was a significant effect of time point on BCS, BW, and NEFA (P < 0.0001), with a mean loss of 97.6 kg of BW and 0.69 points of BCS from calving to 60 DIM. Cows mobilized 19.1% of their muscle depth and 50% of their subcutaneous body fat from 7 d BEC to 60 DIM. C cows had greater muscle depth (P = 0.07, 4.25 vs. 3.97 cm), also reflected in higher creatinine (P < 0.0001, 3,127 vs. 2,775 ng/mL), which is used to estimate muscle mass. However, 3MH, which is an indicator of muscle mobilization, was also greater (P = 0.03, 431 vs. 356 ng/mL). Disruption of the circadian rhythm during the dry period did not cause increased tissue mobilization and could potentially reduce the amount of muscle mobilization. Regardless of treatment, the extent of both muscle and adipose tissue mobilized during the transition period is substantial.