Restricting calf presence without suckling compared with weaning prolongs postpartum anovulation in beef cattle.

To determine how continued presence of a calf affected duration of postpartum anovulation, 23 udder-intact cows and their calves were assigned to three treatments on d 4 to 9 postpartum (experimental d 0). The treatments were 1) calf present with unlimited contact with its dam (n = 8), 2) calf restricted to noninguinal contact with its dam (n = 8), and 3) calf weaned from its dam (n = 7). Calves in the calf-present and calf-restricted treatments were weaned after 5 wk. Based on daily measurements of blood progesterone, days to first ovulation after onset of treatments were 35.4 +/- 2.2, 22.5 +/- 2.2, and 14.3 +/- 2.2 for the calf-present, calf-restricted, and calf-weaned treatments, respectively; each one differed (P < .01) from the others. Mean concentrations of LH were greater (P < .05) in the calf-restricted treatment and tended (P = .13) to be greater in the calf-weaned treatment than in the calf-present treatment on d 7 after the onset of treatments. On d 7 and 21, calves in the calf-present and calf-restricted (calves could not suckle) treatments were returned to their dams after overnight separation. Blood samples were collected to assess changes in cortisol, ACTH, prolactin, and oxytocin. No treatment effects were detected on d 7, but on d 21, the calf-present and calf-restricted cows had a greater (P < .05) increase in cortisol after calf return than the calf-weaned cows (calves were not returned), whereas prolactin was increased (P < .05) after calf return in the calf-present cows only. We conclude that calf presence is associated with an increase in cortisol and calf presence without suckling is one factor that delays the onset of first postpartum ovulation in beef cows.