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 pos tpartum anovulation, 23 udder-intact cows and their calves were assign ed 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 a nd calf-restricted treatments were weaned after 5 wk. Based on daily m easurements 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 t he calf-present, calf-restricted, and calf-weaned treatments, respecti vely; each one differed (P < .01) from the others. Mean concentrations of LH were greater (P < .05) in the calf-restricted treatment and ten ded (P = .13) to be greater in the calf-weaned treatment than in the c alf-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 darns after overnight separa tion. 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 c ows (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 pres ence without suckling is one factor that delays the onset of first pos tpartum ovulation in beef cows.