Estrus, ovulation, luteinizing hormone, and suckling-induced hormones in mastectomized cows with and without unrestricted presence of the calf.

Angus x Hereford multiparous cows were assigned to four treatments: 1) mastectomized+calf weaned at birth (MCW; n = 7); 2) mastectomized+calf presence restricted to noninguinal contact (MCR; n = 7); 3) mastectomized+unrestricted calf presence (MCP; n = 7); and 4) udder-intact cows+unrestricted calf presence (UICP; n = 8). Except for MCW cows, cow-calf pairs were penned together individually from parturition (d 0) until d 35 when calves were weaned. On d 7, calves in MCP and UICP treatments were separated overnight from their dams, and before and upon reunion, blood samples were collected from the cows to assess changes in oxytocin, cortisol, and prolactin. Calves in the MCP and UICP treatments attempted to or suckled their dams for a similar duration upon reunion, respectively. Concentrations of cortisol and percentage of change in oxytoxin and prolactin were increased (P < .05) for up to 12 min in MCP cows after reunion with their calves. Average concentrations of serum LH in samples collected on d 14, 21, 28, and 35 did not differ in noncyclic cows among treatments within day postpartum (except for greater [P < .05] LH in MCW cows on d 21). However, MCP cows had more (P < .05) LH pulses (d 21), greater (P < .05) variability in LH pulses (d 21), greater (P < .05) variability in LH concentrations, and greater (P < .05) average maximum concentrations of LH than UICP cows after d 14. Intervals to first ovulation were similar in MCW and MCR cows but shorter (P < .01) than those in MCP and UICP cows. Attempted suckling of mastectomized dams by their calves was associated with increased serum cortisol and percentage of increase in serum oxytocin and prolactin. Despite increased LH in MCP cows, intervals to first ovulation did not differ from those of UICP cows.