ESTRUS, OVULATION, LUTEINIZING HORMONE, AND SUCKLING-INDUCED HORMONESIN 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) mast ectomized + unrestricted calf presence (MCP; n = 7); and 4) udder-inta ct cows + unrestricted calf presence (UICP; n = 8). Except for MCW cow s, 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 UIC P treatments were separated overnight from their dams, and before and upon reunion, blood samples were collected from the cows to assess cha nges in oxytocin, cortisol, and prolactin. Calves in the MCP and UICP treatments attempted to or suckled their dams for a similar duration u pon reunion, respectively. Concentrations of cortisol and percentage o f change in oxytocin and prolactin were increased(P < .05) for up to 1 2 min in MCP cows after reunion with their calves. Average concentrati ons of serum LH in samples collected on d 14, 21, 28, and 35 did not d iffer 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 c oncentrations, and greater (P < .05) average maximum concentrations of LH than UICP cows after d 14. Intervals to first ovulation were simil ar in MCW and MCR cows but shorter (P < .01) than those in MCP and UIC P cows. Attempted suckling of mastectomized dams by their calves was a ssociated with increased serum cortisol and percentage of increase in serum oxytocin and prolactin. Despite increased LH in MCP cows, interv als to first ovulation did not differ from those of UICP cows.