In postpartum beef cows, variations in luteinizing hormone secretion between suckled and non-suckled cows are not attributable to differences in cortisol secretion, and suckling has no effect on transcortin’s binding capacity or on the concentration of unbound cortisol.

When a calf suckles, nerves from the mother's udder send signals to the brain that directly slow down the release of a hormone that triggers ovulation. This happens without any change in stress hormone levels or how the stress hormone is carried in the blood. When the calf stops suckling, the brain resumes normal hormone pulses, restarting the reproductive cycle.