Sex effects on plasma leptin concentrations in newborn and postnatal beef calves

Changes in neonatal plasma leptin play a central role in regulating development of the hypothalamic appetite control centers in rodents. In lambs, a postnatal leptin surge has just been reported, and maternal obesity induced by overfeeding initiated before conception and continued throughout gestation blocks this leptin surge in newborn lambs. To investigate the presence, timing, and duration of neonatal leptin profiles, nulliparous cows carrying bull (n = 6) and heifer (n = 6) calves were selected. Cows exhibited no complications during parturition and received no assistance during delivery were chosen for this experiment. A blood sample from the jugular vein was obtained within 2 h of birth, then daily until d 8, and then every other day until d 18 of age at 0700 h. Plasma was collected and analyzed for glucose, insulin, cortisol, and leptin concentrations via validated colorimetric and radioimmunoassay procedures. Plasma hormone and metabolite values were analyzed as repeated measures. Bull calves exhibited elevated plasma leptin concentrations compared with heifers (P = 0.01). Furthermore, plasma leptin concentrations increased from birth until d 2 and then decreased until d 16 of age (P < 0.01). Plasma cortisol was elevated (P < 0.01) at birth and then decreased over the next 5 d. Bull calves had greater (P = 0.04) plasma insulin than did heifer calves. We conclude that there is a postnatal change in plasma leptin with differences due to calf sex and may affect the appetite centers of the hypothalamus influencing appetite and BW gain.