Differing planes of pre- and postweaning phase nutrition in Holstein heifers: II. Effects on circulating leptin, luteinizing hormone, and age at puberty.

The objectives were to investigate the effects of differing planes of pre- and postweaning nutrition on prepubertal serum leptin concentrations, LH profiles, and age at puberty in Holstein heifers. Thirty-six Holstein calves were randomly assigned to either a low (5 L) or high (10 L of whole milk/d) preweaning plane of nutrition from 1 to 7 wk of age, a transition diet (a dry total mixed ration with 85% of concentrate) from wk 8 to 10, and to either a low (70%) or high (85% of concentrate dry total mixed ration) postweaning plane from 11 to 25 wk of age. Serum leptin concentrations were measured every 2 wk from 1 to 25 wk of age, and LH profiles were determined both at wk 15 and 25 based on sequential blood samples taken every 12 min over 10 h. Starting at 26 wk of age, ovaries were examined weekly by transrectal ultrasonography until first ovulation (puberty) was confirmed. Heifers that received the high preweaning plane diet had greater mean (± standard error; SE) leptin concentrations during the preweaning phase than those fed the low plane (2.9 ± 0.1 vs. 2.6 ± 0.1 ng/mL). During the postweaning phase, mean circulating leptin was greater in heifers fed the high compared with the low postweaning diet [3.2 ng/mL (95% confidence interval; CI = 2.7 to 3.4) vs. 2.5 ng/mL (95% CI = 2.3 to 2.8)]. Mean (± SE) amplitude (2.1 ± 0.1 vs. 1.7 ± 0.1 ng/mL), peak (2.2 ± 0.1 vs. 1.8 ± 0.1 ng/mL), and duration (35.6 ± 2.1 vs. 28.7 ± 2.0 min) of LH pulses assessed at wk 15 were greater in heifers offered the high than those offered the low preweaning plane, but no nutritional effects were observed on LH pulses at wk 25. Mean (± SE) age at puberty was 250 ± 9 d and was not influenced by planes of nutrition. However, the likelihood of attaining puberty by 30 wk of age was greater (hazard ratio = 3.8; 95% CI = 1.0 to 14.4) in heifers fed the high postweaning plane compared with the low plane. Heifers achieving puberty by 30 wk also had greater leptin concentrations from wk 1 to 25, whereas for every 1 ng/mL increase in circulating leptin at wk 15 and 25, days to puberty were estimated to decrease by 22 d (95% CI = 1 to 44) and 13 d (95% CI = 1 to 24), respectively. Increasing the preweaning plane from 5 to 10 L/d of whole milk increased serum leptin concentrations at wk 1, 3, and 5 and LH pulse amplitude, peak, and duration at wk 15. Increasing the postweaning plane from 70 to 85% of concentrate resulted in greater circulating leptin concentrations, which may be linked to an earlier onset of puberty.