The effect of growth promoting metabolic hormone manipulation on endocrine parameters associated with pubertal development

Puberty is a stage of development that is affected by metabolic and gonadal hormones, body weight, nutrition and total body fat. Manipulation of growth promoting metabolic hormones may influence other endocrine parameters associated with puberty. The objectives for this study were to: 1) evaluate the effect of diet manipulation on growth promoting metabolic hormones during pubertal development and 2) determine a potential mechanistic relationship between metabolic hormones and pubertal gonadal regulators in the brain. Feeding a high energy diet increased body weight at puberty but did not accelerate the onset of puberty in heifers. The diet induced changes on metabolic hormones were not sufficient to influence endocrine parameters or alter age at puberty. Insulin growth factor-I serum concentrations increased in wks 1 and 2 (P≤0.05) in heifers fed a high energy diet (H) compared to control fed heifer (C). However, serum concentrations of GH were higher in C than H heifers as puberty approached. Overall, heifers with an ADG ≥ 0.8 kg/d attained puberty before 1 year of age, independent of dietary treatment. In experiment 2, estrogen receptor (ER) isoforms differed relative to gilt development as puberty approached; specifically, there was a decrease in both ER (ERα and ERβ) isoforms in 16 and 18 week-old-gilts. Moreover, leptin stimulated ERα at -11M dose in 18 week-old-gilts. A similar trend was observed for ERβ but was not significant. In pubertal gilts leptin may stimulate ER expression. Collectively, it can be concluded that metabolic growth promoting hormones are affecting endocrine parameters of pubertal development; however, it appears that metabolic growth hormones may have a permissive influence on age at puberty