Metabolic Hormone Profiles and Evaluation of Associations of Metabolic Hormones with Body Fat and Reproductive Characteristics of Angus, Brangus, and Brahman Heifers1

Metabolic hormone profiles and their associations with measures of body fat and reproduction were evaluated among Angus, Brangus, and Brahman heifers (n = 8/breed). Heifers of similar age from breeding programs in semi-arid environments were pen-fed for 10 wk prior totheir yearling breeding season. At the beginning of this 10-wk period, heifers were 317 ± 8.6 d of age. Subsequently, heifers were exposed to breeding for 12 wk as they grazed the Chihuahuan Desert. Despite greater (P < 0.05) ADG in Angus heifers than in Brahman heifers, hip height was greater (P < 0.05) in Brahman heifers than in Angus or Brangus heifers at the end of the 10-wk period. Puberty occurred 40.5 d earlier (P < 0.05) in Angus heifers than in Brangus heifers, but was undetected in Brahman heifers of these ages. Serum concentrations of leptin were positively associated (r ≥ 0.27, P ≤ 0.05) with measures of body fat across breed groups. Concentrations of this hormone during wk 4 to 10 were greater (P < 0.05) in Angus than in Brangus, and greater in Brangus than in Brahman heifers. Conversely, serum concentrations of IGF-I were greater (P < 0.05) in Brangus and Brahman heifers than Angus heifers during the 10 wk. Serum concentrations of glucose, insulin, leptin, growth hormone, and insulin-like growth factor-I determined at the end of the 10-wk period were not significant predictors of growth or reproductive traits. Results provide evidence to suggest that growth and reproductive observations herein were typical of Angus, Brangus, and Brahman heifers. Novel results from the study suggest differences exist among these breeds in serum concentrations of leptin and insulin-like growth factor-I in similar-age comparisons.