title: Predicting bull growth performance and carcass composition from growth hormone response to growth hormone-releasing hormone.
abstract: Development of practical, physiologically based methods that provide an early, yet accurate, evaluation of a bull's genetic merit could benefit the beef industry. The use of GH response to a single, acute dose of GHRH was evaluated as a predictor of future growth performance and carcass characteristics of weanling bulls. Fifty-six Angus bulls averaging 229 d (SD = 27) of age were administered three doses i.v. (0, 1.5, and 4.5 microg/100 kg BW) of human GHRH (1-29) analog in a Latin square design balanced for residual effects. Blood samples were collected via jugular catheter at -60, -45, -30, -15, 0, 5, 10, 15, 30, 45, 60, 90 and 120 min relative to GHRH injection. Serum concentrations of GH were plotted over time. Response to GHRH was calculated as the area under the GH response curve (AUC-GH) using the trapezoidal approximation. Relationships between AUC-GH, weaning weight adjusted to 205 d of age (205-d WW), and direct weaning weight EPD (WWEPD) versus age-adjusted BW (BWadj), ADG, and carcass measurements from a 140-d growth performance test were evaluated using simple linear regression. A positive correlation between AUC-GH and ADG and an inverse relationship between AUC-GH and carcass fat were observed. The present study provides evidence that AUC-GH is a better predictor of future growth performance in beef bulls than 205-d WW or WWEPD values. Thus, GH response to GHRH is associated with subsequent growth and may be a useful tool for sire selection in beef production.
authors.affiliation: Department of Animal and Avian Sciences, University of Maryland, College Park 20742-2311, USA.
authors.forename: E E
authors.initials: EE
authors.lastname: Connor
authors.forename: S M
authors.initials: SM
authors.lastname: Barao
authors.forename: L W
authors.initials: LW
authors.lastname: Douglass
authors.forename: S A
authors.initials: SA
authors.lastname: Zinn
authors.forename: G E
authors.initials: GE
authors.lastname: Dahl
mesh_terms: D000818:Animals; D001823:Body Composition; D002417:Cattle / Q000254:growth & development*; D002149:Energy Intake; D013006:Growth Hormone / Q000097:blood*; D013007:Growth Hormone-Releasing Hormone; D006801:Humans; D008297:Male; D010446:Peptide Fragments
chemical_list: D010446:Peptide Fragments; D013006:Growth Hormone; D013007:Growth Hormone-Releasing Hormone; C059148:somatotropin releasing hormone (1-29)