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The ontogeny of the somatotropic axis in Hereford calves from birth to one year of age and its response to administration of exogenous bovine somatotropin¹

Department of Animal Science, University of Connecticut, Storrs 06269-4040

³ Correspondence: 3636 Horsebarn Road Ext. (phone: 860-486-0861; fax: 860-486-4375; e-mail: szinn{at}canr.uconn.edu).

Abstract

Administration of exogenous bovine ST (bST) increases growth rate, feed efficiency, and carcass quality in beef cattle. The magnitude of response to bST in beef cattle is variable and related to the age of the animal. Our objective was to determine the response of the somatotropic axis, in particular IGF-I, IGFBP-2, and IGFBP-3, to bST treatment from birth to 1 yr of age. Blood samples were collected before and after a single injection of bST (500 mg) every 50 d from birth to 1 yr of age in male and female Hereford calves. Body weights and serum concentrations of ST, IGF-I, IGFBP-2, and IGFBP-3 were determined. At birth, serum concentrations of ST, IGF-I, and IGFBP-3 increased (P < 0.05) following bST treatment. From 50 to 350 d of age, average concentrations of ST and IGF-I were greater (P < 0.05) in males, whereas IGFBP-2 concentrations were greater (P < 0.05) in females. No gender differences in IGFBP-3 concentrations were observed. Following bST treatment, IGF-I increased (P < 0.05) from 50 to 350 d of age, IGFBP-2 decreased (P < 0.05) from 50 to 200 d of age, and IGFBP-3 increased (P < 0.05) at 250 d of age. At 250 d of age, baseline concentrations of IGFBP-2 decreased (P < 0.05). Due to the positive response of IGFBP-3 and decreased baseline IGFBP-2 at 250 d of age, we conclude that this is an age at which the somatotropic axis is most responsive to exogenous bST, and it therefore may be an appropriate age to begin bST treatment in beef calves to realize the positive influence of bST on BW gain, feed efficiency, and carcass composition.

Key Words: Bovine • Insulin-Like Growth Factor-I • Insulin-Like Growth Factor-Binding Proteins • Somatotropic Axis • Somatotropin

This article has been cited by other articles:

				B. T. Velayudhan, K. E. Govoni, T. A. Hoagland, and S. A. Zinn Growth rate and changes of the somatotropic axis in beef cattle administered exogenous bovine somatotropin beginning at two hundred, two hundred fifty, and three hundred days of age J Anim Sci, November 1, 2007; 85(11): 2866 - 2872. [Abstract] [Full Text] [PDF]