HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) All Versions of this Article: jas.2007-0281v1 85/11/2866    most recent Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Velayudhan, B. T. Articles by Zinn, S. A. Search for Related Content PubMed PubMed Citation Articles by Velayudhan, B. T. Articles by Zinn, S. A.

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 age¹

Department of Animal Science, University of Connecticut, Storrs 06269

⁴ Corresponding author: steven.zinn{at}uconn.edu

To determine the effects of bovine somatotropin (bST) treatment beginning at 3 ages on the growth rate and components of the somatotropic axis, 40 beef cattle (200 ± 21 d of age) were randomly assigned to 1 of 4 treatments (10 animals/treatment). Three of the treatment groups received bST (33 µg/kg of BW) daily beginning at 200, 250, or 300 d of age until all animals reached 400 d of age; the fourth group served as controls (0 bST). Animals were housed in pens (5 animals per pen; 2 pens per treatment) and fed a diet formulated for an ADG of 1.2 kg/d. Feed intake (per pen) was measured daily, and BW was determined weekly. Blood samples (10 mL) and ultrasound measurements were collected at 200, 250, 300, 350, and 400 d of age. Serum concentrations of ST and IGF-I were determined by RIA and IGFBP-2 and -3 by ligand blot procedures. Overall, cattle gained 284.0 ± 14.7 kg of BW with a treatment x week interaction (P < 0.01), such that during the treatment period ADG was 11.6, 8.7, and 15.8% greater (P < 0.05) in cattle treated with bST beginning at 200, 250, and 300 d, respectively, relative to controls during the same time frame. Average DMI was 13.6% less (P < 0.05) in bST-treated cattle than in controls. Increases in ADG coupled with a reduction in DMI resulted in 11.7, 14.0, and 26.4% increases (P < 0.01) in the efficiency of gain (G:F) in bST-treated cattle beginning at 200, 250, and 300 d of age, respectively, compared with contemporary controls. Backfat thickness increased (P < 0.05) over time, but the magnitude of the increase was less in the bST-treated cattle (treatment x week interaction; P < 0.05). Area of the LM increased (P < 0.05) over time but was similar across treatment groups. Serum concentrations of ST, IGF-I, and IGFBP-3 increased (P < 0.05), whereas IGFBP-2 decreased (P < 0.05) over time. The changes in the components of somatotropic axis were more pronounced in bST-treated cattle compared with controls, with the greatest magnitude of response in animals that began bST treatment at 300 d of age. In conclusion, the exogenous bST-induced growth response was greater in animals that began to receive bST administration at 300 d of age and received it for a shorter period (100 d) compared with animals that received bST beginning at 200 or 250 d of age.

Key Words: age • beef cattle • growth rate • insulin-like growth factor • insulin-like growth factor binding protein • somatotropin

This article has been cited by other articles:

				P. M. Yamada and K.-W. Lee Perspectives in mammalian IGFBP-3 biology: local vs. systemic action Am J Physiol Cell Physiol, May 1, 2009; 296(5): C954 - C976. [Abstract] [Full Text] [PDF]