Effects of steroidal implantation and ractopamine-HCl on nitrogen retention, blood metabolites and skeletal muscle gene expression in Holstein steers

D. K. Walker, E. C. Titgemeyer, E. K. Sissom, K. R. Brown, J. J. Higgins, G. A. Andrews, B. J. Johnson

Research output: Contribution to journalArticle

15 Scopus citations

Abstract

Six Holstein steers (231 ± 17 kg) housed in metabolism crates were used in a randomized complete block design with three blocks of two steers based on previous serum insulin-like growth factor (IGF)-I concentrations. One of the two steers in each block was implanted with 120 mg trenbolone acetate and 24 mg oestradiol-17β on day 0. None of the steers was fed ractopamine-HCl in the initial 28 days, and then all steers were fed 200 mg of ractopamine-HCl per steer daily from day 28 until the end of the trial. Steers were fed a corn-based diet (62% rolled corn, 20% expeller soya bean meal and 15% alfalfa hay) twice daily with an average dry matter intake of 4.8 kg/day. Blood and M. longissimus biopsy samples were collected prior to implantation and on days 14, 28, 42 and 56. There was an implant × ractopamine interaction for retained nitrogen (p < 0.05); ractopamine feeding led to only small improvements in nitrogen retention for implanted steers (45.9 g/day vs. 44.5 g/day), whereas ractopamine led to larger increases in nitrogen retention for non-implanted steers (39.0 g/day vs. 30.4 g/day). Implantation increased (p < 0.05) and ractopamine tended to decrease (p = 0.06) serum IGF-I concentrations. Implantation tended to increase (p = 0.16) and ractopamine decreased (p < 0.05) mRNA expression of IGF-I in the M. longissimus. Ractopamine decreased mRNA expression of β1- and β2-receptors in M. longissimus (p ≤ 0.02). The steroidal implant and the feeding of ractopamine both increased nitrogen retention in steers, but the combination did not yield an additive response. The two growth promotants had opposite effects on serum concentrations of IGF-I and mRNA expression of IGF-I in M. longissimus.

Original languageEnglish
Pages (from-to)439-447
Number of pages9
JournalJournal of Animal Physiology and Animal Nutrition
Volume91
Issue number9-10
DOIs
StatePublished - Oct 2007

Keywords

  • Cattle
  • Growth
  • Ractopamine
  • Steroidal implant

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