Effects of growth-promoting implants on morphology of Longissimus and Semitendinosus muscles in finishing steers

• Published in: Meat science 2000-11, Vol.56 (3), p.229-237
• Main Authors: Fritsche, Sonja, Solomon, Morse B., Paroczay, Ernest W., Rumsey, Theron S.
• Format: Article
• Language: English
• Subjects: Anabolic implant; Animal productions; Biological and medical sciences; Biopsy; Biotechnology; Food industries; Fundamental and applied biological sciences. Psychology; Health. Pharmaceutical industry; Hormones. Growth factors; Industrial applications and implications. Economical aspects; Meat and meat product industries; Muscle fiber; Production of active biomolecules; Steer; Terrestrial animal productions; Vertebrates
• ISSN: 0309-1740; 1873-4138
• DOI: 10.1016/S0309-1740(00)00047-4

Growth-promoting implants lead to increased muscle accretion in ruminants. To elucidate the effects at a cellular level, muscle fiber distribution and cross-sectional area (CSA) of longissimus (LM) and semitendinosus (ST) muscles were compared in implanted and control steers. Sixty-four Charolais steers were assigned to one of four treatments (16 steers/treatment): (1) no implant, (2) Synovex-S® (estradiol benzoate+progesterone), (3) Ralgro® (zeranol) or (4) Revalor-S® (trenbolone acetate+estradiol-17β). The experiment was carried out using four slaughter groups (SGRP). Sixteen steers each were slaughtered after 48, 104, 160 and 175 days (four steers/treatment) on trial. Steers on an implant treatment were first implanted at 15 months of age (day 0) and re-implanted at 56 and 112 days. Muscle fibers in the LM and ST (for both live biopsy and post-mortem samples) were characterized as either slow-twitch oxidative (SO), fast-twitch oxidative-glycolytic (FOG) and fast-twitch glycolytic (FG) fibers. Fiber distribution was minimally affected by SGRP in these physiologically mature steers. Implantation with Synovex did not alter fiber distribution in either muscle compared with control steers. Both Synovex-implanted and control steers showed a decrease of FG and an increase of FOG fibers in the LM from day 0 to SGRP 2 followed by an increase of FG and a decrease of FOG fibers. Ralgro- and Revalor-implanted steers had an almost constant fiber distribution in the LM throughout the experiment resulting in higher precentages of FG fibers in SGRP 2 ( P