J. Anim Sci.
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Published online first on April 27, 2007
J. Anim Sci. 1990. doi:10.2527/jas.2006-624
© 2007 American Society of Animal Science
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J. Anim Sci., doi: 10.2527/jas.2006-624
©Copyright, 2007, The American Society of Animal Science

ARTICLE

Effect of ractopamine-HCl and trenbolone acetate on Longissimus muscle fiber area, diameter, and satellite cell numbers in cull beef cows

J. M. Gonzalez 1, J. N. Carter 2, D. D. Johnson 1, S. E. Ouellette 1, S. E. Johnson 1*

1 Department of Animal Sciences, University of Florida, Gainesville, FL 32611
2 North Florida Research and Education Center, Marianna, FL 32446

* To whom correspondence should be addressed. E-mail: sjohnson{at}animal.ufl.edu.


  Abstract

The objective of this study was to evaluate the effects of co-administration of ractopamine-HCl (RAC) and trenbolone acetate plus estradiol (TBA) on LM fiber cross-sectional area (CSA), diameter, fiber-associated myonuclei (FAN), and satellite cell number. Culled crossbred beef cows (n = 98; 11 yr ± 1.8; BCS 4.3 ± 0.03) from a single ranch in south Florida were fed a concentrate diet for 92 d in a 2 x 2 randomized block design. Cows were blocked by BW upon arrival into a light (initial BW = 369.75 ± 2.68 kg; end BW= 501.96 ± 6.90 kg) and heavy (initial BW = 418.31 ± 2.75 kg; end BW= 522.15 ± 7.09 kg) groups before assignment to treatment. Factors included dietary treatment (0, 15 ppm) and implant status (0, 80 mg trenbolone acetate + 16 mg estradiol). Ractopamine was provided in the diet to two pens or half the treatments during the final 35 d of feeding. Cows were slaughtered on d 92. Forty-eight hours postmortem the 6th rib portions of the LM were harvested from 10 randomly selected carcasses from each treatment group (n = 40). Cyrosections (12 µm) were immunostained for dystrophin and myosin heavy chain I or II for the measurement of fiber CSA and type, respectively. Fiber associated nuclei (FAN) and satellite cell numbers were measured in serial cryosections. There was a (P < 0.05) RAC x TBA interaction. Type I fiber CSA and diameter were increased (P < 0.05) by TBA and RAC. Type I CSA and diameter were larger (P < 0.05) in TBA+RAC than RAC only. Type II fiber CSA and diameter were not affected by TBA (P = 0.48), RAC (P = 0.15) or TBA+RAC (P = 0.60). Satellite cell numbers and FAN were not affected (P > 0.05) by implant status or ractopamine supplementation. These results indicate that TBA and RAC preferentially increase the size of type I fibers in cull cows.

Key Words: Beta-agonist, cull cow, muscle fiber, Ractopamine, satellite cell




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S. J. Winterholler, G. L. Parsons, D. K. Walker, M. J. Quinn, J. S. Drouillard, and B. J. Johnson
Effect of feedlot management system on response to ractopamine-HCl in yearling steers
J Anim Sci, September 1, 2008; 86(9): 2401 - 2414.
[Abstract] [Full Text] [PDF]


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Copyright © 2007 by the American Society of Animal Science.