title: Effect of ractopamine-hydrochloride and trenbolone acetate on longissimus muscle fiber area, diameter, and satellite cell numbers in cull beef cows.
abstract: The objective of this study was to evaluate the effects of coadministration of ractopamine-HCl (RAC) and trenbolone acetate plus estradiol (TBA) on LM fiber cross-sectional area (CSA), diameter, fiber-associated myonuclei, and satellite cell number. Culled crossbred beef cows (n = 98; 11 +/- 1.8 yr old; 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 on arrival into light (initial BW = 369.75 +/- 2.68 kg and end BW = 501.96 +/- 6.90 kg) and heavy (initial BW = 418.31 +/- 2.75 kg and end BW = 522.15 +/- 7.09 kg) groups before assignment to treatment. Factors included dietary treatment (0 or 15 ppm) and implant status (0 or 80 mg of trenbolone acetate + 16 mg of estradiol). Ractopamine was provided in the diet to 2 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 obtained from 10 randomly selected carcasses from each treatment group (n = 40). Cryosections (12 mum) were immunostained for dystrophin and myosin heavy chain I or II for the measurement of fiber CSA and type, respectively. Fiber-associated nuclei and satellite cell numbers were measured in serial cryosections. There was a RAC x TBA interaction (P < 0.05). 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 fiber-associated nuclei 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.
authors.affiliation: Department of Animal Sciences, University of Florida, Gainesville 32611, USA.
authors.forename: J M
authors.initials: JM
authors.lastname: Gonzalez
authors.forename: J N
authors.initials: JN
authors.lastname: Carter
authors.forename: D D
authors.initials: DD
authors.lastname: Johnson
authors.forename: S E
authors.initials: SE
authors.lastname: Ouellette
authors.forename: S E
authors.initials: SE
authors.lastname: Johnson
mesh_terms: D000318:Adrenergic beta-Agonists / Q000008:administration & dosage / Q000494:pharmacology*; D045930:Anabolic Agents / Q000008:administration & dosage / Q000494:pharmacology*; D000818:Animals; D002417:Cattle / Q000502:physiology*; D002452:Cell Count; D004032:Diet / Q000662:veterinary; D005260:Female; D016018:Least-Squares Analysis; D018485:Muscle Fibers, Skeletal / Q000166:cytology / Q000187:drug effects*; D018482:Muscle, Skeletal / Q000187:drug effects / Q000254:growth & development; D051763:PAX7 Transcription Factor / Q000032:analysis; D010627:Phenethylamines / Q000008:administration & dosage / Q000494:pharmacology*; D011897:Random Allocation; D032496:Satellite Cells, Skeletal Muscle / Q000166:cytology / Q000187:drug effects; D013997:Time Factors; D014204:Trenbolone Acetate / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000494:pharmacology
chemical_list: D000318:Adrenergic beta-Agonists; D045930:Anabolic Agents; D051763:PAX7 Transcription Factor; D010627:Phenethylamines; C060897:ractopamine; D014204:Trenbolone Acetate