Ebarb, Sara M.Phelps, Kelsey J.Drouillard, James S.Maddock-Carlin, K. R.Vaughn, M. A.Burnett, D. D.Noel, Jere A.Van Bibber-Krueger, Cadra L.Paulk, C. B.Grieger, David M.Gonzalez, John M.2017-11-302017-11-30http://hdl.handle.net/2097/38300Citation: Ebarb, S. M., Phelps, K. J., Drouillard, J. S., Maddock-Carlin, K. R., Vaughn, M. A., Burnett, D. D., . . . Gonzalez, J. M. (2017). Effects of anabolic implants and ractopamine-HCl on muscle fiber morphometrics, collagen solubility, and tenderness of beef longissimus lumborum steaks. Journal of Animal Science, 95(3), 1219-1231. doi:10.2527/jas2016.1263The objective of this study was to examine the effects of growth-promoting technologies (GP) and postmortem aging on longissimus lumborum muscle fiber cross-sectional area (CSA), collagen solubility, and their relationship to meat tenderness. Two groups of black-hided crossbred feedlot heifers (group 1: n = 33, initial BW 430 +/- 7 kg; group 2: n = 32, initial BW 466 +/- 7 kg) were blocked by BW and assigned to 1 of 3 treatments consisting of: no implant and no ractopamine hydrochloride (CON; n = 21); implant, no ractopamine hydrochloride (IMP; n = 22); implant and ractopamine hydrochloride (COMBO; n = 22). Heifers that received an implant were administered an implant containing 200 mg trenbolone acetate and 20 mg estradiol on d 0 of the study, and heifers in the COMBO group received 400 mg.head(-1).d(-1) of ractopamine hydrochloride for 28 (Group 1) or 29 d (Group 2) at the end of 90-(Group 1) or 106-d (Group 2) feeding period. Following harvest, strip loins were collected and further fabricated into 5 roasts for postmortem aging (DOA) periods of 2, 7, 14, 21, or 35 d. After aging, Warner-Bratzler shear force (WBSF), muscle fiber CSA, and collagen solubility were measured. There was no treatment x DOA interaction for WBSF (P = 0.86), but treatment and DOA impacted WBSF (P < 0.01). Over the entire aging study, COMBO steaks had greater (P < 0.01) shear force values when compared to CON steaks. The IMP steaks tended to have decreased (P = 0.07) shear force when compared to the COMBO steaks, but did not differ (P = 0.11) from CON steaks. The IMP and COMBO treatments had increased type IIA fiber CSA when compared to CON (P < 0.01). When compared to each other, the IMP and COMBO type IIA fiber CSA did not differ (P = 0.76). Type I and IIX fiber CSA tended to be greater than CON for IMP and COMBO treatments (P < 0.10). There was no treatment x DOA interaction for all collagen measures (P > 0.33). Collagen amounts were not impacted by GP treatment (P > 0.72), but DOA increased the concentration of soluble collagen (P = 0.04). Fiber CSA of all fiber types were positively correlated (P < 0.05; r = 0.21 to 0.28) with WBSF only on d 2 of aging, while soluble collagen amount tended to negatively correlate with WBSF on d 7 and 14 of aging (P < 0.10; r = -0.24 and -0.23, respectively). Administration of GP during heifer finishing resulted in greater steak WBSF over 35 d of aging, which was not due to collagen characteristics and only minimally affected by fiber CSA.Copyright © 2016. American Society of Animal Science. This Item is protected by copyright and/or related rights. You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s).CollagenExtended AgingImplantsMuscle Fiber TypeRactopamineHydrochlorideArticle