title: Effects of anabolic implants and ractopamine-HCl on muscle fiber morphometrics, collagen solubility, and tenderness of beef longissimus lumborum steaks.
abstract: The 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: = 33, initial BW 430 ± 7 kg; group 2: = 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; = 21); implant, no ractopamine hydrochloride (IMP; = 22); implant and ractopamine hydrochloride (COMBO; = 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∙d 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 × DOA interaction for WBSF ( = 0.86), but treatment and DOA impacted WBSF ( < 0.01). Over the entire aging study, COMBO steaks had greater ( < 0.01) shear force values when compared to CON steaks. The IMP steaks tended to have decreased ( = 0.07) shear force when compared to the COMBO steaks, but did not differ ( = 0.11) from CON steaks. The IMP and COMBO treatments had increased type IIA fiber CSA when compared to CON ( < 0.01). When compared to each other, the IMP and COMBO type IIA fiber CSA did not differ ( = 0.76). Type I and IIX fiber CSA tended to be greater than CON for IMP and COMBO treatments ( < 0.10). There was no treatment × DOA interaction for all collagen measures ( > 0.33). Collagen amounts were not impacted by GP treatment ( > 0.72), but DOA increased the concentration of soluble collagen ( = 0.04). Fiber CSA of all fiber types were positively correlated ( < 0.05; = 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 ( < 0.10; = -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.
authors.forename: S M
authors.initials: SM
authors.lastname: Ebarb
authors.forename: K J
authors.initials: KJ
authors.lastname: Phelps
authors.forename: J S
authors.initials: JS
authors.lastname: Drouillard
authors.forename: K R
authors.initials: KR
authors.lastname: Maddock-Carlin
authors.forename: M A
authors.initials: MA
authors.lastname: Vaughn
authors.forename: D D
authors.initials: DD
authors.lastname: Burnett
authors.forename: J A
authors.initials: JA
authors.lastname: Noel
authors.forename: C L
authors.initials: CL
authors.lastname: Van Bibber-Krueger
authors.forename: C B
authors.initials: CB
authors.lastname: Paulk
authors.forename: D M
authors.initials: DM
authors.lastname: Grieger
authors.forename: J M
authors.initials: JM
authors.lastname: Gonzalez
mesh_terms: D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D000375:Aging; D000818:Animals; D002417:Cattle / Q000502:physiology*; D003094:Collagen / Q000737:chemistry*; D005260:Female; D018485:Muscle Fibers, Skeletal / Q000187:drug effects*; D010627:Phenethylamines / Q000494:pharmacology*; D000069466:Red Meat / Q000032:analysis*; D012995:Solubility
chemical_list: D000318:Adrenergic beta-Agonists; D010627:Phenethylamines; C060897:ractopamine; D003094:Collagen