Tenderness is the most important factor that consumers evaluate when determining the acceptability of their beef eating experience. Additionally, consumers are generally willing to pay more for beef that is guaranteed tender. While the beef industry has taken large leaps to explore the mechanisms of tenderness, and used this knowledge to improve the quality of their products, the more widespread use of growth promotion technologies has become a research need due to its potential impact on meat tenderness. Previous literature has documented the negative effects that implants and beta-agonists can have on cooked meat tenderness. Recently, this issue has been pushed to the forefront as new growth promotants available for commercial use have been shown to impact tenderness in a negative fashion. Literature suggests that the negative effects of growth promotants can be mitigated with extended aging periods. However, the industry is still concerned that aging may not completely alleviate tenderness issues seen in animals treated with some growth promotant technologies.
The objective of this study was to evaluate the biochemical and molecular mechanisms that affect tenderness due to the feeding of growth promoting technologies in hopes of developing strategies to counteract such tenderness challenges.
Crossbred feedlot steers (n = 33) were randomly assigned to one of three treatments: control (CON), no implant or Ractopamine hydrochloride (RH); implant, no RH (IMP); and implant and RH (OPT). On day 0 of the study, animals designated to receive anabolic implants were administered Component TE-200 (Elanco Animal Health, Greenfield, IN). Ractopamine hydrochloride (RH) (Optaflexx, Elanco, Greenfield, IN) was included in the total mixed ration of OPT animals with a dietary concentration of 40 mg·day-1·steer-1, for 42 days before harvest.
On day 75, heifers were shipped to a commercial harvest facility (Tyson Fresh Meats, Holcomb, KS). Final body weight, hot carcass weight (HCW), marbling score, loin muscle area (LMA), 12th rib subcutaneous backfat thickness and percent kidney, pelvic and heart fat (KPH) were measured. Strip Loins were removed from one side of each carcass and were transported back to the Kansas State University Meat Laboratory.
72 hours postmortem, one 1.27-cm thick steak was cut from the anterior portion of each Strip Loin and designated for immunohistochemistry and pH was measured. The remainder of the Strip Loin was fabricated into three 3.81-cm thick portions and randomly assigned to an aging period (3, 14 or 21 days). After aging, two, 0.64-cm thick steaks were cut and used for collagen analysis, while the remainder was used to measure Warner-Bratzler shear force.
Growth promotant treatment did not affect dry matter intake, average daily gain or final body weight when comparing any treatment (P > 0.05). Gain to feed ratio (P = 0.06) and dressing percentage (P = 0.07) tended to be affected by growth promotant treatment. Growth promotant technologies in previous literature have elicited drastic improvements in these measurements, which disagrees with this study’s findings. When compared to non-implanted controls, implant regimens have been found to increase average daily gain and gain to feed ratios. Furthermore, the addition of ZH to feedlot diets has been found to increase average daily gain and gain to feed ratio by up to 18% and 25%, respectively. In the current study, combining the implant regimen with ZH did not improve live performance of the heifers during the trial, but did impact some carcass traits. The treatments of IMP and ZIL had greater hot carcass weights, larger ribeye areas and less 12th rib backfat than the CON treatment (P < 0.05). Previous studies have documented that ribeye area increased when animals were fed ZH when compared to animals that were a part of the IMP treatment. Whereas in the current study, there was no difference between the IMP and ZIL treatment for any of these traits.
Previous literature would indicate that employing an implant strategy similar to the current study would have an impact on tenderness. In the current study, the IMP treatment produced steaks that were more tough than CON steaks with 3 days of postmortem aging; however, by 14 days of aging, IMP shear force values were similar to those of the CON treatment. Previous studies have shown that ZH has a substantial impact on objective tenderness measurements. Steaks from the ZIL treatment had greater WBSF values when compared to IMP and CON treatments through 14 days of age, but had similar values to IMP and CON treatments by 21 days of age. These findings suggest that challenges in tenderness due to using growth promoting technologies may be alleviated by extended product aging.
Cross sectional area (CSA) of muscle fibers were measured and CSA was found to be correlated to WBSF values (R>.0.5, P < 0.05). Correlation diminished as days of aging increased. CSA was increased due to treatment: IMP > ZIL > CON (P < 0.05). Total collagen content was not affected by days of age, growth promotant treatment, or location within the steak; however, collagen solubility was affected by aging.
Crossbred feedlot steers (n = 33) were randomly assigned to one of three treatments: control (CON), no implant or Ractopamine hydrochloride (RH); implant, no RH (IMP); and implant and RH (OPT). On day 0 of the study, animals designated to receive anabolic implants were administered Component TE-200 (Elanco Animal Health, Greenfield, IN). Ractopamine hydrochloride (RH) (Optaflexx, Elanco, Greenfield, IN) was included in the total mixed ration of OPT animals with a dietary concentration of 40 mg·day-1·steer-1, for 42 days before harvest.
Animals were harvested at National Beef in Dodge City, KS, allowed to chill for 24 hours and then yield and quality graded by trained personel. Strip Loins were collected and transported to the Kansas State University Meat Laboratory for further fabrication. Strip Loins were fabricated into 3.81-cm thick portions and assigned randomly to aging period (3, 7, 14, 21 and 35 days). Samples were analyzed for WBSF, collagen solubility and calpain activity.
Dry matter intake was not affected by treatment (P > 0.05), and average daily gain only tended (P = 0.09) to be influenced by treatment. Final body weight and gain to feed ratio were affected by treatment (P ≤ 0.05). For both characteristics, the IMP treatment had greater values than the CON treatment, but was not different than the OPT treatment. Furthermore, the OPT treatment did not differ from the CON treatment (P > 0.05). Treatment did not affect hot carcass weight, ribeye area, marbling score, 12th rib backfat thickness, or dressing percentage (P >0.05). These results are in contrast to previous studies, which report higher growth characteristics when feeding RH. The cattle in this study were fed very low levels of RH, which may account for the lack of improvements in growth characteristics.
On days 2 and 35 of aging, all treatments had similar Warner-Bratzler shear force values (P > 0.05). However, on days 7, 14 and 21 of aging, the OPT treatment showed significantly higher (more tough) shear force values when compared to the CON treatment. These findings agree with previous studies that also found that supplementation of RH increased mechanical tenderness measurements. However, similar to Study 1, extended aging periods seemed to alleviate tenderness differences between treatments.
Cross sectional area for Type I and Type IIA muscle fibers was greater for the IMP treatment when compared to the CON or OPT treatments (P < 0.05). The CSA was not higher for OPT treated cattle as expected. This may be due to the low level of RH fed during this study. Treatment also affected µ-calpain levels over the aging period. Muscle from the IMP cattle had a greater amount of intact µ-calpain over the aging periods, which may indicate an increase in action. This may explain why IMP steaks reached similar objective tenderness values as CON as soon as day 14 of aging. The addition of RH at a low level initiated increased amounts of insoluble and total collagen. This increase in connective tissue could be one of the reasons for higher WBSF values in the OPT treatment.
Two groups of crossbred heifers (n = 65) were blocked by weight and assigned to one of three treatments: control (CON) no implant or Ractopamine hydrochloride (RH); implant, no RH (IMP); and Implant and RH (OPT). On day 0 of the study, animals designated to receive anabolic implants were administered Component TE-200 (Elanco Animal Health, Greenfield, IN). Ractopamine hydrochloride (RH) (Optaflexx, Elanco, Greenfield, IN) was included in the total mixed ration of OPT animals with a dietary concentration of 400 mg·day-1·heifer-1, for 28 (group 1) or 29 (group 2) days prior to harvest.
Animals were harvested at Creekstone Farms, Arkansas City, KS, allowed to chill for 48 hours and carcass data was collected using a VBG 2000 Instrument Grading System (E+V Technology GmbH &Co. KG, Oranienburg, Germany). Strip Loins were collected and transported to the Kansas State University Meat Laboratory for further fabrication. Strip Loins were fabricated into 3.81-cm thick portions and assigned randomly to aging period (3, 7, 14, 21 and 35 days). Samples were analyzed for WBSF, collagen solubility, calpain activity and calpastatin activity.
Final body weight, average daily gain, dry matter intake, gain to feed ratio, dressing percentage, yield grade, 12th rib backfat thickness and marbling score did not differ between treatments (P > 0.05). Treatment increased ribeye area of the IMP and OPT treatments compared to the CON treatment (P < 0.05). The lack of treatment effect on live and carcass performance characteristics coincides with results from Study 1, but they both conflict with previously published research documenting growth promoting technology’s effects on animal performance.
The OPT treatment had higher WBSF values than did the CON treatment (P < 0.05), but only tended to have higher values than the IMP treatment (P < 0.07). There were no treatment effects on all collagen attributes measured (P > 0.59), allowing for no logical pattern of collagen alteration to be noted due to the use of growth promotant. There was not an affect of treatment on calpain autolysis, however there was a treatment effect on calpastatin activity (P < 0.05). On day 0 and 2 of aging, the IMP treatment had higher values for calpastatin activity than the CON or OPT treatment. By day 7 of aging, all treatments had similar calpastatin activity (P > 0.05). This finding suggests that growth promoting technologies can slow postmortem degradation through increases in calpastatin activity.
Supplementing beef cattle with a combination of anabolic implants and beta-adrenergic agonists is a common practice employed by producers. These data suggest that differences in the proteolytic calpain system and cross sectional area of muscle fibers contribute to tenderness differences due to growth promotant technologies. Furthermore, it was suggested by the first two studies that extended postmortem aging (greater than 14 days for cattle that were implanted and greater than 21 days for cattle treated with RH and ZH) would help to alleviate the barriers to tenderness caused by growth promotant technologies.