Effects of heifer finishing implants on beef carcass traits and longissimus tenderness1

Cattle production practices and the incidence of dark cutting beef

The effects of cattle sex, production system, growth promotant use, slaughter season, carcass phenotype, and pre-slaughter cattle management on the incidence of beef carcasses grading Canada B4 (dark cutting) were investigated using two data sets (A, n = 2009, and B, n = 86,408) containing data from cattle that produced Canada Prime, AAA, AA, A, and B4 carcasses. The probability of producing a Canada B4 carcass was greater (P < .0001) for heifers than steers in both data sets, with the likelihood of dark cutting decreasing with increased carcass weight in heifers in data set B. The incidence of dark cutting was increased (P < .0001) in Winter-born calf-fed (WC) and Fall-born calf-fed (FC) heifers. Production system and phenotype appear to interact to influence the incidence of dark cutting.

TMT-Based Proteomics Profiling of Bovine Liver Underscores Protein Markers of Anabolic Treatments

Illegal use of growth promoter compounds in food production exposes consumers to health risk. Surveillance of such practices is based on direct detection of drugs or related metabolites by HPLC-MS/MS. Screening strategies focusing on indirect biological responses are considered promising tools to improve surveillance. In this study, an untargeted shotgun proteomics approach based on tandem mass tags (TMTs) is carried out to identify proteins altered in bovine liver after different anabolic treatments. Three controlled pharmacological treatments with dexamethasone, a combination of dexamethasone and clenbuterol, or a combination of sexual steroids (trenbolone and estradiol) are analyzed. Untargeted TMT analysis of liver digests by high resolution MS allowed for the relative quantification of proteins. Thanks to partial least squarediscriminant analysis, a set of proteins capable to classify animals treated with dexamethasone alone (11 proteins), or in combination with clenbuterol (13 proteins) are identified. No significant difference is found upon administration of sexual steroids. After relative quantification of candidate markers by parallel reaction monitoring (PRM), two predictive models are trained to validate protein markers. Finally, an independent animal set of control bulls and bulls treated with dexamethasone is analyzed by PRM to further validate a predictive model giving an accuracy of 100%.

The impact of two different hormonal growth promotants (HGPs) on the eating quality of feedlot-finished steer carcasses

The Meat Standards Australia beef-grading model applies a variable adjustment for different cuts of hormonal growth promotant (HGP)-treated carcasses, but does not differentiate between different HGP types. Using 300 non-implanted Bos indicus–Bos taurus composite steers, an experiment was conducted to compare the effects of an oestradiol only (OES) and a combination trenbolone acetate and oestradiol (TBA+OES) implant with non-implanted animals (CON) fed a concentrate ration for 73 days before slaughter, on eating quality of the mm. longissimus lumborum (LL) and gluteus medius (GM) muscles. Sensory and objective LL and GM samples were aged for either 5 or 35 days before freezing at −20°C. Carcass weights from each group were significantly (P &lt; 0.05) different. Corrected for carcass weight, HGP treatment had a significant effect on hump height, ossification score, marble score, P8 fat depth and eye-muscle area. The TBA+OES treatment resulted in significantly (P &lt; 0.05) tougher meat than the OES and CON treatments as assessed by shear force, although this difference was reduced with aging. Sensory scores (tenderness, juiciness, like flavour, overall liking and a composite MQ4 score) confirmed a negative HGP treatment effect, whereby TBA+OES was significantly lower than the CON and OES treatments after 5 days of aging, and these differences were reduced through aging. TBA+OES had a greater impact on sensory scores in the LL when compared to the GM. Both HGP treatments increased calpastatin activity, and the TBA+OES treatment was significantly (P &lt; 0.05) different from the CON and OES treatments. It was concluded that OES and TBA+OES implants have different impacts on meat eating-quality measurements, which could have important implications for the Australian and international beef industry.

Effects of hormonal growth promotants on beef quality: a meta-analysis

Benefits of hormonal growth promotants (HGPs) include production efficiency, profit, and reduced environmental effects for beef cattle. Questions remain about effects of HGP on beef quality, particularly on measures of toughness such as Warner-Bratzler shear force (WBSF), tenderness, and other taste-panel attributes of beef. The objective of this meta-analysis was to assess the effects of HGP on beef quality using the results of randomized controlled trials identified from 3 searched databases. Thirty-one experiments with 181 treatment comparisons were used to evaluate the effects of HGP on WBSF and sensory measures of beef quality. Experiments varied in design, used many different hormonal treatments and combinations, which were single or repeated, in different breeds and sex groups of cattle, with or without electrical stimulation, and with different lengths of time on feed and beef aging. The effects of multiple treatment comparisons in experiments were evaluated using robust regression models and compared to Knapp-Hartung and permutation meta-analytical methods. Increased WBSF was associated with HGP treatment. Use of multiple HGP implants was associated with an increase in WBSF of 0.248 kg (95% CI = 0.203 to 0.292). Effects of a single implant only increased WBSF by 0.176 kg (95% CI = 0.109 to 0.242). Aging of beef did not alter the association of HGP with increased WBSF (P = 0.105); however, the point direction was toward a reduced effect with aging (standardized mean difference [SMD] = -0.005 per day aged). While aging lowered WBSF, it did not reduce the SMD between HGP treatment and reference groups. Comparisons using trenbolone acetate did not differ in WBSF from those using other implants (P > 0.15). The findings on sensory panel tenderness differ from those using WBSF as HGP treatment was not associated with reduced tenderness (P > 0.3) and multiple HGP treatments improved tenderness (SMD = 0.468) compared to a single implant. Further, juiciness, flavor, and connective tissue were not associated with HGP use, whereas there was a marked 5.5-point decrease in the Meat Standards Australia meat quality 4 score, albeit with limited experiments. In general, the true variance of experiments, tau2 (τ2) was low (<0.1), but heterogeneity, I2 was high (>50%) indicating that much of the variance was due to factors other than measurement error. More targeted studies on the role of HGP in influencing beef quality are needed.

Effects of hormonal growth promotants on beef quality: a meta-analysis

Benefits of hormonal growth promotants (HGPs) include production efficiency, profit, and reduced environmental effects for beef cattle. Questions remain about effects of HGP on beef quality, particularly on measures of toughness such as Warner-Bratzler shear force (WBSF), tenderness, and other taste-panel attributes of beef. The objective of this meta-analysis was to assess the effects of HGP on beef quality using the results of randomized controlled trials identified from 3 searched databases. Thirty-one experiments with 181 treatment comparisons were used to evaluate the effects of HGP on WBSF and sensory measures of beef quality. Experiments varied in design, used many different hormonal treatments and combinations, which were single or repeated, in different breeds and sex groups of cattle, with or without electrical stimulation, and with different lengths of time on feed and beef aging. The effects of multiple treatment comparisons in experiments were evaluated using robust regression models and compared to Knapp-Hartung and permutation meta-analytical methods. Increased WBSF was associated with HGP treatment. Use of multiple HGP implants was associated with an increase in WBSF of 0.248 kg (95% CI = 0.203 to 0.292). Effects of a single implant only increased WBSF by 0.176 kg (95% CI = 0.109 to 0.242). Aging of beef did not alter the association of HGP with increased WBSF (P = 0.105); however, the point direction was toward a reduced effect with aging (standardized mean difference [SMD] = -0.005 per day aged). While aging lowered WBSF, it did not reduce the SMD between HGP treatment and reference groups. Comparisons using trenbolone acetate did not differ in WBSF from those using other implants (P > 0.15). The findings on sensory panel tenderness differ from those using WBSF as HGP treatment was not associated with reduced tenderness (P > 0.3) and multiple HGP treatments improved tenderness (SMD = 0.468) compared to a single implant. Further, juiciness, flavor, and connective tissue were not associated with HGP use, whereas there was a marked 5.5-point decrease in the Meat Standards Australia meat quality 4 score, albeit with limited experiments. In general, the true variance of experiments, tau2 (τ2) was low (<0.1), but heterogeneity, I2 was high (>50%) indicating that much of the variance was due to factors other than measurement error. More targeted studies on the role of HGP in influencing beef quality are needed.

Urinary Concentrations of Steroids in Bulls under Anabolic Treatment by Revalor-XS® Implant

Despite the European ban of using anabolics in food-producing animals, growth promoters might still be illegally used in the European Union. To control the food chain and guarantee consumers' health, there is a need of highly sensitive analytical methods for the identification of marker residues of such treatments. In the present study, a group of bulls (n = 16) received trenbolone acetate (200 mg) and estradiol (40 mg) by a commercial ear implant during a time range of 71 days, and a second group (n = 16) was kept for control. The aim of the research was to measure the residual urinary concentrations of the administered drugs (β-trenbolone and β-estradiol), their main metabolites (α-trenbolone and α-estradiol), and possible alterations of the urinary profile of other endogenous hormones metabolically related. The analytical method was based on liquid chromatography-tandem mass spectrometry. Results showed average urinary concentrations of α-trenbolone and α-estradiol during treatment in the range of (0.81 ÷ 2.1) ng mL^-1 and (0.96 ÷ 4.4) ng mL^-1, respectively, whereas β-trenbolone and β-estradiol exhibit urinary concentrations lower than 0.22 ng mL^-1 in both cases. Data obtained from the urinary profiles of endogenous steroids indicate that they could be useful to indirectly detect the ongoing treatment.

Beef quality traits of heifer in comparison with steer, bull and cow at various feeding environments

The present review has been focused largely on the sex type differences in beef quality among heifers, cows, steers and bulls in various feeding environments. Genetic groups, feeding systems and gender are the major factors that change carcass characteristics and fatty acid profiles of cattle. Studies identified that heifer beef has super characteristics in eating quality and a better healthy composition in fatty acids than steer, cow and bull. Diet influences the variation of fatty acid profile; particularly the level of polyunsaturated fatty acids (PUFA) interacts with breed and sex. Animals finished in pasture systems were reported to show better ratios of PUFA/ saturated fatty acids and n-6/n-3. Carcasses of roughage-fed beef are lighter and have less marbling and lower quality grades but have higher cutability than carcasses of grain-fed bulls. Heifers and cows are reported to deposit more fat than steers and bulls. Among males, lower production of testosterone by steers favors more fat thickness compared with bulls. Marbling greatly varies among cattle belonging to different sexes, and particularly, females have genetic makeup that efficiently controls deposition. The current review identified that heifers can be a premium beef brand, while steer beef currently take a large part of market share across the world.

High-dose anabolic implants are not all the same for growth and carcass traits of feedlot steers: a meta-analysis

A meta-analysis of studies evaluating feedlot steer implant programs was conducted to evaluate the differential effects of anabolic implant dosage on feedlot performance and carcass traits. The effect sizes of the implant dosage of interest vs. negative controls and vs. other implant dosages on various dependent variables (ADG, F:G, DMI, dressing percentage [DP], HCW, yield grade, percentage Choice or higher, and marbling score) were calculated. Treatments used for comparisons included no implant, EST (20 mg estradiol benzoate + 200 mg progesterone, 36 mg zeranol, or 72 mg zeranol), ET120 (24 mg estradiol 17β + 120 mg trenbolone acetate [TBA]), and ET200 (28 mg estradiol benzoate + 200 mg TBA or 20 mg estradiol-17β + 200 mg TBA). In the first analysis, the 3 implant dosages were compared to negative control. A second analysis was conducted to compare ET120 vs. ET200 using only studies that included a direct comparison of these 2 dosages. The number of studies included in the analysis for each implant dosage and response variable ranged from 34 to 7. A mixed model was used to evaluate individual implant treatments; implant dosage was a fixed effect, and individual study was included as a random effect. All dosages had greater ADG, DMI, and HCW and lower F:G, percentage Choice, and marbling score vs. negative controls (P < 0.05) In the second direct comparison analysis, ET200 tended to have greater ADG (P = 0.10) and HCW (P = 0.07) and had lower F:G (P < 0.01) and percentage of carcasses grading Choice or greater (P < 0.01) vs. ET120. Differences in HCW between ET120 and ET200 diminished numerically with increasing days of implant activity (P < 0.01). All dosages of implants evaluated herein increased performance and decreased quality grade vs. negative controls. Combination implants containing estrogen (E) and 200 mg TBA have greater potency for growth promotion than implants containing E+120 mg TBA resulting in slightly greater performance.

MEAT SCIENCE AND MUSCLE BIOLOGY SYMPOSIUM--implant and beta agonist impacts on beef palatability

The use of anabolic implants has a long-standing place in the cattle feeding industry, due to their positive impact on growth performance and subsequent profitability. However, implants can have adverse effects on carcass quality, shear force, and eating quality depending on the dose and frequency, or what some refer to as the aggressiveness of the implant regimen administered. Within the past decade, a new class of growth promotants, known as β-adrenergic agonists (βAA), has emerged in the beef feeding industry in the United States. Currently, 2 have gained U.S. Food and Drug Administration approval for use in beef finishing diets to improve performance and carcass yields. Much like anabolic implants, these repartitioning agents can have negative effects on Warner-Bratzler shear force (WBSF), but the differences do not necessarily translate directly to consumer responses for palatability and acceptance in some instances, especially when tenderness is managed through proper postmortem aging. As researchers continued to investigate the mechanisms responsible for the impact of βAA, inevitably this led to consideration of the interaction between βAA and anabolic implants. Early work combining zilpaterol hydrochloride (ZH) with anabolic implants improved performance, carcass yield, and meat yield with additive negative effects on WBSF. Similar results were produced when pairing ZH with anabolic steroids equipped with various release patterns. As with any tool, the key to success is proper management. Certain cattle populations may be better suited to receive growth promotants such as implants and βAA, and postmortem management of subprimal cuts becomes vital when producers take more aggressive approaches to improve performance and yield. The objective of this review is to overview research findings related to the impact of growth promotant technologies on beef palatability, focusing specifically on the role of implants and βAA on carcass quality, beef tenderness, and consumer responses for meat palatability.

Effects of estradiol benzoate and trenbolone acetate, alone or in combination at dose levels present in Synovex Choice, on performance by feedlot heifers

Trials were conducted with beef heifers at 4 sites to evaluate feedlot performance and carcass characteristics in response to implants containing 14 mg estradiol benzoate and 100 mg trenbolone acetate (EB/TBA; Synovex Choice, Zoetis LLC, New York, NY), 14 mg estradiol benzoate (EB), 100 mg trenbolone acetate (TBA), or a sham-implanted control (SC). The study design at each site was a randomized complete block with 12 blocks and 4 treatments. Blocks of cattle at each site were harvested in commercial abattoirs when masked personnel estimated at least 60% of animals would yield carcasses with USDA quality grades of Choice or Prime. Data were pooled across sites for statistical analysis. Initial BW averaged 374 kg, and days on feed ranged from 98 to 126 d (mean 112 d). Heifers implanted with EB/TBA, EB, and TBA had greater ADG and G:F (P < 0.05) than SC; ADG and G:F were greater for EB/TBA than EB or TBA (P < 0.05). Heifers treated with TBA had greater G:F than EB (P < 0.05). Feed intake was not affected by treatments. Mean HCW and LM area for EB/TBA were greater than for other treatments (P < 0.05). Mean HCW for TBA was greater than SC (P < 0.05) but not different from EB. Mean LM area for EB and TBA were greater than SC (P < 0.05) but not different from each other. There were no treatment differences (P > 0.05) for KPH, 12th-rib fat thickness, or yield grade. Dressing percent was greater for EB/TBA than SC (P < 0.05) but not different from EB or TBA. Marbling score was decreased by EB/TBA (P < 0.05) compared with other treatments, but no other differences were noted. Despite the effect of EB/TBA on marbling scores, there were no significant (P > 0.05) treatment differences on proportions of carcasses with quality grades ≥ Choice vs. < Choice. With respect to ADG and G:F, implants containing EB, TBA, or EB/TBA produced improved responses over SC. Furthermore, EB/TBA induced greater ADG and G:F responses than EB and TBA. Results confirmed that EB and TBA have additive effects, as evidenced by the observation that calves implanted with EB/TBA had significantly greater ADG and G:F than heifers implanted with either EB or TBA alone or compared with SC heifers.

Synovex Plus implants coated with a polymeric, porous film improve performance of beef steers and heifers fed in confinement for up to 200 days

Synovex Plus (SP) is a product that delivers 28 mg of estradiol benzoate (EB) and 200 mg of trenbolone acetate (TBA). We studied the impact of a polymeric, porous coating on SP implants (CSP) to prolong release of EB and TBA, and stimulate feedlot performance of feedlot cattle for an extended period. In an explant study, 30 steers were implanted with SP in one ear and CSP in the contralateral ear. Cattle (n = 6/d) were necropsied 40, 81, 120, 160, and 200 d after treatment, and remaining EB and TBA were quantified. Linear regression of EB and TBA remaining as a function of time for each treatment were computed. Rates of EB and TBA depletion from SP were -0.1980 (r(2) = 0.9994) and -1.7073 mg/d (r(2) = 0.9644), respectively, and for CSP rates of EB and TBA depletion were -0.1049 (r(2) = 0.9123) and -0.9466 mg/d (r(2) = 0.9297), respectively. The effect of treatment on depletion rates of each analyte were significant (P < 0.05). Data also showed EB and TBA were delivered from CSP at least 200 d but were delivered from SP about 120 d. Multisite trials with beef-type steers (4 sites) and heifers (4 sites) evaluated feedlot performance and carcass characteristics in response to a CSP implant or when sham implanted (SC). A randomized complete block design with 9 blocks and 2 treatments was used per site within animal gender. Across sites, steers (n = 342, BW = 297 kg) were fed finishing rations for 190 to 202 d (mean 198 d) and heifers (n = 342, BW = 289 kg) were fed finishing rations for 191 to 201 d (mean 198 d). Cattle were harvested and carcasses evaluated. Data were pooled across sites within gender for statistical analysis. Steers and heifers treated with CSP yielded greater (P ≤ 0.003) ADG, DMI, and G:F than SC steers and heifers. Mean BW differences between CSP and SC continued to increase throughout the study, indicating CSP stimulated growth of steers and heifers for 198 d. Mean carcass weights of CSP steers (P = 0.005) and heifers (P = 0.004) were greater than those of SP steers and heifers by 26.2 and 20.6 kg, respectively. The LM area was larger (P < 0.001) in CSP steers and heifers than SC cattle. Marbling decreased with CSP treatment (P ≤ 0.031), which caused reductions (P ≤ 0.006) in proportions of carcasses grading Prime or Choice. Evidence from these studies showed that a single administration of CSP increased feedlot cattle performance for at least 198 d, compared with SC, and may reduce the need to reimplant cattle.

Effects of sequential implanting and ractopamine hydrochloride supplementation on carcass characteristics and longissimus muscle tenderness of calf-fed steers and heifers

A 4 × 2 factorial arrangement of treatments (4 growth-enhancement treatments × 2 sex classes) was used to quantify effects of initial implanting (I-implant, d 0), terminal implanting (T-implant, d 63), and feeding ractopamine hydrochloride [RAC, 200 mg/(animal/d)] for the last 28 d on feed on carcass characteristics and LM shear force (WBSF) of calf-fed steers (n = 159) and heifers (n = 132). Growth-enhancement treatments included the following: TRT1, T-implant only; TRT2, I-implant and RAC; TRT3, I-implant and T-implant; TRT4, I-implant, T-implant, and RAC. Growth responses (BW and ADG) were measured in 3 segments of the finishing period: 1) d 0 to 63, 2) d 63 to 28 d before slaughter, and 3) final 28 d. Cattle were slaughtered after 152, 166, or 180 d of finishing; carcass data were collected after a 48-h chill; and LM WBSF was measured at 3, 7, 14, 21, and 28 d postmortem. A priori contrasts were constructed to test effects associated with use vs. exclusion of growth enhancement in each segment of the finishing period. The interaction between sex class and treatment was not significant (P > 0.05) for any trait tested, indicating that the 4 treatments elicited similar effects in both sexes. Initial implanting improved (P < 0.001) ADG from d 0 to 63 by 11.5%, terminal implanting improved (P < 0.001) ADG from d 63 to 28 d before slaughter by 15%, and supplementing twice-implanted cattle with RAC enhanced ADG during the final 28 d of finishing by 12%. Effects of I-implant, T-implant, and RAC resulted in LM area increases of 3 cm(2) (P = 0.015), 6 cm(2) (P < 0.001), and 3 cm(2) (P = 0.011), respectively, and HCW responses of 11 kg (P = 0.011), 16 kg (P = 0.001), and 6 kg (P = 0.195), respectively. Initial implanting resulted in a 20-point reduction (P = 0.097) in marbling, and T-implant reduced marbling by 25 points (P = 0.04), whereas marbling score was unaffected (P = 0.236) by RAC supplementation. Cattle that received only 1 implant (TRT1 and TRT2) produced carcasses with greater (P = 0.026) mean marbling scores and greater (P = 0.01) rates of conformity to beef carcass marketing specifications for HCW, quality grade, yield grade, and LM area than did cattle that were implanted twice (TRT3 and TRT4). Values for LM WBSF were not affected (P > 0.05) by initial or terminal implanting; however, RAC supplementation increased (P = 0.007) mean LM WBSF by 0.23 kg, which translated into a reduction (P = 0.007) in predicted consumer acceptance of LM steaks.

Effects of genetic markers and implant strategy on longissimus and gluteus muscle tenderness of calf-fed steers and heifers

Effects of genotype (GEN) and implant program (IMP) on LM and gluteus muscle (GM) tenderization were investigated using crossbred steer (n = 185) and heifer (n = 158) calves. The 3-marker GeneSTAR Tenderness panel [CAST (calpastatin), CAPN1 316 (µ-calpain), and CAPN1 4751 (µ-calpain)] was used to determine the GEN of each animal (reported as total number of favorable alleles, 0 through 6). Calves were randomly assigned to 1 of 2 IMP, conventional (CNV) or delayed. Cattle in the CNV group were implanted at the beginning of the finishing period with Revalor-IS or Revalor-IH (Intervet Inc., Millsboro, DE), and then reimplanted 59 d later with Revalor-S or Revalor-H (Intervet Inc.). Calves in the delayed group received a single terminal implant (Revalor-S or Revalor-H) administered 45 d after initiation of the finishing period. Warner-Bratzler shear force (WBSF) was measured on LM and GM steaks at 3, 7, 14, 21, and 28 d postmortem. No interactions between the main effects of sex, IMP, or GEN were detected (P > 0.05) for WBSF. An IMP × postmortem aging (age) interaction was detected (P < 0.05) for LM and GM WBSF. For both muscles, steaks from CNV cattle had WBSF values that were approximately 0.2 kg greater (P < 0.05) than the values for steaks from delayed animals, but only during the early postmortem period (3 to 7 d). A linear effect of GEN on WBSF was detected (P < 0.05) for LM and GM steaks. Within each muscle, steaks from cattle with 6 favorable alleles had WBSF values 0.33 kg less than the values for steaks from cattle with 1 favorable allele. The GEN × age interaction was not significant for LM (P = 0.14) or GM (P = 0.20), but a numerical trend was observed for the effect of GEN on WBSF to diminish as age increased. To investigate how genetic markers could be interfaced with current beef carcass quality grading, cattle were sorted into 2 gene marker groups (GMG), ≤3 vs. ≥4 favorable alleles. For both muscles, GMG was effective only at identifying tenderness differences within the Select grade. When aged ≤14 d, Select LM steaks from cattle with ≥4 alleles had smaller (P < 0.05) WBSF values than did LM steaks from animals with ≤3 alleles. Preslaughter factors (sex, IMP, and GMG) controlled in the present study each accounted for less than 7% of the explained variation in tenderness of the test population. Results from this study suggest that the 3 GeneSTAR Tenderness markers were associated with small differences (0.33 kg) in WBSF and may be useful for increasing the consistency of Select beef, but these specific markers accounted for only a minor amount of variation in beef tenderness.

Tissue selectivity and potential clinical applications of trenbolone (17beta-hydroxyestra-4,9,11-trien-3-one): A potent anabolic steroid with reduced androgenic and estrogenic activity

Recently, the development of selective androgen receptor modulators (SARMs) has been suggested as a means of combating the deleterious catabolic effects of hypogonadism, especially in skeletal muscle and bone, without inducing the undesirable androgenic effects (e.g., prostate enlargement and polycythemia) associated with testosterone administration. 17beta-Hydroxyestra-4,9,11-trien-3-one (trenbolone; 17beta-TBOH), a synthetic analog of testosterone, may be capable of inducing SARM-like effects as it binds to androgen receptors (ARs) with approximately three times the affinity of testosterone and has been shown to augment skeletal muscle mass and bone growth and reduce adiposity in a variety of mammalian species. In addition to its direct actions through ARs, 17beta-TBOH may also exert anabolic effects by altering the action of endogenous growth factors or inhibiting the action of glucocorticoids. Compared to testosterone, 17beta-TBOH appears to induce less growth in androgen-sensitive organs which highly express the 5alpha reductase enzyme (e.g., prostate tissue and accessory sex organs). The reduced androgenic effects result from the fact that 17beta-TBOH is metabolized to less potent androgens in vivo; while testosterone undergoes tissue-specific biotransformation to more potent steroids, dihydrotestosterone and 17beta-estradiol, via the 5alpha-reductase and aromatase enzymes, respectively. Thus the metabolism of 17beta-TBOH provides a basis for future research evaluating its safety and efficacy as a means of combating muscle and bone wasting conditions, obesity, and/or androgen insensitivity syndromes in humans, similar to that of other SARMs which are currently in development.

Hormonal growth promotant use in the Australian beef industry

This review focuses on the science that underpins the use of hormonal growth promotants by Australian beef producers. Their effect on increased liveweight gain is reliable and they are used in the grass-fed industry to produce heavier carcasses suitable for the liveweight and age specifications on high value markets. With implants containing only oestradiol, the growth rate response varies between 0.05 and 0.1 kg/day, dependent on the digestible energy intake and the duration of the implant’s functional life for which the animal is in positive energy balance. Combination implants containing both oestradiol and trenbolone acetate promote greater responses in liveweight gain, which can be as high as 0.2 kg/day on good quality pasture. Although there is also accelerated liveweight gain on energy-dense feedlot diets, the main commercial benefit is reduced feed costs associated with improvements in feed conversion efficiency. An example given demonstrates that finishing an implanted steer from 400 to 650 kg reduces feed consumed by ~4%. Androgenic hormones (testosterone and trenbolone acetate) directly reduce fat content of the carcass. Oestradiol treatment increases mature body size so at any intermediate bodyweight the animal is less mature and likely to have less fat in the carcass. Hormonal treatment has a negative influence on the tenderness and eating quality of beef, the effect being more pronounced with combination implants than with oestradiol alone. Aging for up to 28 days of those muscles that age extensively helps to overcome the detrimental hormonal growth promotant effect.

Growth implants reduced tenderness of steaks from steers and heifers with different genetic potentials for growth and marbling

The objective of this study was to evaluate the effect of growth implants on the carcass characteristics and tenderness of steers and heifers with different genetic potentials for growth, lean meat yield production, and marbling. Two experiments were conducted. Experiment 1 evaluated Angus steers sired by bulls with high EPD for retail product yield or marbling. Implant treatment was imposed randomly within sire groups. Loins (Institutional Meat Purchasing Specifications 180) were collected from each carcass and cut into three 2.54-cm steaks aged for 7, 14 and 21 d to evaluate tenderness. The second experiment evaluated steers and heifers of British and Continental breed descent. Steers and heifers were slaughtered after 120 d on feed. Loin sections were collected, and one 2.54-cm steak aged 7 d was used for tenderness analysis. When implants were used in Angus steers, HCW and LM area increased, whereas internal fat and marbling decreased (P < 0.01). In Angus steers, sire type did not affect shear force values of steaks; however, implant use significantly increased shear force values (P < 0.01). Carcasses from cattle of Continental breed descent were significantly heavier than carcasses of British breed descent with larger LM area, slightly less fat, and a reduced yield grade (P < 0.01). Also, steer carcasses were heavier than heifer carcasses with larger LM (P < 0.05), but no effect of sex on fat depth, internal fat, yield grade or marbling was observed. No significant interactions were seen between growth implant and breed or between growth implant and sex for shear force values. Shear force values were significantly less for steaks from steers and heifers of British decent compared with steers and heifers of Continental descent (P < 0.01). Steaks from implanted steers and heifers had significantly (P < 0.01) greater shear force values than steaks from steers and heifers not implanted. Use of growth implants in growing cattle resulted in significantly heavier carcass weights, larger LM area, and reduced internal fat. However, implant use also reduced the amount of marbling along with contributing to reduced tenderness. Complicating the tenderness issue is the increased shear force values reported for heifers as well as steers of Continental breed descent. Use of implants may contribute to tenderness variability because of different animal responses to implants.