Response to ractopamine-HCl in heifers is altered by implant strategy across days on feed1

Impacts of economic factors influencing net returns of beef feedlot heifers administered two implant programs and fed for differing days-on-feed from pooled randomized controlled trials

The objective of this research was to evaluate the effects of two implant programs and differing days-on-feed (DOF) on net returns of beef feedlot heifers using sensitivity analyses of key economic factors. Crossbred beef heifers [n = 10,583; initial weight 315 kg (± 20.1 SD)] were enrolled across three trials (one Kansas, two Texas feedlot trials). Heifers were blocked by arrival and randomly allocated to one of six pens, resulting in a total of 144 pens and 24 blocks. Pen was randomly assigned to treatment as a 2 × 3 factorial. Implant programs were: IH + 200-Revalor-IH at initial processing, and a terminal implant after approximately 90 DOF (Revalor-200), or, XH-a single implant at initial processing (Revalor-XH). The DOF treatments were: heifers fed to a standard baseline endpoint (BASE) or heifers fed for an additional + 21 or + 42 d beyond BASE. Pen-level partial budgets were used for economic sensitivity analyses, which varied price points of single pricing components with all other components fixed. Variable components were live-fed cattle prices, base carcass prices (i.e., dressed), Choice-Select spread (CS-spread), and feed and yardage prices (FYP). For each, a Low, Mid-Low, Middle, Mid-High, and High price was chosen. Linear mixed models were fit for statistical analyses (α = 0.05). There were no significant two-way interactions (P-values ≥ 0.14). Regardless of the variable component evaluated, XH heifers had poorer net returns than IH + 200 at all prices (P ≤ 0.04). Selling live, the + 21 and (or) + 42 heifers had lower net returns than BASE at every fed cattle price point (P < 0.01). Selling dressed, the + 21 and (or) + 42 heifers had lower returns than BASE at Low, Mid-Low, and Middle fed cattle base prices (P < 0.01); there were no significant DOF differences at Mid-High, or High prices (P ≥ 0.24). Net returns were lower for + 42 than BASE at all CS-spreads (P ≤ 0.03), while BASE and + 21 did not differ significantly. Longer DOF had lower net returns than BASE when selling live at every FYP (P < 0.01) except at the Low price (P = 0.14). Selling dressed, there was no significant effect of DOF at Low or Mid-Low FYP (P ≥ 0.11); conversely, extended DOF had lower net returns than BASE at Middle, Mid-High, and High FYP (P < 0.01). Overall, there was minimal economic evidence to support extending feedlot heifer DOF beyond the BASE endpoint, and when feeding longer, larger reductions in return were observed when marketing live as opposed to dressed.

A randomized trial and multisite pooled trial analyses comparing effects of two hormonal implant programs and differing days-on-feed on carcass characteristics and feedlot performance of beef heifers

Research objectives were to evaluate effects of two implant programs for beef heifers fed three different durations (days-on-feed; DOF) on carcass weight and composition (primary outcomes) and feedlot performance (secondary outcomes) at commercial feedlots. Data from a randomized trial in Kansas were analyzed separately and also pooled with data from two previously published trials conducted in Texas. Heifers were randomly allocated to pens within a block, and pens were randomized to treatments in a 2 × 3 factorial randomized complete block design. Implant programs were IH + 200 - an initial Revalor-IH implant [80 mg trenbolone acetate (TBA) and 8 mg estradiol (E₂)] and a re-implant after a mean of 98-d (± 10.8 SD) with Revalor-200 (200 mg TBA and 20 mg E₂), or XH - Revalor-XH, a single extended-release implant (200 mg TBA and 20 mg E₂). Heifers were fed to a baseline endpoint (BASE; pooled mean 166-d ± 11.9 SD), +21, or +42 additional DOF. A total of 10,583 crossbred heifers with mean initial body weight (BW) 315 kg (± 20.1 SD) were enrolled in 144 pens in 24 blocks (treatment replications) across the three trials. General and generalized linear mixed models accounting for clustering of trials, blocks, and pens were used to test for effects of treatments, with significance set at α = 0.05. The only implant program × DOF interaction in pooled analyses was for dry matter intake (DMI; P < 0.01); IH + 200 heifers had lower mean DMI than XH when fed +42 DOF. Gain:feed was higher for IH + 200 compared to XH with dead and removed animals excluded (P < 0.01) or included (P = 0.03). For IH + 200, hot carcass weight (HCW) increased (P < 0.01), USDA Yield Grade (YG) distributions shifted towards lower numerical categories (P < 0.01), and Prime carcasses decreased while Select increased compared to XH (P < 0.01). For each incremental increase in DOF, final BW (P < 0.01) and HCW increased (P < 0.01), while daily gain (P < 0.01) and gain:feed (P < 0.01) decreased. Categories of YG were affected by DOF (P < 0.01); there were fewer YG 1 and 2 and more YG 4 and 5 carcasses for +42 compared to BASE and +21. USDA Quality Grade (QG) distributions differed by DOF (P < 0.01); each incremental increase in DOF resulted in more Prime and fewer Select carcasses. Without meaningful interactions, tested implant programs likely have a consistent effect when heifers are fed to similar DOF, while changes in HCW, QG, and YG may influence marketing decisions when extending DOF.

Effect of trenbolone acetate, melengestrol acetate, and ractopamine hydrochloride on the growth performance of beef cattle

The effect of trenbolone acetate + estradiol (TBA) implants, melengestrol acetate (MGA), and ractopamine hydrochloride + TBA (RAC + TBA) on growth performance and carcass characteristics in beef cattle (n = 680; 279 ± 10.1 kg) fed barley grain/corn silage was examined in a 4 yr study (four pens per treatment per year; 262 ± 8 d feeding period). In the first 2 yr, treatments were (1) control heifers (H-CON; no growth promoters), (2) TBA-implanted heifers (H-TBA), (3) MGA heifers (H-MGA), (4) control steers (S-CON; no growth promoters), and (5) TBA-implanted steers (S-TBA). A sixth treatment (6) RAC + TBA steers (RAC + TBA) was included in years 3 and 4. Overall dry matter intake (DMI) of heifers was increased (P < 0.001) by TBA but not MGA. Compared with H-CONs, H-TBA had greater average daily gain (ADG) (P < 0.001), gain to feed ratio (G/F) (P < 0.001), and carcass weight (P < 0.001), whereas S-TBA had increased ADG (P < 0.001), G/F (P< 0.001), and carcass weight (P < 0.001) compared with S-CON. Compared with H-CON, H-MGA had increased (P < 0.01) ADG, G/F, and carcass weight. The RAC + TBA had increased (P < 0.01) ADG and carcass weight (3.2%) but not G/F or DMI compared with S-TBA. This 4 yr study showed a consistent positive impact of growth-enhancing technologies on the performance of Canadian feedlot cattle.

Effects of zinc propionate supplementation on growth performance, skeletal muscle fiber, and receptor characteristics in beef steers

A randomized complete block design experiment with 32 yearling crossbred steers (average body weight [BW] = 442 ± 17.0 kg) fed a steam-flaked corn-based diet was used to evaluate the effects of dietary Zn (KemTRACE Zn propionate 27; Kemin Industries, Inc., Des Moines, IA) supplementation on live growth performance, skeletal muscle fiber, and beta-adrenergic receptor (β-AR) characteristics during the finishing phase. Steers were blocked by BW (n = 4 blocks; 8 steers/block), assigned to pens (n = 4 steers/pen), and randomly assigned to the following treatments: control (CON; 0.0 g/[head (hd) · d] of additional Zn) or additional dietary Zn (ZnP; 1.0 g/[hd · d] additional Zn). The basal diet contained Zn (60 ppm dry matter basis) from ZnSO4; additional Zn was top-dressed at feeding. Ractopamine hydrochloride (RH; Optaflexx: Elanco Animal Health, Greenfield, IN) was included at 300 mg/(hd · d) for the final 28 d of the 111-d feeding period. Longissimus muscle biopsy samples, BW, and blood were obtained on days 0, 42, 79, and 107. Final BW was collected prior to shipping on day 111. Biopsy samples were used for immunohistochemical (IHC), mRNA, and protein analysis. Serum urea nitrogen (SUN) and nonesterified fatty acid (NEFA) concentrations were measured. Steers fed ZnP had a greater average daily gain (P = 0.02) and gain to feed ratio (G:F; P = 0.03) during the RH feeding period compared with CON. There were no differences (P > 0.05) in other growth performance variables, carcass traits, mRNA abundance, or relative protein concentration for fiber type and β-AR. Fiber types I and IIA had no differences in the cross-sectional area; however, the IIX area was greater for CON (P < 0.04) compared with ZnP and increased (P < 0.02) over time. There were no differences between treatments for the β1-AR density (P > 0.05) in skeletal muscle tissue throughout the study. A treatment × day interaction was observed in β2-AR density (P = 0.02) and β3-AR density (P = 0.02) during the RH feeding period, where the abundance of the receptors increased with ZnP but did not change in CON. Compared with CON, ZnP had greater (P < 0.01) mean NEFA concentrations. Mean SUN concentrations did increase by day (P < 0.01). Additional dietary Zn, supplied as Zn propionate, upregulates β2-AR and β3-AR and improves growth performance in feedlot steers during the RH feeding period, likely through a shift of resource utilization from lipogenesis to muscle maintenance and hypertrophy.

Effects of a single initial and delayed release implant on arrival compared with a non-coated initial implant and a non-coated terminal implant in heifers fed across various days on feed

Two experiments evaluated the effect of implant number, type, and total steroidal dose on live animal performance and carcass traits in heifers fed for three different days on feed (DOF). In experiment 1, heifers (n = 3,780; 70 heifers/pen and 9 pens/treatment; initial body weight [BW] = 309 kg) were used in a 2 × 3 factorial arrangement of treatments. Factors were as follows: 1) implant (all from Merck Animal Health, De Soto, KS): 200 mg trenbolone acetate (TBA) and 20 mg estradiol-17β (E₂) administered on arrival (SINGLE), or 80 mg TBA and 8 mg E₂ administered on arrival followed by 200 mg TBA and 20 mg E₂ after approximately 90 d (REPEATED) and 2) duration of DOF: harvested after approximately 172, 193, and 214. In experiment 2, heifers (n = 3,719; 65 to 70 heifers/pen and 9 pens/treatment; initial BW = 337 kg) were used with the same factors as experiment 1, except DOF were 150, 171, and 192. No implant × DOF interaction (P ≥ 0.06) was noted for any performance parameters in either experiment. Heifers administered REPEATED had improved (P ≤ 0.05) live gain to feed ratio (G:F) and carcass-adjusted G:F and tended (P = 0.09) to have greater hot carcass weight (HCW) in experiment 1. Increasing DOF resulted in greater (P ≤ 0.01) live and carcass-adjusted final BW and decreased (P = 0.01) live ADG in experiment 1. As DOF increased, HCW, HCW gain, and dressing% (P ≤ 0.01) increased in experiment 1. The mean carcass transfer was 79.6% across the 42 d terminal window in experiment 1. In experiment 2, REPEATED had improved (P = 0.03) carcass-adjusted G:F compared with SINGLE, but HCW was not different (P = 0.36) between treatments. Increased DOF resulted in greater (P ≤ 0.01) final live and carcass-adjusted BW, decreased (P ≤ 0.01) live and carcass-adjusted ADG, and poorer (P ≤ 0.01) live and carcass-adjusted G:F in experiment 2. In experiment 2, dressing percentage was greater (P = 0.02) in REPEATED compared with SINGLE. Heifers given SINGLE had greater (P = 0.01) back fat and estimated empty body fat (EBF), whereas REPEATED had fewer (P = 0.01) Yield Grade 4 carcasses and greater (P = 0.01) longissimus muscle (LM) area. Increased DOF resulted in greater (P ≤ 0.04) HCW, HCW gain, dressing%, back fat, LM area, marbling, EBF%, and United States Department of Agriculture (USDA) Prime-grading carcasses, Yield Grade 4 and 5, and over 454-kg carcasses in experiment 2. Carcass ADG and carcass transfer indicate a 0.70 kg carcass ADG between 150 and 192 DOF, resulting in an average carcass transfer of 72.2% in experiment 2. Although feedlot growth performance and HCW did not differ between the implant regimens tested, increasing DOF resulted in decreased live growth performance while increasing the proportion of USDA prime carcasses and HCW.

Ractopamine Hydrochloride Did Not Impact Carcass Traits, Muscle Fiber Types, or Sensory Traits of Long-Fed Yearling Heifers

Crossbred heifers (n = 64; animal was the experimental unit) were assigned to 1 of 8 treatments in a 4 × 2 factorial arrangement, with 4 treatment days-on-feed (DOF; 79, 100, 121, 142) and 2 levels of ractopamine hydrochloride (RAC) supplementation (0 or 300 mg × hd–1 × d–1). At 24 h postmortem, carcass traits were determined by trained personnel and longissimus samples were removed for muscle fiber type analyses. Boneless strip loins (IMPS #180) were fabricated and vacuum-packaged at 24 h postmortem and aged for 21 d, cut into 2.54 cm thick steaks, then frozen for no longer than 6 mo. After thawing for 24 h, Warner-Bratzler shear force (WBSF) and trained sensory panel analyses were conducted. Marbling was greater (P < 0.05) for control (CON; 0 mg x hd-1 x d-1 ractopamine hydrochloride) heifers than RAC heifers fed for either 79 or 100 d, but lower (P < 0.05) for CON heifers than RAC heifers fed for either 121 or 142 DOF. Feeding RAC had no effect (P > 0.05) on carcass traits, muscle fiber histology, or meat quality. The addition of RAC had no effect (P > 0.05) on Warner-Bratzler shear force. Feeding RAC had no negative impacts on carcass traits or meat quality and actually improved marbling scores in longer-fed heifers.

A meta-analysis of zilpaterol and ractopamine effects on feedlot performance, carcass traits and shear strength of meat in cattle

This study is a meta-analysis of the effects of the beta-agonists zilpaterol hydrochloride (ZH) and ractopamine hydrochloride (RAC) on feedlot performance, carcase characteristics of cattle and Warner Bratzler shear force (WBSF) of muscles. It was conducted to evaluate the effect of the use of these agents on beef production and meat quality and to provide data that would be useful in considerations on the effect of these agents on meat quality in Meat Standards Australia evaluations. We conducted a comprehensive literature search and study assessment using PubMed, Google Scholar, ScienceDirect, Scirus, and CAB and identification of other studies from reference lists in papers and searches. Searches were based on the key words: zilpaterol, zilmax, ractopamine, optaflexx, cattle and beef. Studies from theses obtained were included. Data were extracted from more than 50 comparisons for both agents and analysed using meta-analysis and meta-regression. Both agents markedly increased weight gain, hot carcase weight and longissimus muscle area and increased the efficiency of gain:feed. These effects were particularly large for ZH, however, fat thickness was decreased by ZH, but not RAC. Zilpaterol also markedly increased WBSF by 1.2 standard deviations and more than 0.8 kg, while RAC increased WBSF by 0.43 standard deviations and 0.2 kg. There is evidence in the ZH studies, in particular, of profound re-partitioning of nutrients from fat to protein depots. This work has provided critically needed information on the effects of ZH and RAC on production, efficiency and meat quality.

Effects of ovariectomization and ractopamine hydrochloride inclusion on heifer feedlot performance, meat yield, and tenderness of select muscles

Forty-eight British cross heifers were used to examine the effects of ovariectomization (OVX v. intact; INT) and ractopamine-HCl inclusion (0 or 0.41 mg/kg of BW day(-1); NORAC or RAC) for the final 31 days on performance, meat yield, and tenderness of select muscles. Ractopamine supplemented heifers had heavier BW (P≤0.05) and greater dressing percent than NORAC. Dressing percent was also greater (P<0.01) for INT v. OVX. LM area tended to be larger for RAC (P=0.07) and was larger for INT (P=0.05). Neither ractopamine inclusion nor sex class affected (P>0.08) organ weights or percent intramuscular fat. Ractopamine inclusion increased (P≤0.05) subprimal weight for the shoulder clod and bottom round. However, ractopamine inclusion and sex class had minimal effects on subprimal yields or slice shear force. Heifers receiving ractopamine had increased BW, DP, carcass weight and select subprimal weights without impacting meat quality. Ovariectomization did not influence the affects of ractopamine supplementation.

Reduced response to an estrous induction program in postpartum beef cows treated with zilpaterol and gaining body weight

In beef cows, reduced energy intake delays first ovulation postpartum and is associated with lesser insulin, IGF-I and leptin concentrations. However, the close relationship among these hormones mask their individual roles in the reinitiation of ovarian activity. A β-adrenergic receptor agonist (βAR) was used to increase body condition score (BCS) and yet reduce body fat and leptin serum concentration to determine the specific role of leptin in the postpartum ovarian activity. Beef cows (n=77) with BCS 3.1 ± 1.4 received 2 kg/day of feed containing 0 or 0.15 mg/kg of zilpaterol (a synthethic βAR), for 33 days. Estrus was induced with a progestin implant applied for 9 d and cows in estrus were bred by artificial insemination (AI). Zilpaterol administration increased (P<0.05) daily weight gain, muscle depth and BCS, with no changes in back fat depth, reducing fat to muscle ratio (P<0.05). At the time of AI, insulin (38%) and IGF-I (26%) concentrations were less in zilpaterol-treated cows (P<0.05), but leptin concentration was unaffected. Ovulation rate and animal with luteal activity after estrus induction were also reduced by 35% (P=0.05) and 56.5% (P=0.007), respectively, in zilpaterol-treated cows. Logistic regression estimates for BCS (P=0.016) and IGF-I concentration (P=0.03) were positively related with the occurrence of luteal activity. In addition, whilst back fat (P=0.009) had a positive effect on luteal activity, leptin concentration did not show a significant relationship. In conclusion, despite an increase in body weight and a positive change in BCS, the reduction in insulin and IGF-I concentrations, associated with βAR treatment, reduced the response to induction of estrus. However only IGF-I, but not leptin or insulin, significantly influenced the odds for the occurrence of luteal activity after estrous induction in cattle with poor BCS.

Effects of sequential feeding of β-adrenergic agonists on cull cow performance, carcass characteristics, and mRNA relative abundance

The objectives of this study were to determine the effects of supplementation with a single β-adrenergic agonist (β-AA) or a sequence of β-AA on cow performance, carcass characteristics, and mRNA relative abundance of cull cows implanted and fed a concentrate diet. Sixty cull cows were implanted with Revalor-200 (200 mg of trenbolone acetate and 20 mg of estradiol) and assigned to 1 of 4 treatments (n = 15/treatment): CON = fed a concentrate diet only; RH = supplemented with ractopamine-HCl for the last 25 d before slaughter; ZH = supplemented with zilpaterol-HCl for 20 d before a 3-d withdrawal before slaughter; RH + ZH = supplemented with RH for 25 d, followed by ZH for 20 d before a 3-d withdrawal before slaughter. Ractopamine-HCl was supplemented at a dose of 200 mg·animal(-1)·d(-1), and ZH was supplemented at 8.33 mg/kg (100% DM basis) of feed. All cows were fed a concentrate diet for 74 d. Each treatment had 5 cows per pen and 3 replicate pens. Body weights were collected on d 1, 24, 51, and 72. Muscle biopsies from the LM were collected on d 24, 51, and at slaughter from a subsample of 3 cows per pen. Carcass traits were evaluated postslaughter. The 2 ZH treatments averaged 15.3 kg more BW gain, 0.20 kg greater ADG, and 7.8 cm(2) larger LM area than CON and RH treatments, and 21 kg more HCW than CON, but these differences were not significant (P > 0.10), likely due to a sample size of n = 15/treatment. The sequence of RH followed by ZH tended to optimize the combination of HCW, LM area, percent intramuscular fat, and lean color and maturity compared with the ZH treatment. Abundance of β(2)-adrenergic receptor (AR) mRNA was not altered in the RH + ZH treatment during RH supplementation from d 24 to 51 of feeding. However, the abundance of β(2)-AR mRNA increased (P < 0.05) the last 23 d of feeding for the RH treatment and tended (P = 0.10) to increase in ZH cows during ZH supplementation. For all cows, abundance of type IIa myosin heavy chain (MHC-IIa) mRNA decreased (P < 0.05) after 24 d of feeding. Abundance of MHC-IIx mRNA increased (P < 0.05) for ZH and RH + ZH treatments the last 23 d of feeding during ZH supplementation. Although few significant differences were observed in performance or carcass traits, mRNA quantification indicated that β-AA supplementation elicited a cellular response in cull cows. Implanting and feeding cull cows for 74 d, regardless of β-AA supplementation, added economic value by transitioning cows from a cull cow to what is referred to in industry as a white cow market in which cows have white fat resulting from grain feeding.

Modification of muscle inherent properties through age at slaughter, growth promotants and breed crosses

Girard, I., Aalhus, J. L., Basarab, J. A., Larsen, I. L. and Bruce, H. L. 2011. Modification of muscle inherent properties through age at slaughter, growth promotants and breed crosses. Can. J. Anim. Sci. 91: 635–648. A 24 factorial experiment tested the interactions of slaughter age (12–13 or 18–20 mo), growth hormone use, β-adrenergic agonist (β-AA) use and breed cross [Hereford–Aberdeen Angus (HAA) or Charolais–Red Angus (CRA)] on the composition, fibre types, and connective tissue characteristics of m. semitendinosus (ST) and m. gluteus medius (GM) from 112 crossbred steers. Muscle weights increased with slaughter age, implantation and CRA genetics (P<0.05), but were not affected by ractopamine hydrochloride (RAC) (P>0.10).Animal age increased fast glycolytic (FG) and decreased fast oxidative glycolytic (FOG) fibre percentages by 7.2 and 6.6%, respectively, in the ST and increased slow oxidative (SO) and FOG fibre areas in both muscles (P<0.05). Cross-sectional areas of all fibre types were increased in the ST with implantation. In the GM, implantation increased SO (3.1%) and reduced FOG (3.2%) fibre percentages, while RAC reduced the SO (3.8%) and increased the FG (6.1%) fibre percentages (P<0.05).Only GM total collagen content increased with slaughter age (P<0.05),but collagen solubility decreased with slaughter age for both muscles (P<0.05). CRA genetics increased FG percentage in the GM of yearling-fed steers and increased moisture and protein and reduced fat contents of both muscles (P<0.05). In the muscles studied, IMP, slaughter age and animal genetics induced greater changes in muscle inherent properties than RAC.

Removal of supplemental vitamin A from barley-based diets improves marbling in feedlot heifers

Gibb, D. J., Van Herk, F. H., Mir, P. S., Loerch, S. and McAllister, T. A. 2011. Removal of supplemental vitamin A from barley-based diets improves marbling in feedlot heifers. Can. J. Anim. Sci. 91: 669–674. The objective of this research was to determine if removing supplemental vitamin A from barley-based feedlot diets affects animal performance, health, or carcass quality. Six pens per treatment (10 heifers per pen) were randomly assigned to receive zero (–VA) or 3640 (+VA) IU kg−1 dry matter of supplemental vitamin A in barley-based feedlot diets. Initial serum retinol was similar between treatments (28 µg dL−1; P=0.34), but –VA reduced levels by 40% (30 vs. 50 µg dL−1; P<0.001) by day 217. Removal of supplemental vitamin A reduced dry matter intake during the 58 d backgrounding period (6.93 vs. 7.07 kg d−1; P=0.007) and over the 218-d trial (9.18 vs. 9.35 kg d−1; P<0.001), but had no effect on average daily gain during backgrounding (1.22 kg d−1; P=0.46) or over all (1.46 kg d−1; P=0.15). Based on camera grading, –VA increased degree of marbling (480.6 vs. 439.3; P=0.02) without affecting backfat thickness (0.74 cm; P=0.62). Ultrasound measurements were highly correlated with camera grading, but did not detect treatment difference in marbling score (P=0.99). Results from this study show that the removal of supplemental vitamin A increased marbling without affecting backfat, gains, or animal health.

Zilpaterol hydrochloride alters abundance of β-adrenergic receptors in bovine muscle cells but has little effect on de novo fatty acid biosynthesis in bovine subcutaneous adipose tissue explants

We predicted that zilpaterol hydrochloride (ZH), a β-adrenergic receptor (AR) agonist, would depress mRNA and protein abundance of β-AR in bovine satellite cells. We also predicted that ZH would decrease total lipid synthesis in bovine adipose tissue. Bovine satellite cells isolated from the semimembranosus muscle were plated on tissue culture plates coated with reduced growth factor matrigel or collagen. Real-time quantitative PCR was used to measure specific gene expression after 48 h of ZH exposure in proliferating satellite cells and fused myoblasts. There was no effect of ZH dose on [(3)H]thymidine incorporation into DNA in proliferating myoblasts. Zilpaterol hydrochloride at 1 µM decreased (P < 0.05) β1-AR mRNA, and 0.01 and 1 µM ZH decreased (P < 0.05) β2-AR and β3-AR mRNA in myoblasts. The expression of IGF-I mRNA tended to increase (P = 0.07) with 1 µM ZH. There was no effect (P > 0.10) of ZH on the β-AR or IGF-I gene expression in fused myotube cultures at 192 h or on fusion percentage. The β2-AR antagonist ICI-118, 551 at 0.1 µM attenuated (P < 0.05) the effect of 0.1 µM ZH to reduce expression of β1- and β2-AR mRNA. The combination of 0.01 µM ZH and 0.1 µM ICI-118, 551 caused an increase (P < 0.05) in β1-AR gene expression. There was no effect (P > 0.10) of ICI-118, 551 or ZH on β3-AR or IGF-I. Western blot analysis revealed that the protein content of β2-AR in ZH-treated myotube cultures decreased (P < 0.05) relative to control. Total lipid synthesis from acetate was increased by ZH in bovine subcutaneous adipose tissue explants in the absence of theophylline but was decreased by ZH when theophylline was included in the incubation medium. These data indicate that ZH alters mRNA and protein concentrations of β-AR in satellite cell cultures, which in turn could affect responsiveness of cells to prolonged ZH exposure in vivo. Similar to other β-adrenergic agonists, ZH had only modest effects on lipid metabolism in adipose tissue explants.

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.

Manipulating grain processing method and roughage level to improve feed efficiency in feedlot cattle

The effects of feeding finishing diets containing whole corn with no roughage on performance and carcass characteristics of feedlot steers were evaluated in 6 trials conducted at commercial research facilities (Bos Technica Research Services Inc., Salina, KS) in the Southern Plains of the United States. One hundred and two feedlot pens containing 6,895 steers were represented. All trials were designed as randomized complete blocks with pen serving as the experimental unit. Steers were fed and managed similarly across all trials. Treatments consisted of a typical control finishing diet with various grain sources and processing methods that contained roughage and a finishing diet containing whole corn (8 to 23% of diet DM) but without added roughage. Final BW was greater (P < 0.1) for steers fed typical finishing diets than for steers fed whole corn diets without roughage in 5 of the 6 trials. Feeding finishing diets containing whole corn but without roughage resulted in decreased (P < 0.1) ADG and carcass ADG in 5 of the 6 trials. However, DMI also was less (P < 0.1) for steers fed whole corn finishing diets without roughage in all trials such that feeding whole corn diets without roughage improved (P < 0.05) G:F (BW basis) in 2 of the 6 trials, and improved (P < 0.1) G:F based on carcass weight in 5 of the 6 trials. Dry matter intake as a percentage of BW daily across trials was well predicted from percentage of dietary NDF from roughage, being 1.906 + 0.0199 (+/-0.0012) NDF (P < 0.05). Performance-based NE(g) content of the diet was greater (P < 0.07) for steers fed whole corn diets without roughage. Differences in USDA yield and quality grades were inconsistent. Results indicate that feeding diets containing whole corn with no added roughage tends to decrease DMI and ADG in finishing steers, but improves feed efficiency and performance-calculated dietary NE(g).

Effect of ractopamine-hydrochloride on the fiber type distribution and shelf-life of six muscles of steers

The goal of this study was to evaluate the effects of ractopamine-hydrochloride (RAC) supplementation on the myosin heavy chain isoform distribution and shelf-life properties of muscles from beef top round, knuckle, and loin. Thirty-four steer carcasses were selected from 4 separate slaughter groups. Within each slaughter group (3 groups, n = 8; 1 group, n = 10), steers were separated into pens (n = 8) and fed 0 or 200 mg x animal(-1) x d(-1) of RAC for the final 28 d of feeding. Seventy-two hours postmortem, the longissimus lumborum, semimembranosus (SM), adductor, gracilis, vastus lateralis (VL), and rectus femoris were removed from each carcass. A subsample of each muscle was collected for immunohistochemical analysis. Whole muscles were vacuum packaged and wet aged at 1 +/- 2 degrees C for 13 d before processing into steaks for a 5-d simulated retail display study. Daily, steaks were analyzed for reduction of nitric oxide metmyoglobin, lean color, fat color, and surface discoloration. Objective measures of metmyoglobin, oxymyoglobin, L*, a*, and b* values were recorded daily. Ractopamine significantly (P < 0.05) changed the fiber type isoform distribution in all muscles except the SM. The VL and gracilis presented the greatest fiber type switch with approximately 21% of type I fibers switching to type IIA fibers. However, the fiber type shifts induced by RAC supplementation had little to no effect on subjective and objective color measurements during the 5-d retail display period. Metmyoglobin and oxymyoglobin accumulation, L*, a*, and b*-values were not affected (P > 0.05) by RAC supplementation. Percent nitric oxide metmyoglobin reduction data indicate that reducing ability of RAC-treated steaks from the adductor and longissimus lumborum were significantly affected (P < 0.05). Visual panel data suggest that RAC tended (P < 0.10) to have the most detrimental effect on the lean color and surface discoloration scores of steaks from the VL during the last 3 d of display. Ractopamine significantly (P < 0.05) increased the surface discoloration of the rectus femoris and SM on d 5. Although RAC supplementation had no effect on objective color measurements, subjective measurements indicate that it may have some effect on surface discoloration of some muscles.