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

The Crossroads between Zinc and Steroidal Implant-Induced Growth of Beef Cattle

Growth-promoting technologies such as steroidal implants have been utilized in the beef industry for over 60 years and remain an indispensable tool for improving economic returns through consistently improved average daily gain via increased skeletal muscle hypertrophy. Zinc has been implicated in skeletal muscle growth through protein synthesis, satellite cell function, and many other growth processes. Therefore, the objective of this review was to present the available literature linking Zn to steroidal implant-induced protein synthesis and other metabolic processes. Herein, steroidal implants and their mode of action, the biological importance of Zn, and several connections between steroidal implants and Zn related to growth processes are discussed. These include the influence of Zn on hormone receptor signaling, circulating insulin-like growth factor-1 concentrations, glucose metabolism, protein synthesis via mTOR, and satellite cell proliferation and differentiation. Supplemental Zn has also been implicated in improved growth rates of cattle utilizing growth-promoting technologies, and steroidal implants appear to alter liver and circulating Zn concentrations. Therefore, this review provides evidence of the role of Zn in steroidal implant-induced growth yet reveals gaps in the current knowledge base related to optimizing Zn supplementation strategies to best capture growth performance improvements offered through steroidal implants.

Level and source of fat in the diet of gestating beef cows: II. Effects on the postpartum performance of the dam and the progeny

A study was conducted to evaluate the effects of level and source of fat in the diet of gestating beef cows on the postpartum performance of the dam and the progeny. Each year, 75 mature pregnant (183±4.8 d until calving) Angus cows with similar BW (663±21.5 kg) and BCS (2.6±0.12; 1 to 5 scale) were randomly assigned to one of 15 outdoor pens. Each pen was assigned to one of three iso-caloric and iso-nitrogenous treatments: a low-fat diet (LF; 1.4±0.12% EE), and two high-fat diets (HF; 3.3±0.20% EE) including a canola seed (CAN) or a flaxseed (FLX) based pelleted feed. Diets were formulated to meet the requirements of pregnant beef cows and fed until calving. Data were analyzed as a randomized complete block design with contrasts for the effects of level (LF vs. HF) and source (CAN vs. FLX) of fat. No differences (P≥0.21) were found for BW or calving to weaning ADG of cows. The average BCS during the first 42 d of lactation was greater (P<0.01) for LF compared to HF (2.63 vs. 2.51) with no difference (P=0.35) for CAN vs. FLX cows. Subcutaneous fat thickness over the ribs was greater (P≤0.01) for LF compared to that of HF cows at calving (5.7 vs. 4.3 mm) and at weaning (4.3 vs. 3.7 mm) with no difference (P≥0.11) for CAN vs. FLX cows. Over the first 42 d of lactation, no difference (P≥0.23) was observed for 12-h milk yield. Milk protein concentration was greater (P=0.03) for CAN compared to FLX (3.11 vs. 3.01%) cows while no difference (P≥0.28) was observed for any other milk component. Milk fat from FLX cows had greater (P < 0.01) CLA and CLnA concentrations than that of CAN cows during the first 42 d of lactation. Pregnancy rate of HF cows tended (P=0.07) to be greater than that of LF cows with no difference (P=0.77) for CAN vs. FLX cows. Calves from HF cows were heavier (P≤0.01) at birth (42.9 vs. 40.2 kg) than those from LF cows. From calving to weaning, ADG of calves born to CAN cows was greater (P=0.03) that that of calves born to FLX cows (1.19 vs. 1.13 kg/d) with no difference (P=0.18) for calves born to LF vs. HF cows. At slaughter, progeny of HF cows had greater (P≤0.03) shrunk BW (605 vs. 579 kg) and HCW (355 vs. 339 kg) compared to those from LF cows with no difference (P≥0.16) for progeny of CAN vs. FLX cows. These results show that feeding a HF diet over gestation results in heavier calves at birth and at slaughter, and superior calf gains from birth to slaughter as well as heavier carcasses, possibly due to a developmental programming effect.

Effects of steroid treatment on growth, nutrient partitioning, and expression of genes related to growth and nutrient metabolism in adult triploid rainbow trout (Oncorhynchus mykiss)

The contribution of sex steroids to nutrient partitioning and energy balance during gonad development was studied in rainbow trout. Specifically, 19-mo old triploid (3N) female rainbow trout were fed treatment diets supplemented with estradiol-17β (E2), testosterone (T), or dihydrotestosterone at 30-mg steroid/kg diet for a 1-mo period. Growth performance, nutrient partitioning, and expression of genes central to growth and nutrient metabolism were compared with 3N and age-matched diploid (2N) female fish consuming a control diet not supplemented with steroids. Only 2 N fish exhibited active gonad development, with gonad weights increasing from 3.7% to 5.5% of body weight throughout the study, whereas gonad weights in 3N fish remained at 0.03%. Triploid fish consuming dihydrotestosterone exhibited faster specific growth rates than 3N-controls (P < 0.05). Consumption of E2 in 3N fish reduced fillet growth and caused lower fillet yield compared with all other treatment groups (P < 0.05). In contrast, viscera fat gain was not affected by steroid consumption (P > 0.05). Gene transcripts associated with physiological pathways were identified in maturing 2N and E2-treated 3N fish that differed in abundance from 3N-control fish (P < 0.05). In liver these mechanisms included the growth hormone/insulin-like growth factor (IGF) axis (igf1, igf2), IGF binding proteins (igfbp1b1, igfbp2b1, igfbp5b1, igfbp6b1), and genes associated with lipid binding and transport (fabp3, fabp4, lpl, cd36), fatty acid oxidation (cpt1a), and the pparg transcription factor. In muscle, these mechanisms included reductions in myogenic gene expression (fst, myog) and the proteolysis-related gene, cathepsin-L, suggesting an E2-induced reduction in the capacity for muscle growth. These findings suggest that increased E2 signaling in the sexually maturing female rainbow trout alters physiological pathways in liver, particularly those related to IGF signaling and lipid metabolism, to partition nutrients away from muscle growth toward support of maturation-related processes. In contrast, the mobilization of viscera lipid stores appear to be mediated less by E2 and more by energy demands associated with gonad development. These findings improve the understanding of how steroids regulate nutrient metabolism to meet the high energy demands associated with gonad development during sexual maturation.

Improvements in body composition, cardiometabolic risk factors and insulin sensitivity with trenbolone in normogonadic rats

Trenbolone (TREN) is used for anabolic growth-promotion in over 20 million cattle annually and continues to be misused for aesthetic purposes in humans. The current study investigated TREN's effects on body composition and cardiometabolic risk factors; and its tissue-selective effects on the cardiovascular system, liver and prostate. Male rats (n=12) were implanted with osmotic infusion pumps delivering either cyclodextrin vehicle (CTRL) or 2mg/kg/day TREN for 6 weeks. Dual-energy X-ray Absorptiometry assessment of body composition; organ wet weights and serum lipid profiles; and insulin sensitivity were assessed. Cardiac ultrasound examinations were performed before in vivo studies assessed myocardial susceptibility to ischemia-reperfusion (I/R) injury. Circulating sex hormones and liver enzyme activities; and prostate and liver histology were examined. In 6 weeks, fat mass increased by 34±7% in CTRLs (p<0.01). Fat mass decreased by 37±6% and lean mass increased by 11±4% with TREN (p<0.05). Serum triglycerides, HDL and LDL were reduced by 62%, 57% and 78% (p<0.05) respectively in TREN rats. Histological examination of the prostates from TREN-treated rats indicated benign hyperplasia associated with an increased prostate mass (149% compared to CTRLs, p<0.01). No evidence of adverse cardiac or hepatic effects was observed. In conclusion, improvements in body composition, lipid profile and insulin sensitivity (key risk factors for cardiometabolic disease) were achieved with six-week TREN treatment without evidence of adverse cardiovascular or hepatic effects that are commonly associated with traditional anabolic steroid misuse. Sex hormone suppression and benign prostate hyperplasia were confirmed as adverse effects of the 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.

Subcutaneous fatty acid composition of steers finished as weanlings or yearlings with and without growth promotants

BACKGROUND

The current study evaluated the subcutaneous fatty acid (FA) composition of calf- and yearling-fed steers with or without growth promoting implants. Crossbred steers (n = 112; 267 ± 5.0 kg) of the same contemporary group were allocated to one of four production system and implant strategy based treatments in a completely randomized design with a 2 × 2 factorial arrangement of treatments.

RESULTS

There were no interactions (P > 0.05) between production systems and growth promoting implants for the total and individual subcutaneous FA. Yearling as opposed to calf finishing reduced (P < 0.05) subcutaneous proportions of C20:3n-6, trans (t)12-18:1, C14:0, several minor cis-monounsaturated FA (c-MUFA; c9-14:1, c11-16:1, c11-18:1, c12-18:1, c13-18:1, c9-20:1 and c11-20:1), and increased (P < 0 .05) subcutaneous proportions of t11c15-18:2, total and individual branched-chain FA. Subcutaneous fat from steers implanted with growth promotants had higher (P < 0.05) proportions of total polyunsaturated FA (PUFA), total n-6 PUFA, C18:2n-6 and individual t-18:1 isomers (t6 to t10) compared to non-implanted steers.

CONCLUSIONS

Overall, current findings show that production systems and growth promotants led to only minor differences in subcutaneous FA composition of beef steers.

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.