Veterinary Clinics of North America-Food Animal Practice最新文献

The primary goals of cattle production are to enhance economic gains and operational margins through sound nutrition, health, stewardship, and business management. Anabolic growth implants improve beef production efficiency by reducing resource inputs such as feed, water, and land, thus lowering environmental impact. These implants contain hormones like estrogens, androgens, or progestins, which are naturally produced in mammals. Administered via subcutaneous implants in the ear, they release hormones gradually into the bloodstream, promoting growth. Supported by FDA approval since the 1950s, these implants have helped the U.S. cattle industry produce safe, high-quality, abundant beef efficiently for global consumption.

Across decades of research, implants consistently improve growth: suckling calves gain roughly 6% to 15% more ADG and wean about 10.4 kg heavier, while backgrounded cattle commonly realize 14% to 16% greater ADG. Administering a single calfhood implant to a replacement heifer within the recommended 1 to 4 month window does not depress fertility; problems arise chiefly with very early, late, or multiple implants. Marketing calves into an all-natural or non-hormone treated cattle program are the main reason to forgo implants; however, market data show no price penalty at auction for implanted lots.

Feedlot implants consistently increase growth, improve feed efficiency, and add carcass weight when aligned with genetics, dietary energy, and marketing endpoints. Across studies summarized in this article, average responses to implants are 10% to 30% greater average daily gain and 5% to 15% improved G:F, with the greatest biological response early in the payout period. Steers generally respond greater to implants than heifers; heifer responses are directionally similar but smaller. Coated (extended-release) implants lengthen payout and may reduce reimplant labor, whereas reimplant programs can capture higher peaks in gain but sometimes transiently depress dry matter intake.

Understanding growth physiology in cattle is essential for optimizing beef production efficiency and carcass quality. This review explores the biological mechanisms underlying muscle, fat, and bone development from prenatal to postnatal stages, emphasizing the roles of cell differentiation, hormonal regulation, and nutritional inputs. Growth is allometric, with tissue-specific rates of accretion that shift as cattle mature. Hormones such as estrogen, testosterone, and insulin-like growth factor 1 influence tissue development, whereas genetic selection and breed differences affect tissue growth rates and carcass traits. This review provides a comprehensive framework for applying growth physiology principles to modern fed cattle management.

Steroidal implants are widely used in feedlot cattle to improve growth and feed efficiency. This article emphasizes best practices for their proper handling, storage, and application to ensure effectiveness. Key points include maintaining optimal storage conditions, correct placement in the middle third of the ear, using clean equipment, and trained personnel to prevent complications like abscesses, missed implants, or abnormalities that can reduce performance response. Routine checks are recommended to identify issues early. Proper sanitation, staff training, and monitoring of implant retention are essential for maximizing cattle growth, health, and profitability. Adhering to these practices ensures optimal results.

Beta-adrenergic agonists (β-AA) enhance beef production efficiency, carcass leanness, and emissions intensity, offering consistent economic returns for cattle feeders and beef packers. Numerous research experiments have been published to quantify the effects of ractopamine hydrochloride, zilpaterol hydrochloride, and lubabegron fumarate on live gain and carcass characteristics. β-AA response remains additive with other growth-enhancing technologies and incrementally improves growth performance, carcass merit, sustainability, and profitability late in the feeding period (last 14-91 days).

Growth enhancing technologies (GETs) are routinely used in finishing beef cattle production to enhance growth, feed efficiency, and sustainability. However, concerns surround the use of GETs and their impact on marbling score and eating quality. The use of GETs can impact marbling deposition, percentage of cattle grading USDA Choice, tenderness, and consumer acceptability; however, the results are variable depending on the anabolic implant type, beta-adrenergic agonist type, and combinations used during the finishing period. This review will summarize how GETs impact meat quality and offer strategies that may help to minimize their impact on marbling and tenderness.

Beta-adrenergic agonists (β-AAs) are synthetic compounds structurally related to catecholamines that activate β-adrenergic receptors (β-ARs), thereby stimulating intracellular signaling cascades, most notably the cAMP-PKA pathway. In livestock, β-AAs promote nutrient partitioning by shifting energy utilization from fat deposition to lean tissue accretion. Ractopamine and zilpaterol, which primarily act on β₁-and β₂-receptors, respectively, have been widely adopted in North American beef production to enhance growth efficiency. More recently, lubabegron (Experior), a β₃-selective agonist approved in 2018, has gained attention for its dual role in improving feedlot performance and reducing ammonia emissions.

Beta-adrenergic agonists and selective β-adrenergic modulators are unique growth promoting technologies that elicit responses independent of growth implants. These compounds work through specific receptors located throughout the body to increase protein accretion through signaling events leading to metabolic modulation. The β-adrenergic recetors differ in their physiologic location and active life. Prolonged exposure of β₁ and β₂ receptors to ligands causes desensitization and receptor internalization, whereas β₃ receptors differ in structure and have an extended half-life. Three β-adrenergic agonists and selective β-adrenergic modulators have been approved for use in cattle feeding in the United States.

Implant effects on growth are typically well understood, while behavioral (ie, riding) carcass-quality (ie, marbling or reduction in dairy-type muscling) are more variable. A newer challenge related to implant use is recent Food and Drug Administration guidance placing greater restrictions on allowable reimplanting protocols. If approved for a reimplant program, a maximum of 2 implants can be used during finishing. This article will discuss the use of this technology with special emphasis placed on items that should be considered when developing an effective implant strategy for all classes of cattle across all production phases.