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    Effects of growth implants on animal performance, intake, carcass characteristics, feeding behavior, enteric methane emissions, and economic profitability of finishing Angus steers
    (Colorado State University. Libraries, 2025) Swenson, Maya, author; Place, Sara, advisor; Stackhouse-Lawson, Kim, committee member; Engle, Terry, committee member; DeLay, Nathan, committee member
    Methane (CH4) is a potent greenhouse gas (GHG) with a global warming potential 28-34 times greater than carbon dioxide (CO2), making it a significant contributor to climate change (IPCC, 2019). Livestock production, particularly feedlot systems, is a major source of CH4 emissions from cattle, influenced by diet composition, microbial fermentation, and animal-specific traits (FAO, 2013; Beauchemin et al., 2020). Advances in CH4 measurement techniques including respiration chambers, SF 6 tracer methods, and automated head chamber systems (AHCS), have improved emissions quantification in feedlot settings (Harper et al., 1999; McGinn et al., 2019; Ungerfeld et al., 2022). Mitigations strategies include dietary interventions like high-concentrate diets, which promote propionate production over methanogenesis, and feed additives like 3-nitrooxypropanol (3-NOP), ionophores, seaweed, and nitrates, which can reduce CH4 emissions by 10-80% (Vyas et al., 2018; Almeida et al., 2021; Kebreab et al., 2023; Ungerfeld & Pitta, 2024). Additionally, manure management practices, such as anaerobic digesters and composting, can further reduce CH4 emissions from the livestock operations (EPA, 2024). Anabolic growth promoting implants, widely used in the beef industry, enhance G:F and ADG, have the potential to indirectly reduce CH4 emissions per unit of beef produced by 12-20% (Stackhouse et al., 2013; Reichhardt et al., 2021). Implants containing trenbolone acetate (TBA) and estradiol (E2) have been shown to increase average daily gain (ADG) by up to 28% and improve feed efficiency (G:F), reducing overall emissions intensity (Parr et al., 2011; Smith & Johnson, 2020). Therefore, the study's objective was to assess the relationship between animal performance, feed intake, carcass characteristics, feeding behavior, enteric CH4 emissions, and economic profitability of implanted and nonimplanted finishing Angus steers. Sixty-two cattle were housed at the Climate Smart Research pens at Colorado State University and blocked by body weight into two pens. Each pen was equipped with GreenFeed automated head chambers and SmartFeed feeder for feed intake and behavior measurement (C-Lock, Rapid City, SD). The study was conducted as a randomized complete block design. Animals within each pen were randomly assigned a treatment: implanted with Component TE200 (IMP) (Elanco Animal Health, Greenfield, IN) or not implanted (CON). Body weight (BW) gain, feed intake, and enteric emissions were collected from each individual animal for 80 and 52 d. Data were analyzed in JMP Pro and significance was declared at P < 0.05 with tendencies at P < 0.1. IMP animals had a greater final BW (709 kg vs 670 kg) and ADG (2.4 kg/d vs 1.7 kg/d, P < 0.0001) compared to CON animals. A greater dry matter intake (DMI) was observed in IMP animals (11.3 kg/d) compared to CON animals (10.9 kg/d, P = 0.01). IMP animals had improved feed conversion (F:G) and G:F efficiencies when compared with CON animals (P < 0.0001). A difference was observed in hot carcass weight (HCW) between IMP and CON animals (414.8 kg vs 386.5 kg, P < 0.0001). Similarly, ribeye area (REA) was larger in IMP animals compared to CON animals (P = 0.01). No differences were observed in marbling score and USDA yield grade (YG) between the two treatments (P > 0.05). There was a difference in USDA quality grade (QG), where CON animals graded more frequently in higher grade categories (Choice, Choice+, and Prime) compared to IMP animals (P = 0.04). IMP animals tended to have larger session size (SS) (g DM/visit) than CON animals (P = 0.08). An interaction was observed where IMP animals fed for 80 d had greater enteric CH4 emissions compared to CON animals within the same pen (199 g CH4/d vs 177 g CH4/d, P = 0.04). IMP animals had greater oxygen (O2) consumption and hydrogen (H2) emission than CON animals (P < 0.05). With animals fed for 52 d, IMP animals had reduced CH4 emissions intensity (g CH4/kg ADG) compared to CON animals (P < 0.05). Relative profitability was greater than $0 in both weight groups with mean differences of $111.76 and $143.39 for 52 and 80 DOF, respectively. In summary, anabolic implants improve feedlot animal productivity and efficiency, potentially reducing emissions per unit of beef produced while improving economic profitability.