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Decreasing nitrogen for volatilization in beef feedlot cattle




Kappen, Maria M., author
Archibeque, Shawn L., advisor
Engle, Terry E., committee member
Ham, Jay M., committee member

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The effects of ractopamine hydrochloride (RAC) and a steroidal implant (IMP), on whole body N metabolism were evaluated in 24 Hereford x Angus steers (BW 554.4 ± 26.8 kg). The experimental design was a completely randomized block design with a 2 x 2 factorial arrangement of treatments. Factors included: 1) RAC (0.0 or 400 mg×steer-1×d-1) and 2) IMP (0.0 or 200 mg trenbolone acetate and 28 mg of estradiol benzoate). Steers were housed in individual pens and allowed ad libitum access to feed and water throughout the experiment. Steers were acclimated to the metabolism barn by bringing in, tying and currying for 12 d before the initiation of the experiment. Once cattle had been implanted for 48 d and had received RAC for 21 d, a nutrient balance study was conducted for 6 d. An IMP x RAC interaction tended (P < 0.09) to exist for DMI. Implanted steers receiving RAC tended to have lower DMI compared to non-IMP steers receiving RAC as well as IMP steers not receiving RAC. N intake (P > 0.11) and fecal N (P > 0.18) were not different due to treatment, yet numerically reflected the trend noted for DMI. Urinary N excretion was decreased by feeding RAC (P < 0.01). There tended (P < 0.08) to be an IMP x RAC interaction for urinary N excretion. Implanted steers receiving RAC tended to have less urinary N than steers receiving an implant only. Similarly, urine urea N excretion was decreased by RAC treatment (P < 0.02) and excretion tended to be decreased in steers that had also received IMP (IMP x RAC interaction; P < 0.07). Overall N retention was not affected by treatment (P > 0.14). These results indicate that urinary N excretion can be reduced by incorporating RAC according to labeled usage during the final phase of the finishing period. However, more studies will be required to elucidate the potential interactions of RAC with implant status and types of implants.


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ractopamine hydrochloride
estradiol benzoate
nitrogen balance
trenbolone acetate
urinary nitrogen
urinary urea nitrogen


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