Date of Graduation

8-2019

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Animal Science (PhD)

Degree Level

Graduate

Department

Animal Science

Advisor/Mentor

Beck, Paul A.

Committee Member

Apple, Jason K.

Second Committee Member

Zhao, Jiangchao

Third Committee Member

Kelley, Jason P.

Keywords

cattle; feed additives; feed efficiency; ionophore; monensin; weight gain

Abstract

Three monensin levels during a stocker phase (0, 800, 1600 g/ton in a free choice mineral) and two levels during finishing (0 [U] or 37.5 mg/kg diet DM [M]) were used to determine the effects of monensin supplementation during a stocker and subsequent finishing phase on beef calves. Steers (n = 605, BW = 278 ± 27 kg) were fed pearl millet hay with soybean hull and corn gluten feed supplement (0.5% BW daily [AF basis] Block 1) or grazed fall wheat (Block 2), spring wheat (Block 3), bermudagrass (Blocks 4 & 5) or wheat with mixed-grass baleage (Block 6). A subset of calves were transported 1,068 km to Canyon, TX (blocks 1, 2, and 4) or 636 km to Stillwater, OK (block 6) for finishing. Rumen fluid was collected on a subset of cattle (n = 30) throughout the experiment to characterize rumen microbiota by next generation sequencing. There were no treatment × diet interactions (P ≥ 0.96) during the stocker phase or location × treatment interactions (P ≥ 0.19) during finishing, therefore data were pooled for statistical analysis. During the stocker phase, cattle consuming monensin had greater (P = 0.01) final BW compared with the 0 treatment. Steers on 800 and 1600 had greater ADG (P = 0.02) and total gain (P = 0.02) than 0. Mineral intake decreased (P < 0.01) as monensin level increased. Stocker × feedlot treatment interactions were not observed for feedlot performance (P ≥ 0.50). Feedlot cattle consuming monensin had decreased (P < 0.01) DMI and increased (P < 0.01) G:F than those that did not. Cattle consuming monensin during finishing had increased (P = 0.03) fat thickness. During the stocker phase, monensin treatments had decreased alpha community (P ≤ 0.04) compared to the 0 treatment. Cattle previously on the 0 and 1600 treatments during the stocker phase and were fed monensin at the feedlot had decreased alpha diversity (P = 0.04) on feedlot d 14 compared to those that did not.

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