Date of Graduation

8-2012

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Animal Science (PhD)

Degree Level

Graduate

Department

Animal Science

Advisor

Kenneth P. Coffey

Committee Member

Dirk Philipp

Second Committee Member

Elizabeth B. Kegley

Third Committee Member

Charles P. West

Fourth Committee Member

Shane Gadberry

Fifth Committee Member

John Jennings

Keywords

Biological sciences; Beef cattle; Bermudagrass; Digestibility; Fecal sampling time; Internal marker

Abstract

The potential of in situ rumen undegradable dry matter (RUDM), indigestible neutral-detergent fiber (INDF), indigestible acid-detergent fiber (IADF), acid-detergent insoluble ash (ADIA), alkaline-peroxide lignin (APL), and acid-detergent lignin (ADL) to predict digestibility (DMD) and fecal output (FO) by cattle fed bermudagrass [Cynodon dactylon (L.) Pers.] hay-diets categorized by their low (L), medium low (ML), medium high (MH), or high (H) CP concentrations (79, 111, 131, and 164 g/kg DM, respectively) was evaluated. The second objective was to evaluate the effects of time (0600, 1200, 1800, and 2400 h) of fecal sampling on the prediction of FO and DMD. A replicated 4 × 4 Latin-Square with one period missing was employed where diets were offered in three 15-d periods to provide 2 replicates per diet per period (n = 24). Actual DMI, FO, and DMD were determined based on hay offered, orts, and feces excreted. Hay, orts, and feces were analyzed for RUDM, INDF, IADF, ADL, APL, and ADIA concentrations. Fecal recoveries of internal markers were expressed as the ratio of the quantity of marker excreted per unit of marker consumed. Estimate of FO and DMD were calculated by the marker ratio technique.

All in situ markers and ADL recoveries differed from 1. Estimates of DMD were underestimated while FO estimates were overestimated for all in situ markers. Recovery of APL tended to differ from 1, but ADIA recovery was not different from 1. Estimates of FO and DMD derived using APL and ADIA were not different from TC. Time of sampling affected the concentration of IADFa while ADIA and APL concentrations in fecal samples were not different. Estimates of FO and DMD by all fecal sampling times and their different combinations were not different from actual FO and DMD. Therefore APL and ADIA have the potential to predict FO and DMD of bermudagrass of various qualities fed to cattle and fecal sampling time may not be an issue when using internal markers.

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