Degree Type

Dissertation

Date of Award

1984

Degree Name

Doctor of Philosophy

Department

Animal Science

Abstract

The theory has been promoted that diet may influence compositional growth of cattle independently of genetic selection for body composition. Corn grain has been the preferred feedstuff for growing and finishing cattle in feedlots. Two trials (1 and 2) were conducted to profile and evaluate compositional growth in steers fed diets differing in energy (ME) and metabolizable protein (MP). Metabolizable energy (starch) and MP (corn gluten meal) derived from corn processing were used in six (trial 1) and four (trial 2) diets. Levels of ME ranged from 2.2 to 2.8 Mcal/kg of dry matter and MP levels ranged from 49.7 to 63.0 g/kg of dry matter. Four weanling Angus x Charolais steers per diet were individually fed, and measurements of average daily gain (ADG), feed efficiency (F/G), dry matter digestibility (DMD), protein digestibility (PDIG), efficiency of utilization of digestible protein and energy and empty body composition, as determined by deuterium oxide dilution, were obtained at approximately every 90 kg of live weight gain. In trial 2, serial blood samples were taken every 60 days to assay for growth hormone (GH), insulin (I), glucagon (G) and thyroid hormones (T3 and T4);Average daily gain was improved by addition of either nutrient, and had an additive effect when both ME and MP were added at the high level. As nutrient density increased, F/G improved. Only when both ME and MP levels were increased did DMD improve. In trial 1, PDIG improved at the high MP level, but was similar for all diet groups in trial 2. Steers receiving the higher ME levels were significantly fatter, and those receiving the higher MP levels at the low ME level were leanest. Efficiency of depositing dietary energy in body tissue increased with time on feed. The diets with the highest ME deviated from this trend and decreased in caloric efficiency in the final period. Efficiency of protein utilization showed an overall decrease with time, and no differences were observed between diets. Concentrations of growth hormone were elevated in steers fed the low MP:low ME diet. Plasma insulin/glucagon ratios were similar for all diet groups and periods measured. Concentrations of triiodothyronine were greater in steers on the high energy diets, whereas thyroxine concentrations tended to be lower.

DOI

https://doi.org/10.31274/rtd-180813-6837

Publisher

Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/

Copyright Owner

Eric James Hentges

Language

en

Proquest ID

AAI8505828

File Format

application/pdf

File Size

165 pages

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