Masters Theses

Date of Award

12-1979

Degree Type

Thesis

Degree Name

Master of Science

Major

Animal Science

Major Professor

J. W. Holloway

Committee Members

K. M. Barth, W. T. Butts Jr.

Abstract

Six in vivo digestion trials were conducted, in which a total of thirty-nine fecal samples were obtained from Angus steers receiving tall fescue-legume mixtures of varying proportions. The forages were of diverse maturities and digestibilities. The forage and fecal samples were analyzed for dry matter, nitrogen, ether extract, crude fiber, ash, cell wall constituents, acid-detergent fiber, acid-detergent lignin, in vitro dry matter digestibility, and in vitro organic matter digestibility, and in addition, the fecal samples were analyzed for acid-insoluble ash, sodium, zinc, and urobilinogen. Nitrogen-free extract, cellulose, hemicellulose, and acid-soluble ash were calculated. Wet matter intake, dry matter intake, wet fecal output, fecal dry matter output, dry matter digestibility, digestible dry matter intake, total digestible nutrients, total digestible nutrient intake, crude protein digestion coefficient, and digestible crude protein intake were determined for each steer. A factor analysis was conducted to aid in explaining how each variable was related to other variables. Several equations were developed in which fecal variables served as indpendent variables for the prediction of digestion trial variables. For each dependent variable, a series of multiple regression equations containing one to eleven variables was formulated which best predicted (maximum R²) that particular variable. These equations included squared and interaction terms of fecal variables when its addition produced greater increase in R² values than addition of any other variable. Over 91% and 89% of the variation in wet matter intake and dry matter intake, respectively, were accounted for with each best-fit eleven-variable index. The fecal index containing ten independent variables explained almost 65% of the variation in wet fecal output, whereas the eleven-variable model for prediction of fecal dry matter output explained about 63% of its variation. A ten-variable model provided a fecal index which explained approximately 79% of the variation in dry matter digestibility; 81.62% of the variation in digestible dry matter intake was accounted for by the best-fit eleven-variable prediction equation. The eleven-variable indices developed for the prediction of total digestible nutrients and total digestible nutrient intake explained approximately 88% and 85% of the variation, respectively. Digestible crude protein and digestible crude protein intake, when predicted from eleven-variable models, accounted for over 88% of the variation in each of these dependent variables. The R² values obtained from these fecal indices support the theory that the fecal index technique is a valuable method of evaluation of pasture, and that large amounts of variation can be accounted by using a broad spectrum of forage compositions.

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