Doctoral Dissertations

Date of Award

6-1976

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Animal Science

Major Professor

H. V. Shirley

Committee Members

J. B. McLaren, R. S. Dotson, Robert R. Shrode

Abstract

Data used in this study were collected during the Seventeenth and Eighteenth Tennessee Random Sample Laying Tests (1974 and 1975). Because of their importance to poultrymen many economic egg production traits were studied. Analysis of variance was conducted to determine the existence of the differences among stocks and treatments and of interactions. Stocks were found to differ significantly from each other with respect to most of the traits studied. To illustrate the differences among stocks, a ranking of their means with respect to each traits was prepared. Treatment effects (varying dietary salt levels and addition of bicarbonate and of methionine and choline) were found to be significant with respect to some tratis studied but not with respect to the others. A low level of salt (0.25%) was found to increase significantly (P < 0.05) average egg weight, and the same effect for low level of choline (i.e.. no added choline) was found. The low salt level had a significant (P < 0.001) influence in increasing percent small blood spots. Supplementary bicarbon-ate of soda significantly (P < 0.05) decreased percent mortality. Choline addition significantly (P < 0.05) increased the percentage of medium eggs. Addition of methionine to the layer diet significantly (P < 0.05) improved feed efficiency traits, i.e.. it significantly (P < 0.05) decreased amount of feed per bird housed, pounds of feed per pound of eggs and pounds of feed per dozen eggs. Supplementary methionine significantly (P < 0.001) decreased specific gravity. There were many indications of interaction. First-order inter-actions, salt-by-bicarbonate-levels interaction was significant (P < 0,05 and P < 0.01) with respect to average egg weight and percent peewee eggs. Stock-by-salt-level interaction was highly significant (P < 0.01) with respect to average egg weight and also significant (P < 0.05) with respect to final body weight, percent large eggs and Haugh units. Interaction of stock with bicarbonate was significant (P < 0.05) with respect to percent large eggs. Stock-by-choline interaction was significant (P < 0.05) with respect to percent large eggs and percent small meat spots. Stockby- methionine interaction was significant (P < 0.01) with respect to per cent large eggs and percent large meat spots. Interaction between choline and methionine was significant (P < 0.01) with respect to specific gravity. Second-order interaction of stock-by-salt-by-bicarbonate was significant (P < 0.05 and P < 0.01) with respect to average egg weight and percent large meat spots, respectively. Stock-by-choline-by-methionine interaction was significant (P < 0.05) with respect to percent small eggs, large eggs and extra-large eggs. The second kind of examination of the data was conducting Bartlett's Test of homogenity of variances. The results of that Test de-clared that variances of stocks to be not homogenous with respect to per-cent peewee, average egg weight, feed efficiency traits, percent small blood spots, percent meat spots and final body weight in the Seventeenth Test. In the Eighteenth Test the hypothesis of homogenity of stock var-iances was rejected with respect to percent peewee, small, medium eggs, average egg weight, percent blood and meat spots and percent mortality. Treatments variances were not homogenous with respect to percent peewee , percent small blood spots and percent large meat spots in the Seventeenth Test. In the Eighteenth Test, with respect to percent peewee eggs and percent small eggs, treatment variances were found to be not homogeneous. The third analysis conducted was the calculation of conventional product - moment coefficients of correlation among all traits studied. Sign and magnitude of the relationships between the traits showed great variation from treatment to treatment and from stock to stock, providing further evidence of differential response of stocks to variations in environment. Evidence for genotype-environment interaction in this study and in others is sufficient to Justify further research specifcally planned to demonstrate and measure such interaction but is not sufficient to formulate any definite and precise recommendations as to testing pro-cedures breeders should use.

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