Masters Theses

Date of Award


Degree Type


Degree Name

Master of Science


Animal Husbandry

Major Professor

Eric W. Swanson

Committee Members

C. E. Wylie, M. C. Bell


The feeding of l-thyroxine, iodinated casein and similar substances to dairy cows to temporarily increase milk production is no longer in the experimental stage. Numerous investigators have amply demonstrated the galactopoietic activity of these thyroactive compounds. Widespread agreement exists among these many research workers that milk production can be increased in most cows through the feeding of these materials.The major portion of this work has involved the feeding of thyroprotein during the declining phase of one lactation. The behavior and response of a cow to this type of treatment is fairly well known. Not so well known, however, are the effects of the feeding of thyroactive materials in successive lactations to the same cows, or the comparative effects of different dose levels.

The study herein reported is divided into two parts. Experiment I was designed to study the effects of long-term feeding of thyroxine upon the milk production, milk composition, body weight, skeletal development and general health of those cows so fed. In this experiment five pairs of identical twin dairy cows were used. By feeding thyroxine to one of each pair, her mate then became the most nearly perfect control cow that nature can provide. By the use of identical twins any differences noted between the group fed thyroxine and the group handled normally would more accurately reflect the effect of the different treatments than would using unrelated cows no matter how closely paired as to size, age, milk production level and the other usual criteria for comparison.

The dose-level problem was studied in Experiment II by employing five different dosages of 1-thyroxine. These were 60, 80, 100, 120, and 140 mg. per day. It was hoped that an optimum dose level could be determined by varying intake of the drug in each cow.

By investigating these two particular phases of thyroxine feeding some helpful information might be secured on whether or not we can safely feed thyroxine year after year to the same cows and possibly how much of the material should be fed daily for optimum milk yield responses.

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