Date of Award


Document Type


Degree Name

Master of Science (MS)

Legacy Department


First Advisor

Donald M. Henricks

Second Advisor

D. E. Turk

Third Advisor

Farrell B. Brown


Throxine (T4) and triiodothyronine (T3) are hormones of the thyroid gland which are necessary for proper growth and development of animals. The physiological adjustments associated with thyroid hormone action are numerous and widely diversified. Most notable of the effects in mammals are control of basal metabolic rate, modification of net protein synthesis and activity of particular enyzme systems. This study was undertaken to study the relationship of thyroid status in the cow on administration of the anabolic steriod, trenbolone acetate. Three groups of yearling heifers were fed a measured amount of a fattening ration for 127 days. One group severed as controls and received no implant, one group was implanted with 300 milligrams of trenbolone acetate for 99 days, and one group recieved an identical impant for 62 days. Weight gain, feed conversion efficiency, and thyroid status were determined for the animals in in each treatment group. Total T4 and T3 concentrations were determined in all blood samples for the four heifers in each group. Free T4 concentrations were determined in selected plasma samples for each heifer during the four distinct periods of the experiment. Period 1 was a pretreatment period for all groups, periods 2 and 3 represent the time the implant was in place in the long term group, period 3 represented the treatment period for the short term group and period 4 was a posttreatment period for all groups. Attempts were made to correlate thyroid status as judged by free T4 analysis to rate of weight gain for the heifers. A different reponse was seen in the two implanted groups with respect to thyroid status and weight gain. In those animals with repect to thyroid status and weight gain. In those animals where significantly improved growth (P<.05) was seen (short term group), significantly lower (P<.05) free T4 concetrations were also seen. Free T4 concentrations in the 99 day implant group were not different from controls during any period of the experiment. The rate of weight gain for these two groups was also not different.