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Response of Hyperthyroid, Euthyroid and Hypothyroid Lambs to Exogenous Thyroxine^{1, 2,}

University of Wyoming, Laramie 82070⁴

Abstract

Forty-eight wether lambs representing three thyroid classification levels and four thyroxine implantation levels within each thyroid level were fed a finishing ration for a 72-day period. There were no significant differences in total weight gains, pre-slaughter shrink, cooler shrink, percent kidney fat, width of carcass leg, carcass grade, fat thickness over the 12th rib, longissimus area, tenderness score and percentages of fat, bone and lean as determined by physical separation of the right rack due to thyroid or implant level. A composite sample of the left rack was subjected to chemical analyses. There was a significant interaction between thyroxine implant level and thyroid activity level on percent carcass fat. There were no significant differences in the percent of carcass protein as a result of implant level, thyroid activity or interaction between these variables. The percentage of carcass water varied significantly due to implant level, thyroid status and breed. Significant differences in thyroid activity by blood analyses were noted at the beginning of the experimental period. After 1 week post-implant, the implanted lambs exhibited a significantly greater thyroid activity when compared with non-implanted lambs. At 4, 6 and 8 weeks post-implant, the hyperthyroid-classified lambs exhibited a significantly greater degree of thyroid activity when compared with the euthyroid- and hypothyroid-classified lambs.

¹ Data reported here were taken from a thesis submitted by the senior author in partial fulfillment of the requirements for the Ph.D. degree, University of Wyoming.

² The authors wish to acknowledge the cooperation of Abbott Laboratories, North Chicago, Illinois, for furnishing the resin-embedded sponges and I-131 buffer solution.

³ Present address: University of Nebraska, Scotts Bluff Station, Mitchell.

⁴ Approved by the Director of the Wyo. Agr. Exp. Station as Journal Paper No. 451.