Comparison of Thyroxine Secretion Rate of Docile and Flighty Lines of Fowls.

Abstract

SummaryTwo strains of chickens developed by the Hy-Line Poultry Farms which were characterized by the terms as “docile” and “flighty” as to temperament were studied in regard to their estimated thyroxine secretion rate (TSR) during the summer (June). The “flighty” strain had a mean TSR of 0.82 μg L-T4/100 g bw/day whereas the “docile” strain had a mean TSR of 0.58 μg L-T4/100 g bw/day, a difference of 67.6%. In a second trial about one month later, during a period of elevated temperature 90μF (90-95°F), the TSR of the “flighty” birds was reduced to 0.58,μg/100 g bw, but the “docile” birds were unaffected. The percentage uptake of I131 by the “docile” birds was about 40% greater than the “flighty” birds indicating that the percentage uptake of I131 is not a good index of the functional activity of the thyroid gland. While previous studies indicated that L-T3 and L-T4 were approximately equal in biological activity in fowls, in this study, the two lines of birds showed L-T3 to be slightly over twice as acti...