Dietary Thyroprotein Influence on Lamb Performance and Blood Constituents

Abstract

Two trials were conducted to study the influence of dietary thyroprotein (Protamone) on lamb performance and blood constituents. In the first trial, 60 lambs averaging 27 kg initially, were fed 0, .04, .08 and .12% thyroprotein in all-concentrate diets ad libitum for 56 days. Daily thyroprotein intakes were 0, .26, .88 and 1.35 g for lambs fed diets 1, 2, 3 and 4, respectively. Average daily gains were .23, .16, .18 and .16 kg for lambs fed diets 1 through 4, respectively. Thyroprotein consumption produced higher plasma free fatty acid, but lower plasma cholesterol concentrations than did the control diet. Plasma urea nitrogen levels were lower when thyroprotein was fed. Trial II was conducted to observe the effects on lamb performance and blood constituents of withdrawing thyroprotein from the diet. Thirty-six lambs, weighing 33 kg initially, received either 0, 1.2 or 1.6 g of thyroprotein per head per day for 30 days, after which thyroprotein was removed from the diets of all Iambs. Lambs receiving thyroprotein for the first 30 days of the trial gained slower than those receiving the control diet. However, when dietary thyroprotein was removed for the last 28 days, those lambs which had previously consumed thyroprotein gained significantly faster than those consuming the control diet throughout the trial. Removal of thyroprotein from the diet also caused a significant reduction in plasma free fatty acid concentrations. Plasma cholesterol tended to decrease after removal of thyroprotein from the diet, whereas plasma urea nitrogen levels were lowest when thyroprotein was being consumed. These data indicate that mild hyperthyroidism does not stimulate growth in young lambs. Copyright © 1976. American Society of Animal Science . Copyright 1976 by American Society of Animal Science.