THE EFFECT OF THIOURACIL ON EFFICIENCY OF GAINS AND CARCASS QUALITY IN SWINE 1

HE recent discovery of a series of drugs that will inhibit the formation of thyroid hormone by the thyroid gland makes it possible, by admin- istering such compounds, to determine the influence of subnormal levels of thyroidal activity on growth, fattening and carcass quality in various classes of livestock. Of the numerous compounds showing antithyroid properties, (Astwood, et al. ~943; Astwood, i943; and others) thiouracil seems to be one of the most suitable for this purpose because of its high potency and low toxicity. Kempster and Turner (i94~) reported that when o.2 percent thiouracil was fed to New Hampshire chicks for periods of I6 and 32 days beginning at io weeks of age the market grade was improved. In chicks fed thouracil from 6 to I4 weeks of age at levels of o.o2~ to 0.2 percent growth was re- tamed slightly, but market grade and fat deposition were signis ira, proved (Andrews and 8chnetzler, 194~). An increase in the rate of gain and a decrease in the feed required per unit of gain in older cockerels fed thiou- racil was reported by Mixner, Tower and Upp (1946). Glazener and Jull (I946) reported that in chicks started on thiouracil at 2 weeks of age growth and efficiency of gains were depressed and the fleshing was inferior. Muhrer and Hogan (i94~) comFared the gains and degree of fattening of hogs fed 0.2 percent thiouracil with that of pair-fed controls who~'e daily feed intake was restricted to that of the experimental group. It was reported that swine fed thiouracil for 28 days under these conditions were shorter and fatter than the controls and that they gained weight more rapidly and eco- nomically. However, use of the paired feeding system in this type of experi- ment tends to penalize the normal controls since their gains are necessarily depressed by limitation of their feed intake to that of the hypothyroid ani- mals. Consequently it seemed desirable to test the effect of thiouracil on swine fed ad libitum. It also seemed of considerable interest to obtain more objective measurements on the effects obtained on growth and carcass qual- ity than were available from the prior report.