Influence of Triiodothyronine on Feedlot Performance and Carcass Characteristics of Growing-Finishing Swine

Three experiments, involving a total of 147 pigs, were conducted to determine the effect of various levels and periods of administration of triiodothyronine on the weight gain, feed conversion, gland weights and carcass characteristics of growing-finishing swine. Weanling pigs were fed levels of 25, 50, 75, 125, 250 and 500 mg. triiodothyronine/ton of feed throughout the growing-finishing period. Pigs were also fed 50 mg. triiodothyronine commencing at 110 lb. and 150 lb. body weight. In one experiment a 14% protein ration was compared to a 21% protein ration. Results are as follows: Levels of 125 mg. and above appeared to be too high by virtue of a reduction in the efficiency of feed conversion. No consistent improvement in gains or feed conversion was elicited at levels of 25–75 mg., although in one instance a statistically significant improvement in gains (P<.05) was observed at a 50-mg. level of supplementation. Triiodothyronine supplementation tended to reduce the size of the thyroid gland, but appeared to have no affect on the size of the pituitary and adrenal glands. Carcass measurements revealed no significant effects due to triiodothyronine administration. Triiodothyronine effects were not significantly influenced by the protein levels studied. However, pigs fed 14% protein rations gained faster, converted feed more efficiently (P<.01), gave higher dressing percentages (P<.01) and were thicker in backfat (P<.01) than comparable pigs fed 21% protein rations.