Copper and iodine in pig diets with high glucosinolate rapeseed meal. II. Influence of iodine supplements for rations with rapeseed meal untreated or treated with copper ions on performance and thyroid hormone status of growing pigs

Abstract

In an experiment with 42 fattening pigs, supplementation of an 8% rapeseed meal (RSM) ration with 250 mg Cu together with I and Zn was tested. The RSM contained 0.25% isothiocyanates (ITC) and 1.37% oxazolidinethiones (OT) in the dry matter (DM). In a trial with 50 fattening pigs, untreated RSM (0.38% ITC; 1.19% OT in the DM) was compared to RSM treated with Cu 2+ (ITC and OT not detectable) and soya-bean meal (SBM). The RSM diets were supplemented with 0.0625–1.0 and the SBM diet (control) with 0.125 mg I kg −1. In addition to the supplementation of the RSM ration with I, Cu improved the performance and the thyroid hormone status. In comparison with the SBM control, RSM treatment with Cu 2+ resulted in a complete normalization of these parameters. Supplementation with Zn together with Cu and I had no additional effect. Only untreated RSM without I supplementation depressed performance and gave symptoms of I deficiency, but thyroid gland and liver weights were also increased and the serum T 4 content was significantly reduced in animals which were given the RSM not supplemented with I, but treated with Cu 2+. A plateau of the serum T 4 content was achieved from > 0.5 mg I kg −1 of the RSM diet. In contrast, when goitrogens were inactivated by means of Cu 2+, the serum T 4 level was increased significantly and plateaued from 0.122 mg I kg −1 diet. The present investigations show that rations with RSM should contain at least 0.5 mg I kg −1, but 0.1 mg I kg −1 is sufficient in diets without or with a low content of goitrogenic compounds.