EFFECTS OF FEEDING LOW AND HIGH GLUCOSINOLATE RAPESEED MEALS AND SOYBEAN MEAL ON THYROID FUNCTION OF YOUNG PIGS
In two experiments, 113 pigs were fed diets containing up to 25.3% low-glucosinolate, low-erucic acid rapeseed meal (cv. Tower = 00-RSM) or 31.3% commercially available rapeseed meal (C-RSM) as partial or complete replacements for soybean meal (SBM). The diets, formulated to be isonitrogenous and isocaloric, were fed ad libitum to the pigs from 4 to 10 wk of age. Serum triiodothyronine uptake (T-3 uptake) was greater (P < 0.05) in pigs fed the SBM diet compared with the other diets. In experiment 1, tetraiodothyronine (T-4) levels of 10-wk-old pigs fed the SBM diet were greater (P < 0.05) than pigs fed C-RSM or C-RSM + SBM diets. The free thyroxine index (T-3 uptake/100 × T-4) was lowest (P < 0.05) for pigs fed the C-RSM diet. In experiment 2, serum T-4 levels of pigs fed the SBM and 00-RSM + SBM diets were higher (P < 0.05) than for those of pigs fed other diets. Serum cholesterol levels of pigs fed the 00-RSM, C-RSM and C-RSM + SBM diets were higher (P < 0.05) than was found with the SBM or 00-RSM + SBM diets. Thyroid weight was greater (P < 0.05) in pigs fed the C-RSM or C-RSM + SBM diets. The height of epithelial cells was greater (P < 0.05) for pigs fed the 00-RSM and C-RSM diets and weight of epithelium of all pigs fed RSM indicated epithelial hypertrophy compared with those fed the SBM diet. The results suggested that thyroid function of pigs fed high levels of 00-RSM might be impaired compared with those fed SBM as the sole supplementary protein source in cereal-based diets, but less severely than with pigs fed C-RSM.