The Effects of Tower and Midas Rapeseed Meals on Milk Production and Concentrations of Goitrogens and Iodide in Milk

Low glucosinolate Tower rapeseed meal (RSM), high glucosinolate Midas RSM and soybean meal (SBM) were compared in two separate 4 × 4 Latin squares with experimental periods of 35 days. Tower or Midas RSM was fed to lactating cows at 0, 5.7, 13.2 and 18.9% of the total diet (air-dry basis) and SBM was added to bring the protein level in the supplement for all diets to 18.9%. Replacement of SBM with Tower RSM resulted in a decrease (P < 0.01) in apparent digestibilities of crude protein and energy. Crude fiber and ether-extract digestibilities were not different. Daily digestible crude protein available decreased (P < 0.01) with higher levels of Tower RSM in the diet. Concentrations of thiocyanate in milk increased (P < 0.05) at all dietary levels of Tower and Midas RSM. RSM decreased (P < 0.05) the concentration of iodide in milk, with little effect due to Tower or Midas RSM or to level of RSM supplementation on the degree of milk iodide depression.