THE EFFECTS OF TOWER AND MIDAS RAPESEED MEALS ON MILK PRODUCTION AND CONCENTRATIONS OF GOITROGENS AND IODIDE IN MILK

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Abstract
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.