EFFECTS OF FEEDING A CONCENTRATE CONTAINI NG DOUBLE LOW RAPESEED MEALON FERTILITY AND METABOLIC STATUS OF DAIRY-COWS

The effects of feeding a concentrate with 30% double low rapeseed meal to 110 dairy cows in an area of relative iodine deficiency were studi ed. Total glucosinolate concentration in the rapeseed meal was determi ned by 13 mu mol/g fat free material, 5-vinyloxazolidine-2-thione 611 mg/kg and allylisothiocyanate 124 mg/kg. Thyroid function, fertility a nd milk production were measured No adverse effects on these were obse rved during the 10 month experimental period The dietary iodine intake was determined to be fully sufficient (0.71 to 1.12 mg per kg dry mat ter). No problems occurred with respect to the acceptance of the rapes eed meal as compared to the control group. Thyroid function was not in fluenced by feeding the rapeseed diet. Thyroxine concentration in seru m was significantly correlated to milk performance in the experimental and control groups. Rapeseed feeding significantly increased thiocyan ate concentration in serum and milk, but in individual milk samples in no instance the concentrations exceed 9.7 mg/l and therefore were in the safe range for human consumption. Iodine concentration in milk of experimental cows was slightly lower than in the control group. Milk p erformance was not impaired in the rapeseed-fed animals. Milk protein concentrations were significantly higher in the experimental group. Th e fertility status, using all indices tested, was unaffected by the fe eding of rapeseed meal, except the herd index of Britt and Ulberg. No puerperal problems occurred. First oestrus after calving started earli er in the experimental group, as determined by milk progesterone estim ations. The results of this study indicate that the feeding of double lows rapeseed meal at an inclusion rate 30% is safe, provided the nutr itional iodine intake exceeds 10 mg per cow per day and the daily gluc osinolate intake is below 50 mmol per cow and day.