Abstract
In northern Sweden, 23 heifers out of 98 cattle died of acute vanadium toxicity in a 10-day period. Eight months earlier a pasture had been fertilized with basic slag, containing 3% vanadium. The fertilizer was laid on the surface without being ploughed in. Mainly heifers, and some cows, were fed with basic slag-contaminated fresh hay. The first signs of illness appeared 11 days later, and the first case of death appeared 14 days after the initial clinical signs. The signs were diffuse and difficult to interpret. Inappetence, black diarrhea, lethargy, dehydration and spontaneous abortions occurred. Further, pulmonary lesions, conjunctivitis, neurological disturbances such as depression, leg incoordination, and paralysis of the hind limbs and face were also noted. Although feeding with the contaminated hay was stopped at the outbreak of the toxicity, the 23 animals died or had to be slaughtered, and at necropsy of another heifer 4 weeks later, large amounts of basic slag were still found in the alimentary tract. High vanadium concentrations were found in the liver, kidneys, spleen and urine, 5.9, 5.5, 1.9 and 4.8 mg/kg w.w., respectively. In bone tissue (coccygeal vertebrae), the highest value in an acutely poisoned heifer was 0.680 mg/kd d.w., in the same range as that of an experimentally poisoned sheep. Surviving heifers were more affected than cows; the state of health of these heifers gradually deteriorated and, therefore, a few were slaughtered 3 months later. Because of residual neurological disturbances and decreased milk production, the rest of the herd was slaughtered 5 months after the outbreak, and samples were collected and analyzed. Elevated vanadium concentrations were found in the organs, especially in the spleen, where values of 1.40 and 1.42 mg/kg w.w. were found in 2 heifers at 3 months. The values in heifers (n = 6) were decreased 5 months after the outbreak. The median concentrations were somewhat higher in the liver than in the spleen, and lowest in the kidney (0.244, 0.213 and 0.058 mg/kg w.w., respectively). In the organs of the cows (n = 24), which were less exposed, the corresponding values were 0.012, 0.095 and 0.013 mg/kg w.w., respectively. Vanadium concentrations were also determined in livers of cows and calves at regular slaughter in four geographic regions of Sweden. In one of the regions, where basic slag (with 3% vanadium) had been used for many years, the values were significantly higher than those in the other regions. In a material of 293 specimens, an upper reference limit of 0.012 mg/kg liver w.w., with a 90% confidence interval of 0.011-0.019 mg/kg w.w., was found to be normal for cattle in Sweden. Concentrations above the Highest Swedish Reference Value, 0.019 mg/kg liver can be considered elevated. Vanadium-containing basic slag used as fertilizer caused poisoning in a herd of cattle and its regional use was detectable in livers from cattle at regular slaughter. Such fertilizer must be applied in a proper way. It should be ploughed in and any direct contact of grazing animals with the hazardous fertilizer should be prevented.
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