The status of cobalt in soil, plants and sheep in Shahrekord district, Iran

Cobalt (Co) deficiency occurs in many parts of world especially in tropical and subtropical countries.
Primary Co deficiency occurs only in places where the soil is deficient in Co. The type of soil and the presence of other substances like manganese and lime influence the absorption of Co (secondary Co deficiency). To determine the Co status in Shahrekord district, Iran, several important farms were selected and the Co concentration of 80 different soils (before cultivation) under cultivation of alfalfa, clover, barley and wheat and their cultivated plants (after full vegetative growing) were measured by atomic absorption spectroscopy. Moreover, blood samples were taken from 100 sheep fed the grown plants on those areas. The mean ± SD Co concentration in the soil of alfalfa, clover, barley and wheat farms were 0.14 ± 0.04, 0.16 ± 0.06, 0.10 ± 0.03 and 0.11 ± 0.05 mg/kg, respectively and the corresponding concentrations in plants were 1.32 ± 1.01, 2.2 ± 0.08, 1.2 ± 0.76 and 1.37 ± 0.88 mg/kg dry matter (DM), respectively. The mean ± SD Co concentration in sheep serum was 1.45 ± 0.41 μg/dl at various physiological conditions. Results indicated that in all studied areas, Co concentration in soil was lower than the normal range and primary Co deficiency was noticeable. On the other hand, Co concentration in different plants and ration was higher than animal demands, but serum Co was at marginal level and probably interfered with animal health. This study showed that the soils of lands under cultivation of clover and alfalfa and its related plants contained more Co than that of determined for barley (P<0.05). Furthermore, clover soil had higher amount of Co than wheat soil (P<0.05). There was a negative correlation between the amount of lead in soil of lands under cultivation of alfalfa and the concentration of Co in plants. Such a negative correlation was also detected between the amount of molybdenum and lead in soil and the concentration of Co in plants (P<0.05). Presence of some interfering factors in ration such as nitrogen (1.24 ± 0.3%), phosphorus (0.47 ± 0.18%), lead (2.87 ± 1.58 mg/kg DM) and molybdenum (0.1 ± 0.14 mg/kg DM) were negatively affected the uptake of Co and decreased serum Co concentration via secondary Co deficiency.