Cadmium accumulation in liver and kidney of sheep grazing
ryegrass/white clover pastures
J. Lee, N.D. Grace, J.R. Rounce
AgResearch, Grasslands Research Centre, Private Bag 11008, Palmerston
North, New Zealand.
Proceedings of the New Zealand Society of Animal Production 1994,
54: 31-34
Pastures growing on soils fertilised with phosphatic fertilisers
accumulate cadmium (Cd) in their plant tops in proportion to substrate
concentrations. Sheep grazing pastures absorb some of this Cd. To quantify
the rate with which Cd is accumulated in sheep tissue, three replicated 0.4
ha blocks were fertilised with either 333 kg/ha of single superphosphate only
(control) or amended with CdSO4 to give 274g Cd/ha (high-Cd), and set stocked
with 10, three months old Romney wether lambs. Cadmium (Cd) concentrations were
determined in liver, kidney, proximal duodenal and skeletal muscle tissue of
sheep, ingesting either (means ± s.e.) 266±22 (control) or 746±58 (high-Cd) ug
CD/day from three to six months or 290±21 and 721±72 ug Cd/day over six to
eighteen months. Cadmium concentrations in kidney and liver tissue increased
markedly over the first three months: 0.042±0.006 to 0.32±0.03 (Control) and
0.57±0.04 (high-Cd) ug Cd/g fresh tissue, and 0.04±0.006 to 0.12±0.02
(Control) and 0.31±0.06 (high-Cd) ug Cd/g fresh tissue, for kidney and liver
respectively. Although total Cd content continued to increase, as organ size
increased, over the next 12 months daily accumulation rates in both tissues
were much lower compared with those over the first three months. For
example, daily Cd accumulation in kidney decreased from 0.25±0.002 to
0.06±0.01 and 0.47±0.04 to 0.32±0.05 (ugCd/d) for sheep from the control and
high-Cd pastures respectively. Total Cd content in kidney and liver combined
accounted for approximately 0.25% of total Cd ingested by sheep age three to
six months but this significantly decreased to 0.1% in sheep age six to
eighteen months.
At higher Cd intakes increased metallothionein protein synthesis in kidney and
liver tissue enabled animals to be more efficient in sequestering Cd. This
resulted in reduced accumulation of Cd in muscle tissue of sheep on the high-
Cd pastures (2.0±0.04 and 5.0±0.08 ng Cd/g) compared with those grazing the
control pasture (4.0±0.6 and 14±5 ng Cd/g) in animals from the first and
second periods respectively.
The results from this study show that it is the first few months after weaning
that fastest uptake into kidney occurs and therefore strategies to reduce Cd
absorption and subsequent accumulation, e.g. by increasing zinc in the diet,
should focus on young animals.
Keywords: NZSAPAB;
Cadmium; zinc; accumulation; sheep tissues; metallothionein.
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Last Updated 25-01-1997
