Chronic copper poisoning in sheep grazing pastures fertilized with swine manure

Several pregnant ewes developed an acute hemolytic crisis and died. Liver and kidney copper concentrations were high, confirming chronic copper poisoning as the cause of death. Feed and water samples that the affected ewes had been consuming did not contain excess copper. Because swine manure slurry had been applied to the pasture where the sheep had grazed, a copper analysis was conducted on soil and forage samples from this field. High copper concentrations were detected in the soil and forage samples from the slurry pasture. Most sheep producers are aware of the catastrophic consequences that result when feeds containing copper and insufficient amounts of molybdenum are fed to sheep. However, producers and veterinarians often are unaware of some of the subtle sources of copper. Most of the copper that is added to swine and poultry feeds as growth promotants passes through the gastrointestinal tract unabsorbed and remains in the waste material. Pastures that have copper-containing waste material, but no molybdenum applied, can produce the same fatal results as giving sheep feed supplemented with copper but containing no molybdenum.     

Long-term observation of subclinical chronic copper poisoning in two sheep breeds

Fourteen castrated male sheep of two breeds, the Mutton Merino (MMB) and Blackhead Suffolk cross breed (BSC), were exposed to an oral copper (Cu) intake of 3.7 mg/day per kg body weight for 84 days (high Cu group, HCu), and 11 castrated male sheep received a daily oral Cu intake of 0.16 mg/day per kg body weight (controls). Liver Cu concentration was measured in liver biopsies until 2.7 years after Cu overdose. Haematologic parameters, plasma Cu, enzymes and metabolites were analysed and post-mortem examinations were carried out. No haemolytic crises occurred. The highest liver Cu concentrations (133-677 mg/kg wet weight) were measured in HCu sheep around day 110 with significantly higher values in BSC than in MMB. The very slow decreases of liver Cu concentration of HCu sheep after day 215 showed individual half-life periods of 175 +/- 91 days. A progressive Cu retention in the liver of HCu sheep during Cu supplementation indicates strong Cu binding and storage in the liver. High values of glutamate dehydrogenase (20-940 U/l) measured frequently until day 700 and a diminished plasma clearance of bromosulphthalein as well as pathohistological findings of focal liver necrosis confirm the markedly chronic character of Cu poisoning.     

Phosphatic fertiliser poisoning of sheep: Experimental studies

The toxicity of serpentine phosphate and superphosphate for non-pregnant dry ewes, pregnant ewes and lactating ewes was investigated by oral dosing. An attempt was made to reproduce a natural episode of poisoning by exposing pregnant and lactating ewes to topdressed pasture.

A total dose in the range of 1200 to 1800 g of serpentine phosphate was required to kill two ewes and it was concluded that natural episodes of poisoning with this material are unlikely. The toxic process was similar to that caused by superphosphate.

The LD₅₀ of superphosphate was estimated to be in the range of 5 to 6 g/kg and a dose in the range of 200 to 300 g was sufficient to kill most sheep. The apparently greater susceptibility of pregnant and lactating sheep to poisoning suggested by the study of natural outbreaks was not demonstrated in these experiments, but the numbers of experimental animals may have been too small to detect diiering susceptibility.

The clinical disease resembled that seen in natural episodes; anorexia, diarrhoea, progressive depression and death in a period of 5 to 8 days after the start of dosing. Sublethal doses produced a transient diarrhoea and, in two sheep, a severe wool-break.

The principal biochemical changes were hyperphosphataemia and evidence of renal failure (oliguria, uraemia, azotaemia). Gross lesions were not consistently present but included abomasal ulceration and renal cortical swelling and pallor. The histopathological evidence of renal tubular obstruction by flocculant eosinophilic casts was characteristic.     

Use of ammonium tetrathiomolybdate in the treatment of copper poisoning in sheep

Intravenous administration of ammonium tetrathiomolybdate (three doses on alternate days) appeared to be an effective means of containing the acute phase of copper toxicity in sheep, whether this arose from continuous ingestion of high copper feeds or by injudicious use of copper preparations for the control of copper deficiency. No adverse effects were recorded on lamb numbers, birth weight or survival of lambs born to ewes of normal to low copper status when the treatment was applied at sensitive periods of the reproductive cycle. Decreases in 'available' plasma copper and in liver damage occurred rapidly in response to intravenous tetrathiomolybdate and it is suggested that all animals at risk be treated.     

Acorn poisoning in sheep

Abstract

Extract

Robins and Shapcott (1954 Robins, J. H. and Shapcott, R. 1954. N.Z. vet. J., 2: 55–55. [Taylor &; Francis Online] , [Google Scholar]) recorded cases of presumed acorn poisoning in sheep.