Abstract
The efficacy of a molybdate formulation and a zinc oxide bolus as prophylactic agents for enzootic icterus was evaluated in sheep. Before copper loading, liver biopsies were performed on 12 male, 6-month-old, Mutton Merino sheep to determine hepatic copper (Cu) and zinc (Zn) concentrations. The animals were restrictively randomised according to liver copper concentrations to 3 treatment groups (n = 4) to achieve similar mean liver copper concentrations per group. All sheep received 4 ml/kg of a 0.5 % aqueous solution of CuSO4 5H2O intraruminally 7 days per week for 10 weeks. On Day 0 the sheep in the Mo-group were injected subcutaneously with 42 mg molybdenum (Mo) contained in a commercial molybdate formulation. The animals in the Zn-group each received a zinc oxide bolus, containing 43 g zinc oxide, via a rumen cannula. Treatment was repeated on Day 42. Four animals served as untreated controls. Urinary copper excretion, plasma copper concentration, haematocrit and glutamate dehydrogenase (GLDH) activity were determined throughout the trial. The animals were sacrificed after 10 weeks and liver samples were submitted for histopathological examination. Liver and kidney copper and zinc concentrations were determined. Neither the molybdate treatment nor the zinc oxide boluses prevented hepatic copper accumulation. The urinary copper excretion, plasma copper concentration, haematocrit and GLDH activity were not significantly different (P > 0.05) from the controls.
Highlights
In the Karoo and southern Free State regions of South Africa a form of chronic copper poisoning, referred to as ‘enzootic icterus’ or ‘geelsiekte’, occurs in sheep under natural grazing conditions
The condition is extremely rare in sheep younger than 6-tooth, while clinical cases and mortality are most prevalent in old wornmouth animals[1]
The liver zinc concentrations decreased compared to the concentrations obtained at the start of the experiment in all the groups
Summary
In the Karoo and southern Free State regions of South Africa a form of chronic copper poisoning, referred to as ‘enzootic icterus’ or ‘geelsiekte’, occurs in sheep under natural grazing conditions. Many of the edible plants in these areas have copper concentrations exceeding 10 ppm dry mass (DM) and few plants have molybdenum concentrations above 0.5 ppm DM1. Ingestion of these plants over a number of years results in gradual hepatic copper accumulation[1]. Morbidity varies between 0.5 and 5 % of the flock and mortalaDepartment of Paraclinical Sciences, Faculty of Veterinary Science, University of Pretoria, Private Bag X04, Onderstepoort, 0110 South Africa. BDepartment of Production Animal and Community Health, Faculty of Veterinary Science, University of Pretoria.
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