Evaluation of a commercially available molybdate formulation and zinc oxide boluses in preventing hepatic copper accumulation and thus enzootic icterus in sheep

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.     

The retention and efficacy of soluble-glass boluses for providing selenium, cobalt and copper to sheep

The efficacy and retention of prototype and commercial (Cosecure) soluble-glass boluses containing selenium, cobalt and copper and having a similar size, density and composition were evaluated in separate 12-month trials with sheep grazing low selenium pastures but with adequate cobalt and copper levels. In both trials, sheep confirmed by X-ray as containing a bolus grew at a significantly greater rate than control sheep. This was attributed to the correction of a selenium deficiency. Although liver copper, and liver and serum vitamin B12 levels were significantly greater in treated sheep than controls on some occasions, the differences were not as great or consistent as with blood selenium levels. The rate of bolus loss was high and in both trials, approximately 40% of the sheep had lost the bolus after 6 months. No prototype boluses were present after 12 months. Intact Cosecure boluses were recovered from 3 sheep out of 30 after 12 months whilst one animal contained a part bolus. The recovered boluses were approximately 45% lighter than when originally administered. Bolus loss did not appear to be due to complete dissolution. In sheep which had lost the bolus, blood selenium levels fell with a half-life of 43 +/- 10 days.     

Renal lesions and tissue concentrations of zinc, copper, iron and manganese in experimentally zinc intoxicated sheep

Renal lesions were produced in three out of 10 sheep dosed with large quantities of zinc for two to 14 weeks. Administration of the zinc resulted in significant increases in the concentrations of zinc in the kidneys, liver and pancreas, and of copper and iron in the kidneys and pancreas, and a significant decrease in the concentration of manganese in the pancreas. The sheep with kidney damage had increased plasma creatinine concentrations and significantly higher mean concentrations of zinc in their livers and pancreases, and of copper and iron in their kidneys, than the sheep with no kidney damage.     

Failure of orally administered zinc to prevent experimentally induced footrot in sheep

Two groups of adult Merino sheep, initially grazed on pasture, were dosed daily with zinc sulphate (1 mg Zn/kg LW) or zinc oxide (15 mg Zn/kg LW) for six and seven weeks, respectively. On the 18th day, both groups were transferred to indoor pens together with unmedicated control sheep, and five days later the feet of all animals were infected artificially with a virulent strain of Bacteroides nodosus. By the fourth week after challenge, 85% or more of the feet challenged had developed advanced footrot, and no significant differences in the incidence and severity of lesions between dosed and un-dosed groups were recorded. Plasma zinc concentrations, monitored throughout the experiment, remained at similar levels in sheep receiving the lower dose rate and in the controls. At the higher dose rate, plasma zinc levels increased till Day 23, but thereafter declined to values comparable to those of undosed animals. At post mortem, no evidence of zinc toxicosis was found, and only the kidneys of sheep receiving the higher dosage showed a significant accumulation of zinc compared with the controls.     

Failure of oral zinc therapy to alleviate Bacteroides nodosus infections in cattle and sheep

Cattle and sheep with Bacteroides nodosus infection were treated orally with both high (65 mg Zn/kg and 82 mg Zn/kg) and low (1 mg Zn/kg and 8.6 mg Zn/kg) doses of zinc sulphate respectively. The lower dose rates administered weekly for one month, in the case of cattle, or daily for 2 weeks, in the case of sheep, had no effect either on serum zinc levels or the prevalence or severity of infection in treated animals. High dose rates of zinc (approximately 2.5 g Zn per head per day) were required to elevate serum levels above those normally present in both cattle and sheep. Even these dose rates continued daily for about 2 weeks had no beneficial effect on B. nodosus infection in either species.     

Treatment of ovine virulent footrot with zinc sulphate/sodium lauryl sulphate footbathing

Trials were conducted on 2 commercial sheep flocks in the Gippsland region of Victoria to determine the efficacy of treating ovine virulent footrot by footbathing in aqueous zinc sulphate solution (20% w/v). The effects of foot paring, parenteral penicillin, vaccination and addition of sodium lauryl sulphate (SLS) to the footbaths were assessed. Trial 1 comprised 297 sheep with an initial prevalence of footrot of 33% and most lesions were severe and chronic. Treatment of sheep with unpared feet by zinc sulphate footbathing for 1h did not result in a significant reduction in footrot prevalence (n = 120, cure rate 33%) whereas a significant (P less than 0.01) response was obtained by footbathing for 1h with zinc sulphate/SLS (n = 120, cure rate 55%). Trial 2 comprised 1,042 sheep with a pretreatment footrot prevalence of 71% and predominantly severe lesions. In this flock all treated sheep were footbathed in zinc sulphate/SLS for 1h on 2 occasions, 5 days apart and the effects of additional surgical and parenteral treatments were assessed. Foot paring had a significant detrimental effect on cure rate (P less than 0.01). The administration of procaine penicillin at the time of the first footbathing with zinc sulphate/SLS made no significant improvement to the rate of cure. Footrot vaccine given 8 and 2 weeks prior to footbathing did not cure significantly more sheep than footbathing alone, but the results were significantly better than from foot paring plus footbathing, and from combined foot paring, footbathing and parenteral penincillin treatment (P less than 0.01). The cure rate was 84% for sheep that were only footbathed, 72% for those foot pared and footbathed, 72% for those foot pared, footbathed and given penicillin, and 88% for those vaccinated and footbathed.     

The ubiquitous role of zinc in health and disease

Objective – To review zinc physiology and pathophysiology and the importance of zinc toxicity and deficiency in veterinary patients.
Data Sources – A review of human and veterinary medical literature.
Human Data Synthesis – There is a significant amount of original research in humans and animals on the role of zinc in multiple organ systems. There is also significant data available on human patients with zinc abnormalities.
Veterinary Data Synthesis – Zinc deficiency has been studied in dogs with genetic disease and dietary deficiency leading to dermatological disease and immune deficiency. Zinc toxicity has been described after ingestion of metallic foreign bodies containing zinc.
Conclusions – Historically, the role of zinc in health and disease has been studied through patients with toxicity or severe deficiency with obvious clinical signs. As the ubiquitous contribution of zinc to structure and function in biological systems was discovered, clinically significant but subtle deficiency states have been revealed. In human medicine, mild zinc deficiencies are currently thought to cause chronic metabolic derangement leading to or exacerbating immune deficiency, gastrointestinal problems, endocrine disorders, neurologic dysfunction, cancer, accelerated aging, degenerative disease, and more. Determining the causal relationships between mild zinc deficiency and concurrent disease is complicated by the lack of sensitive or specific tests for zinc deficiency. The prevalence of zinc deficiency and its contribution to disease in veterinary patients is not well known. Continued research is warranted to develop more sensitive and specific tests to assess zinc status, to determine which patients are at risk for deficiency, and to optimize supplementation in health and disease.     

Failure to eradicate ovine footrot associated with Dichelobacter nodosus strain A198 by repeated daily footbathing in zinc sulphate with surfactant

OBJECTIVE: To investigate the effect of repeated daily footbathing in zinc sulphate on virulent ovine footrot associated with S1, U1 and U5 zymogram types of Dichelobacter nodosus, including the highly virulent S1 strain A198. DESIGN: A field trial with experimentally infected sheep. PROCEDURE: At week 0, 50 sheep were infected with D. nodosus strains A198 (S1), C305 (U1), BC3993 (U5) and BC3995 (U5). At weeks 1 and 47, respectively, 169 and 235 uninfected sheep were added. At week 60, sheep were allocated to control and treatment groups each containing 220 sheep. Every 2 or 4 weeks to week 113, feet were inspected, and lesions were scored and sampled. Treatment sheep were footbathed in 15 to 18% (w/v) zinc sulphate with surfactant for 5 consecutive days (10 min per day) during week 61. During week 110, the footbathing protocol was applied again, this time to all surviving treatment and control sheep. RESULTS: BC3993 and A198 were isolated from 57% (162 of 285) and 20% (58 of 285), respectively, of new lesions sampled between weeks 3 and 13, and 21% (57 of 271) and 50% (136 of 271) between weeks 49 and 59. Percentages of new lesions associated with C305 and BC3995 remained constant. During the initial 17 weeks after footbathing at week 61, 90% (75 of 83) and 19% (95 of 490) of lesions in treatment and control sheep, respectively, were score 4 or 5, and 94% (47 of 50) and 38% (33 of 87) of those were associated with A198. CONCLUSIONS: Repeated daily footbathing did not eradicate virulent ovine footrot because strain A198 produced deep, covert lesions that facilitated the survival of D. nodosus.     

Comparison of three methods of thiamine supplementation by measurement of urinary thiamine excretion in sheep

The relative efficacy of thiamine supplementation to sheep by injection, subcutaneous implant and orally administered protected thiamine bolus was compared in two experiments using a grass and hay ration and a ration containing bracken rhizomes to induce thiamine deficiency. In both experiments, urinary excretion of thiamine was significantly higher in supplemented sheep than in the controls, and in sheep supplemented by injection than in sheep supplemented by implant or protected boluses. Thiamine excretion was lower in sheep fed the ration containing bracken rhizomes than in sheep fed the grass ration.     

Eradication of ovine footrot by repeated daily footbathing in a solution of zinc sulphate with surfactant

OBJECTIVE: To investigate the effect on ovine footrot of repeated daily footbathing in a solution of zinc sulphate with surfactant. DESIGN: Merino sheep were allocated to control and treatment groups of 119 sheep each at week 0. The sheep had a history of S1, U1, T and/or U6 types of Dichelobacter nodosus in interdigital and underrunning footrot lesions. Feet were not pared prior to treatment. PROCEDURE: Treatment sheep were footbathed in a 15 to 18% (w/v) solution of zinc sulphate with surfactant for 10 min on five consecutive days during week 1. At week 2, and fortnightly to week 52, all feet were inspected, lesion scores were recorded and samples were taken for laboratory tests. At week 53, all feet with no lesions at week 52, but with underrunning lesions prior to week 1, were pared and samples were taken. RESULTS: After footbathing, there were no lesions in any treatment sheep at any inspection to week 52. The percentage of feet of control sheep with lesions increased from 9% (391 of 4,284) between weeks 20 and 36, to 14% (593 of 4,284) between weeks 36 and 52. Ninety-five of 96 control sheep with no lesions at week 20 were still asymptomatic at week 52. D nodosus was not isolated from samples taken from 99 and 87 pared feet of treatment and control sheep, respectively. CONCLUSION: Repeated daily footbathing combined with prolonged exposure to a dry environment eradicated footrot in sheep with both interdigital and underrunning lesions in feet that were not pared prior to treatment.     

Comparison of a novel form of zinc with zinc oxide bolus licensed for prevention of facial eczema,and interaction with copper oxide in sheep

To evaluate a novel elemental zinc bolus compared with a registered positive control zinc oxide bolus and assess serum zinc concentrations following concomitant treatment with a capsule containing copper oxide needles. Forty Romney-cross ewes were randomly allocated in a 2 × 2 factorial design study. On Day 0, 20 ewes received novel boluses containing elemental zinc (Investigational Veterinary Product, IVP) while 20 received a zinc oxide bolus (control; CP). Half the animals in each zinc treatment group (n = 10) were treated with a copper oxide needle capsule [Copasure® - Ewe]. Weekly, from Day −7 to 56, all ewes were assessed for signs of photosensitization, and for 10 ewes from each zinc treatment groups, samples were collected for analysis of serum GGT activity, serum zinc concentrations, faecal zinc concentrations and on Days −7 and 56, liver copper concentrations. Multivariable random-effects models assessed the effects of zinc treatment, copper treatment, treatment interactions and time on all analytes. Regression models examined associations between serum and faecal zinc concentrations and GGT activity. Low spore numbers indicated low Pithomyces chartarum challenge. Serum zinc levels were significantly higher in the IVP than in the CP group [p < 0.0001] and varied by time [p < 0.001] and positively associated with faecal zinc concentration [p < 0.001]. Copper treatment did not affect serum zinc [p = 0.82] or faecal zinc [p = 0.92] concentrations. Liver copper concentrations did not differ between zinc treatment groups on Day −7 [p = 0.6] or Day 56 [p = 0.95]. Only the CP/no copper group had no increase in liver copper concentrations.     

Interaction between copper and zinc in sheep parenterally treated with zinc oxide

Changes in copper and zinc concentrations in the blood serum of sheep were studied in clinical conditions for sixty days in relation to the intramuscular application of zinc oxide at a dose of 10 mg Zn per kg liveweight; zinc oxide was administered in a developmental preparation. Serum concentrations of zinc started increasing significantly the eighth day after administration (p less than 0.01), the maximum values were found out on the twelfth day (21.19 +/- 3.89 mumol X l-1). Significantly higher concentrations of zinc in the blood serum of test sheep were observed as soon as on the eighth day (p less than 0.01), in comparison with the untreated group, and they persisted till the end of investigation (p less than 0.01). Simultaneously with the changes in serum zinc concentrations, copper metabolism was influenced when the statistically higher values of copper concentrations in the blood serum of the test group were recorded the eighth and twelfth days (p less than 0.01), in comparison with the control animals. In the remaining period, serum copper concentrations did not show any mathematical dependence and the equalization to the original values in the treated group occurred at the end of the experiment. The above-mentioned results from the sheep treated with zinc oxide refer to a possibility of influencing mutually the copper and zinc metabolism also parenterally; this could be utilized during the treatment of secondary deficiencies, or toxicosis.     

Hepatic activity of 3-hydroxy-3-methylglutaryl-CoA reductase in rats with alimentary zinc deficiency

Recent studies demonstrated that zinc deficiency lowers hepatic cholesterol concentrations in rats fed on diets that were rich in polyunsaturated fatty acids (PUFA); in contrast, in rats fed on diets that were rich in saturated fatty acids, zinc deficiency did not influence hepatic cholesterol concentrations (Eder and Kirchgessner 1993, 1994a,b, 1995). To date the mechanism underlying those effects is unclear. Based on ¹⁴C-incorporation into tissue lipids, a study by Patel et al. (1975) suggested that zinc deficiency impairs the hepatic synthesis of cholesterol. However, their investigation did not include studies on enzymes involved in cholesterol synthesis. The present study therefore was focused on the effects of zinc deficiency on the activity of hepatic 3-hydroxy-3-methylglutaryl-CoA reductase (HMG-CoA reductase) which is the key enzyme in the regulation of cholesterol biosynthesis. Therefore, rats were fed zinc-deficient diets containing either linseed oil or olive oil as sources of fat, and the activity of HMG-CoA reductase was assayed in hepatic microsomes.     

The effect of lupinosis on liver copper, selenium and zinc concentrations in merino sheep

Merino wether weaners were exposed to toxic lupin stubbles for periods of one, two and six to nine weeks, and the effect on their liver copper, selenium and zinc concentrations studied. After the one week period there was a slight decrease in liver copper and selenium concentrations in sheep severely affected with lupinosis. This was attributed to loss of these elements from necrotic cells, and greatly increased quantities of fat in the liver. In the same period liver zinc concentrations declined and were negatively correlated with the degree of liver injury. After two weeks or more of exposure to toxic lupins a positive correlation existed between both the liver copper and selenium concentrations, and the degree of liver injury. Furthermore, total liver copper and selenium levels were also positively correlated with the degree of liver injury. Liver zinc concentrations were negatively correlated with the degree of liver injury. It is suggested that when the liver is under the influence of the toxins causing lupinosis for more than two weeks, it stores copper and selenium, and loses zinc.     

The protective effect of zinc sulphate in experimental sporidesmin poisoning of sheep

Aqueous solutions of zinc sulphate were administered orally to sheep over 5 days (0.125, 0.5 and 2.0 g Zn⁺⁺/sheep/day) to bracket a 3-day period during which sporidesmin also was dosed. The zinc sulphate treatment gave protection from the effects of sporidesmin when compared with control groups dosed sporidesmin alone. Body weight changes were improved and liverdamage scores, numbers of animals showing photosensitisation, serum levels of glutamic oxaloacetic acid transaminase and total bilirubin were lower. The protective effects of zinc sulphate were obtained at levels well abovethose required for growth and maintenance. Protection increased but at a diminishing rate with increasing dose rate of zinc. Because of the small safety margin which exists between the dose rate of zinc sulphate which will provide adequate protection and that which will cause toxicity the use of zinc for the control of facial eczema is not recommended.     

Trace elements in grass, cattle liver and sheep liver from districts surrounding Karatina, Kenya. II. Copper, molybdenum, zinc and sulphur

Thirty-one samples of pasture grass from districts surrounding Karatina, Kenya were analysed for contents of copper, molybdenum, zinc and sulphur. The following mean values and standard deviations were found: Copper: 8.2 +/- 5.0 mg/kg DM; molybdenum: 1.4 +/- 2.6 mg/kg DM; zinc: 33 +/- 10 mg/kg DM and sulphur: 0.17 +/- 0.06% DM. Mean value of the ratio between copper and molybdenum was 13 +/- 11. Samples of cattle liver (n = 96) and sheep liver (n = 93) were analysed for copper and zinc with the following results: Cattle liver: 21 +/- 16 mg Cu/kg WW and 37 +/- 11 mg Zn/kg WW. Sheep liver: 59 +/- 37 mg Cu/kg WW and 30 +/- 6.4 mg Zn/kg WW. It is concluded that subclinical copper deficiency may occur in cattle in the districts included in the investigation. The copper status of sheep seems to be adequate. The levels of zinc may indicate a marginal intake of this element in sheep.     

Effects of zinc levels on activities of gastrointestinal enzymes in growing rats

The present study investigated the effect of different zinc (Zn) levels on activities of gastrointestinal digestive enzymes of growing rats. Four diets including Zn‐adequate (ZA; 46 mg/kg, control), Zn‐deficient (ZD; 3 mg/kg), high Zn supply (ZH; 234 mg/kg) and pair‐fed in which animals received the ZA diet at restricted amounts reflecting feed intake of the ZD group were fed to rats for 5 weeks. Dietary Zn was supplemented with ZnO. The results showed that Zn deficiency resulted in decreases in body weight, while ZH supply stimulated growth. The activities of sucrase, lactase and lipase were unaffected by dietary Zn levels. Maltase activity, however, was reduced in ZD group and elevated in ZH group. Amylase and protease activities were depressed by zinc deficiency. However, rats fed the Zn‐repletion diet displayed higher activity of pepsin, pancreatic amylase and protease. In particular, ZH supply did have no effect on intestinal hydrolases activities. The present study suggested that zinc deficiency impaired the activities of digestive enzymes and growth of animals. However, ZH supply might improve the digestion of nutrients via increasing activities of gastrointestinal hydrolase and probably enhanced animal health.     

Settling of insecticide from dip wash mixed with dam water and zinc sulphate and used to control sheep lice (Bovicola ovis)

SUMMARY Insecticidal dipping fluid emulsions, mixed in vitro in dam water containing suspended clay particles and 1% w/v zinc sulphate, were analysed to determine rates of settling of diazinon, cyhalothrin and cypermethrin. Fifteen minutes after mixing, the concentration of the insecticides 5 cm below the surface had declined by 72.5%, 72.8% and 89.4%, respectively. On remixing, the concentration of insecticide in suspension was close to or greater than the initial concentration. In 2 trials, lice were eradicated from sheep showered with dip wash mixed in cloudy dam water to which 1% w/v of zinc sulphate was added. In 12 flock treatments in which 1000 to 2000 sheep were dipped with added zinc sulphate, the concentration of insecticide remained above the minimum lethal for susceptible strains of lice. However, lice were still present 6 months later in 8 of these flocks. When zinc sulphate is added to dip wash, agitation is needed to maintain the insecticide in suspension.     

Influence of variable content of dietary zinc on copper metabolism of weanling foals

The influence of variable zinc content (29.1, 250, 1,000 and 2,000 mg/kg of dry weight) in a basic diet containing 7.7 mg of copper/kg on the ability of weanling foals to maintain normal copper balance was investigated. Serum copper and zinc concentrations were monitored, and terminal hepatic copper and zinc contents were measured in 4 weanling foals fed the basic diet containing 29.1 mg of zinc/kg and in 2 foals each fed the higher-zinc diets. Foals fed the lower-zinc diets (29.1 and 250 mg/kg) maintained normal serum copper and zinc concentrations for 14 to 15 weeks, whereas those fed the 2 higher-zinc diets became hypocupremic within 5 to 6 weeks and were lame within 6 weeks, owing to cartilaginous disease characteristic of osteochondritis dissecans. Serum zinc concentration in the foals fed the 2 higher-zinc diets increased to greater than 2 micrograms/ml within 2 weeks. Foals fed the high-zinc diets became lame after serum copper concentration had remained at 0.3 micrograms/ml for greater than 1 week. Serum copper concentration in these arthritic foals was less than or equal to 0.2 micrograms/ml at the end of the study. In lame foals, fractures of the cartilage of the articular and growth physes occurred through the zone of hypertrophic cells, and varied from bilateral to unilateral and from small to large. Free masses and flaps of cartilage attached to one side were numerous.     

Further evidence that zinc sulphate compromises the efficacy of dipping treatments using diazinon to control sheep lice (Bovicola ovis)

Objective To compare the wettability and efficacy of diazinon dip wash made with and without the addition of zinc sulphate.
Design Field experiments using a shower and a plunge dip complemented by in-vitro wettability experiments.
Procedure A flock of infested sheep was divided into groups and treated in a shower dip with clear or cloudy dam water plus up to 1.5% zinc sulphate. Another infested line of sheep was treated using a plunge dip with nil or 1% zinc sulphate. In both experiments, wetting was assessed after dipping and louse counts were conducted for 9 months after treatment. Five in-vitro experiments compared the wettability of dip wash containing diazinon with up to 1.5% zinc sulphate added.
Results In the shower dipping experiment, live lice were found at 1 month after dipping in the cloudy water groups with 0.75%, 1.0% and 1.5% zinc sulphate and at 2 months in the 0.75% zinc sulphate group. No lice were found at subsequent inspections or at any time in the groups that were plunge dipped. Zinc sulphate decreased the amount of dip wash retained by wool staples in all in-vitro experiments (P < 0.05).
Conclusion Zinc sulphate should be considered as a risk factor that could cause failure to eradicate a lice infestation. The risk can be overcome by ensuring that all sheep are saturated at dipping and that the dip wash, and any holding tanks, are agitated throughout the dipping event.