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SHEEP HEALTH - COPPER POISONING

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THINK TANK ON CHRONIC COPPER POISONING

By Dr Neville Suttle, Moredun Foundation for Animal Health & Welfare,
Pentland Science Park, Bush Lane, Penicuik, Scotland EH26 0PZ

Eight years have passed since I contributed an article on "Chronic Copper Poisoning (CCP) in sheep" to Sheep Dairy News (Suttle 1990). In the years that followed there has been a rapid decline in the number of reported cases (Figure 1) and it was tempting to conclude that this and concurrent attempts to educate sheep farmers of the need to take preventive measures were bearing fruit. In recent years, however, there has been an equally dramatic upturn in cases of CCP despite another publication on the problem (Suttle 1995). Is the message being forgotten or is the upsurge a reflection of an increased risk in a situation that has always been delicately balanced? Is there new information which might help to shift the equilibrium in the dairy sheep farmer‘s favour?

A MODEL FOR THE DISEASE

Rather than restate the essential clinical, histological and biochemical features of CCP (Suttle 1990; 1995), I will present a model for the disease which illustrates the key role of the flow of copper into and out of the liver, the sheep‘s only storage organ. Imagine if you can the storage tank in your loft as the liver, the supply to it as copper being absorbed from the diet and the pipes leading from it as sources of loss or utilisation of stored copper (biliary and milk secretion, for example Figure 2). Figure 2 Normally a ball valve carefully balances supply and demand, but if the ball valve begins to leak, sooner or later there is an overflow problem. Sheep have a poorly developed mechanism for controlling copper inflow by absorption. If you tip a bucket of water into the tank to check the valve, you hasten the onset of the problem. Any unnecessary copper input during the year will hasten a CCP problem. CCP arises when the liver can neither store more copper nor hold what it has. The breakpoint is as hard to predict as a fault in the ball valve, but the consequences are more dramatic. Before the overflowing copper can be cleared from the body, it breaks down the blood cells which then clog up the vital organs, notably the kidneys. To continue the analogy, its like having the overflow pipe discharging into the house near the fuse board!

A CONCERN FOR THE DAIRYMAN

The dairy sheep farmer has particular reason to look to his plumbing! Only the Pedigree breeder offers his sheep such a plentiful supply of readily absorbed copper in the form of home-mixed or purchased concentrates. Copper concentrations are usually in the range of 12-25 mg/kg DM. That‘s twice as much as the average pasture or forage sample and, what is more, that copper will be roughly twice as absorbable as that from roughages. One reason for the upturn in the cases of CCP (Figure 1) may be the recent succession of dry summers which have necessitated drought-feeding, i.e. the partial substitution of grain for grass. Figure 1

SOME DO‘S

There are a number of small steps which every sheep farmer should take. While each on its own may not reduce the risk of CCP, together they may well prevent trouble for the vulnerable minority of the flock. Each step aims to reduce the level in the "tank" by reducing the starting level or inflow of copper.
  1. DO ask your feed supplier if he regularly checks the copper content of his products and ask for some results.
  2. DO ask your feed supplier if he regularly adds copper antagonists such as sulphur (S), molybdenum (Mo), iron (Fe) and zinc (Zn) to his products. Some of the smaller manufacturers have yet to adopt this practice.
  3. DO add antagonists to any home-mixed concentrate: S and Fe are the safest to introduce. The former can be added as gypsum (CaSO4) at 15 kg/tonne, replacing any limestone used. The latter can be added as ferrous sulphate at 1.4 kg/tonne and may help the gypsum to act.
  4. DO use loose mixes and whole grain wherever possible for routine or emergency supplementation. All grains are low in copper and consumption of whole grain keeps the rumen pH up and rumen protozoa "comfortable". These organisms are protective in that they generate sulphide which locks up copper as an insoluble and unabsorbable sulphide. Protozoa are needed to assist all the antagonists except Zn to do their stuff.
  5. DO ask for the "copper history" of bought-in stock: blood enzyme tests for liver damage are a worthwhile precaution for valuable sires or stock imported from another country.

SOME DON‘TS

There are a number of things that a dairy sheep farmer should never do if he or she wishes to minimise CCP problems and they complement the list of DO‘S
  1. DON‘T use in-feed medications to control pathogens such as toxoplasma or coccidia. The monensin which kills toxoplasma also kills rumen protozoa and increases risk of CCP. Use a toxoplasma vaccine for this purpose. Although there is no published evidence that coccidiostats harm protozoa, there is a strong possibility that they will, and their prolonged use is contraindicated for dairy sheep.
  2. DON‘T use concentrates or mineral mixes intended for cattle or pigs, they are usually supplemented with copper.
  3. DON‘T dose dairy sheep with either specific copper supplements (e.g. copper needles) or multi-element products which contain copper. ALWAYS check the label.
  4. DON‘T believe salesmen who try to tell you that their copper-containing supplement is "safe" because the copper is "chelated": safety and efficacy cannot go together and such products represent another unnecessary "bucket" emptied into the brimming "tank" of copper in the liver.
  5. DON‘T retain ram or ewe lambs for breeding purposes that come from sires or ewes which have produced offspring which succumbed to CCP. Vulnerability to the disease is under genetic control and even the slightest selection pressure may eventually reduce the number of fatalities.
  6. DON‘T apply multiple drug treatments at times of high metabolic stress (late pregnancy/early lactation): most treatments require the liver to do more at a busy time and may precipitate an overflow of copper leading to the haemolytic crisis.

PASTURE AND FORAGE TREATMENTS

The above precautions deal mostly with sheep or the concentrate component of the diet. There is scope for manipulating forage resources so that they provide less absorbable copper. The liming of pasture is likely to increase the concentration of molybdenum in the herbage, thus increasing the opportunity for "endogenous antagonism". Where mixed stocking or mixed sheep enterprises are present, priority for recently limed pastures should be given to the dairy sheep flock. Where the available Mo level in the soil is low for geochemical reasons, it can be topped up by fertilising strips with sodium molybdate at around 0.3 kg/hectare. With a little ingenuity sodium molybdate could also be added in solution to conserved forage before or after harvesting at 7.6g/tonne. Alternatively, spray application of the solution containing 0.19g/litre of sodium molybdate to baled hay at feeding time at a rate of 1 litre per 25kg bale will add 3mg Mo/kg hay. There is usually sufficient sulphur in good quality forage to begin to potentiate the Mo-antagonism. The dusting of gypsum on to forage works better for silage than hay, the rate being 15kg/tonne again.

CONCLUSION

The perceptive reader will note that the address from which this article comes has changed completely since the last one written. The Moredun Institute and Foundation are in the process of re-uniting on a green-field site with splendid new research facilities. It will, however, require increasing support from the livestock industry to continue to provide new insights into the old diseases like CCP which continue to plague sheep farmers yet be ignored by policy makers. It will also require good advice to be heeded if we are to consign CCP to where it belongs - the history book.

REFERENCES

Suttle, N.F. (1990) Chronic copper poisoning in sheep. "Sheep Dairy News" Journal of the British Sheep Dairying Association 7, 10.

Suttle, N.F. (1995) Copper poisoning in ruminants. Newsletter, Volume 2, No.7. Moredun Foundation.

(From Sheep Dairy News Vol 15, No.1).

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