Control of Copper (Cu) Poisoning in Sheep

Phil Rogers MRCVS <philrogers@eircom.net>
Grange Research Centre, Dunsany, Co. Meath, Ireland
21-Mar-2001

COPPER POISONING

All breeds of sheep can be poisoned by ingestion or injection of excessive amounts of Cu. However, some breeds and their crosses are very susceptible to Cu poisoning. These include Island breeds (Texel, Ronaldsay, Soay etc) and some continental breeds (Charolais, Rouge). Cu poisoning has occurred in sheep on pasture which had been fertilised with high-Cu pig slurry. In very rare instances, Texel sheep have been poisoned at pasture with as little as 14 mg Cu/kg DM, and no other known source of Cu intake.

Sheep should get no Cu supplement in a drench, mineral mix, lick etc unless a veterinary surgeon has diagnosed Cu deficiency in the flock by blood test and/or on clinical/postmortem findings. Even then, it is safer to give Cu supplements to sheep only as directed by a veterinary surgeon (see 3, below).

Under current EU Legislation, complete sheep feeds must contain no more than 15 mg Cu/kg in total feed (17 mg Cu/kg total feed DM). Assuming a maximum DM intake of 2 kg/ewe/d, the EU permits a maximum oral intake of about 34 mg Cu/ewe/d (less, pro-rata, for lighter sheep). To be safe (in the case of susceptible breeds), stay below the maximum permitted by the EU.

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REMEDIAL ACTIONS DURING AN OUTBREAK OF Cu POISONING

Consider immediate implementation of the following actions if postmortem examination confirms a diagnosis of Cu toxicity in sheep and/or feed analysis confirms levels >17 mg Cu/kg total dietary DM (including sheep licks, supplements, drenches etc) and/or analysis of blood or liver samples suggests exposure to excessive Cu:

a. IDENTIFY AND REMOVE THE SOURCE OF HIGH Cu (cattle rations or minerals; high-Cu mineral mixes, licks, drenches, corroding Cu water pipes, Cu-contaminated pasture etc).

b. ADD Cu-ANTAGONISTS TO THE DIET of the "at-risk groups" for 4-6 weeks. The best researched antagonists are Mo, S, Zn and Fe.

On a veterinary prescription, a specialist mineral supplier can prepare a mixture of Cu-antagonists as follows:

Cu antagonist

Weight (kg)

Weight of antagonistic element

Sodium sulphate (23.2% S )

10.7759

2.5 kg S

Ferrous sulphate (20.1% Fe)

0.4975

100 g Fe

Zinc sulphate (22.7% Zn)

0.2203

50 g Zn

Sodium molybdate (39.5% Mo)

0.0177

7 g Mo

TOTAL WEIGHT

11.5114

(sum of the above)

 

Have this amount mixed professionally in 500 kg of concentrate feed.

Label the feed: Special Copper-antagonist feed, containing an additional 5 kg S, 200 g Fe, 100 g Zn and 14 g Mo per tonne (equivalent to an addition of 0.5% S, 200 ppm Fe, 100 ppm Zn, 14 ppm Mo). Use only as advised by your vet. (Guidelines are below, but need to be adapted for the individual situations by the advising vet).

Sheep on ad libitum concentrate feed: Mix this feed 50/50 with a low-Cu sheep concentrate and feed the mixture ad libitum.

Ewes or adult sheep whose concentrate DM intake is c. 50% of total DM intake: Feed up to 1 kg of this feed/head/d (to provide up to 50% of total DM intake).

b4. WARNINGS: Feed only to sheep at risk of Cu poisoning. Feed for 4-6 weeks, only as directed above, and only under veterinary supervision. The purpose of this feed is to remove Cu from sheep at risk of Cu poisoning. It does not guarantee to save clinical cases, nor to totally prevent new cases.

SIDE EFFECTS: If scouring or severe side effects occur in sheep on this feed, withdraw the feed and seek veterinary advice immediately. One solution may be to alternate the feed every second week with a low-Cu sheep feed, or reduce the daily allowance of this feed to half, substituting with other feed. If fed to excess, or for long periods, Mo toxicity and/or Cu deficiency can occur.

PREVENTION OF Cu TOXICITY

1. Ensure OPTIMAL TOTAL ORAL Cu INTAKE by sheep (8-15 mg Cu/kg feed DM).

  • a. High Cu levels (21-40+ mg/kg DM) occur in byproducts from Cu vats used in the brewing/distilling/refining sector (barley distillers grains, beetpulp, corn distillers grains, molasses etc), some high-protein feeds (beans, corn gluten, cotton seed, groundnut, linseed, palm kernel, safflower, sunflower, soya bean etc) and in potatoes which have been sprayed with "bluestone" (Cu sulphate).

    Farmers should ask suppliers to CERTIFY the Cu content of "straights" before including them at high level in farm-mixed sheep feeds.

    b. Apply high-Cu PIG SLURRY to bare pasture only. If there is good grass cover at the time of slurry-application, slurry can contaminate the leaf surface directly, causing cause high levels of Cu in the grass. Pig slurry can be applied safely to bare pasture. In that case, no leaf-contamination occurs and uptake of Cu from the soil (via the grass roots) is negligible.

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    2. DO NOT FEED CATTLE RATIONS/CATTLE MINERALS TO SHEEP

  • a. Some Coarse Feeds for calves and most standard dairy rations contain 40-80 mg Cu/kg. Special dairy Summer Feed, to be fed at 1 kg/cow/d, may contain up to 450 mg Cu/kg. As little as 1 kg of calf feed or dairy ration/d, or 100 g dairy Summer Feed/d could supply enough Cu to poison sheep after a few weeks.
    •
  • b. Cattle minerals and blocks can contain 1500-5000 mg Cu/kg. At the low level (1500 mg/kg), 23 g of such mineral/d would supply enough Cu to exceed the total daily input for sheep permitted by the EU. At the high level (5000 mg/kg), as little as 7 g of cattle mineral/d would supply enough Cu to exceed the total daily input for sheep permitted by the EU. Such inputs could supply enough Cu to poison sheep after a few weeks.
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    3. SLOW RELEASE ORAL Cu IS SAFEST FOR SHEEP

    If sheep need a Cu supplement, oral Cu oxide capsules or Cu-containing glass boluses are safer than feeding, or drenching, or injecting Cu compounds. For example, CuO particles in a gelatin capsule can be given at doses of 4 g (ewes), 2 g (store lambs) or 1 g (lambs 1-2 months of age). Dose once or twice/year, as needed.