In a recent article by J. Gill and F. Hill, palm kernel extract (PKE) as a feed supplement was discussed, in particular, with reference to its feed characteristics. The product is imported from Asian and Pacific countries and costs about 28c/kg DM which makes it a reasonably cheap feed when compared to other supplements such as hay or silage. It has a ME of around 11 MJ/Kg DM, however lacks in palatability, and has a mineral content that it is high in copper and selenium, but low in magnesium.
To date, in New Zealand, there have been two cases of copper toxicity resulting in the death of several cows which were being fed PKE. In both cases the cows were being fed PKE as well as zinc for facial eczema protection with one lot of deaths occurring after the cows were transported.
Copper is taken up from the diet and stored in the liver. Toxicity can occur suddenly from a massive intake/overdose of copper, or as a result of excess intake over a prolonged period. In chronic copper poisoning the copper builds up in the liver and can be suddenly released into the blood during a stressful period (eg transport, deteriorating plane of nutrition, pregnancy), or as a result of extra copper supplementation. Acute copper toxicity usually occurs as a result of over supplementation of copper. The excess copper in circulation damages red blood cells and can cause sudden death.
Selenium toxicity can occur as a result of prolonged periods of exposure or, acutely, from ingestion or injection of high doses of selenium. Chronic exposure to toxic selenium levels causes weight loss, rough coats, deformed hooves and poor repro performance. Acute selenium poisoning causes gut upsets with diarrhoea, breathing difficulties, unsteady gait and death within a few hours of the injection, or ingestion of, the toxic dose.
The aim of this write-up therefore is to make farmers aware of the mineral content of PKE so that precautions can be taken when it comes to supplementing cattle with the trace elements present in PKE.
Some take home pointers then include:
· Measuring the copper and selenium status, via liver biopsies and blood tests respectively, during the PKE feeding period to assess its effects on trace element levels.
· Extra selenium or copper supplementation should be avoided while animals are being fed PKE unless testing shows otherwise. Ideally the PKE would be mixed with grain making it more palatable, adding more protein and energy to the diet, and diluting out the high trace element component of the feed.
· PKE should not be fed to sheep (or young calves), as they are more susceptible to copper toxicity than adult cattle.
· Farmers should also be aware that copper and selenium toxicity does not only cause sudden death. Other effects on animal condition and production will also be occurring.
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