Vet's vision with Phil Rennie Tauranga Vets

With the end of the ‘zinc season’ close at hand, it is important to check your herd’s copper reserves. Zinc competes with copper for absorption at the gut level, which may lead to very low copper levels in May when zinc supplementation finishes. Variation in supplementary feed offered further complicates the situation.

Many farms adopt quite different supplement feed plans to ensure stock are fed adequately. For instance, in recent years large amounts of palm kernel in the diet have tended to lead to high copper levels in some herds. However, this is not always the case – especially when the level of palm kernel fed is fit for daily maintenance energy requirements, as opposed to being an additional energy source for weight gain.

To optimise productivity cattle should have some trace element testing done pre-calving. Liver biopsies provide the most accurate information, as it is a direct measure of the amount of copper stored in the liver. Samples from five-six cows are usually sufficient to give an indication of the herd copper levels. Alternatively, blood tests can be taken from eight-10 animals, providing a ‘snapshot’ of copper levels in the blood on the day of sampling.

Deficient animals can be easily identified this way, however the results do not provide any information on the amount of copper stored in the liver – so herds close to deficiency may appear normal on blood tests, and hence the need for increased copper supplementation will not be detectable. Remember the young stock too, as these animals have high copper requirements for growth and development.