24 July 2002

Extra trace element warning

THERE is no evidence that feeding excess amounts of certain trace elements will enhance dairy cow performance, according to one researcher.

There have been claims that increasing supply of some trace elements above current recommendations will improve cow healthand performance, says ADAS researcher Caroline Rymer. "Most of these claims are related to chromium, copper, iodine, manganese, selenium and zinc."

These benefits were examined in an MDC-funded review. "Supplementing extra zinc seemed to help improve cow fertility, disease resistance and health status. But there was no evidence on how much excess zinc should be fed, with some studies showing no benefit at all.

"Similarly, some studies have shown that feeding selenium above recommended requirements is beneficial to cow health. However, vitamin E status and other dietary factors affect the response, if any."

The review also aimed to develop a decision support, helping producers to assess and tackle trace element nutrition for dairy cows. However, it was not possible to predict benefits with any confidence and there is a risk of toxicity over time with excess copper, selenium and iodine, explains Dr Rymer.

Instead, she advises checking the mineral content of feed and forages where a deficiency is suspected. Also, consider whether antagonistic minerals are in excess, reducing availability of the deficient mineral.

She warns producers using che-lated minerals to be cautious when changing products as they can vary in their availability to stock. &#42