In early January this year a local dairy farm discovered through routine bloods and liver biopsies that the copper and selenium levels in the herd were getting quite high. This farm is a high producing, high input herd.
The minerals are given daily in the feed and the mineral is a high quality chelated formulation (much more readily absorbed than the sulphate or selenate forms). The herd had not shown any symptoms of selenium or copper toxicity but it was decided to stop the mineral supplementation for a period of time to reduce the chance of toxicity occurring (particularly for copper - as we have seen cases of copper toxicity in herds with levels similar to those found in this case). After 6 weeks without the minerals going in (apart from Zn for FE prevention) the animals were retested to see how the levels had changed. The results were quite surprising:
The liver copper levels dropped by an average of 1100 units and the liver selenium levels dropped by an average of 7700 units!! They still remained in the adequate range and even still a bit high for a couple of the copper levels. But the risk of toxicity was reduced. The farmer has resumed the minerals now at 80% of what they were being given previously (4g instead of 5g/cow/day). The herd will be tested again in a few months time to check that this level is adequate. The benefit of checking levels in this case was to reduce risk of toxicity and to save some cost by reducing the mineral rate per cow per day. Not many farms would suddenly stop giving minerals mid season, but there can be drastic changes in the way animals are supplemented for example through the dry period. During this time levels could drop substantially (especially with foetal demands) if animals were not supplemented. Checking regularly with blood and liver sampling can be very useful to ensure all is on track.