The past few year we have sent in an annual liver sample from healthy animals that we harvested for home consumption. This enables us to see where we are with our mineral supplementation and adjust things as needed.
The past two years we gave copper oxide wire particles boluses to the ewes during pregnancy as our copper levels were at the low end of normal. This year we are close to the upper limit for normal so we will skip that this year.
We have been increasing the selenium in our mineral mix and we can see the results over time, obviously we are seriously deficient in our soils on the farm.
Katahdins appear to need more copper than some other sheep breeds but I feel much more confident supplementing it (if needed) when I have an idea of where the sheep are. Sheep do need copper, especially during pregnancy for normal lamb development, but copper toxicity can be induced if you supplement indiscriminately.
The test we use is run by Michigan State University and you do need to submit samples through your veterinarian. The test is $55 and we feel that it is money well spent. You only need a small piece of liver and it can be frozen.