“The only way to reach a definitive answer to this question is to perform liver (fixed tissue) or blood tests. The bolus packaging cautions against providing other mineral sources, but I test multiple livers annually & my flock does better with a loose mineral available. I use Redmond 90 Selenium Salt, but since adding boluses years ago- my flock’s loose mineral consumption plummeted. We feed less than half of what we used to. It’s my assumption that the boluses provide a solid baseline for most of the sheep with only certain individuals having higher mineral needs. The boluses solve the variable consumption problem for most of the flock, but loose minerals are a safety net for the few who still need it.."