QUESTION: I bought some mineral salts to feed the deer on my property. It's made for cattle. On the bag it says not to feed it to lactating cows. Is this a bad choice to feed to my does? I don`t want to hurt the fawns. - Clair
ANSWER: Without knowing the specific contents of your “salts” it's very difficult to answer your question. However, I'll take a stab at it.
Some packaging for products containing rumensin once carried labels cautioning: “Do not feed to lactating dairy cows.” Rumensin blocks contain an active ingredient called monensin, a proton ionopohore that enhances digestion and helps control rumen bacteria in ruminants like cows, goats, sheep and deer. The caution against feeding it to lactating dairy cows was not related to calf health. It was due to the potential for being absorbed into milk that is sold for human consumption. That all became moot when the FDA approved monensin in total mixed ration systems in 2004, and in component feeding systems in 2005.
If your product contains Rumensin or monensin, that is likely the reason for the labeling. It shouldn't harm free-range fawns and if consumed in enough quantity, could increase milk production efficiency in lactating does. However, as you have far less control over food and mineral intake by free-ranging deer, any such effects would likely be minimal.
The same logic that applies to food plot seed blends also applies to mineral blocks and powders. You're better off using products that are specifically designed for deer, not for domestic livestock. They will work better for deer and you won't be paying extra for products or materials that you don't need.
Incidentally, sodium and chloride, the components of salt, aid in regulation of fluid volume and blood pressure; maintenance of osmotic balances and buffer systems and conduction of nerve impulses. The need for sodium and chloride increases in lactating females and because they are not readily available in the plants deer consume, putting salt out during the nursing season can be beneficial.