Changing proiten in feed

Question
We have a 9 year old QH mare due the first of march. The last time she foaled we used a expensive feed. We have since found a feed made locally that is very reasonable in price. But he will only make 12% feed. What and how much can I add to the feed to bring it to 16% protien and not have to give her alot more feed? She is a easy keeper. We also feed very good quality grass hay. Can we use something like calf-manna??

Thank you,

Bill

Answer
Hi Bill,
Thank you for your question.  I've done exactly the same thing in the past, in attempt to feed many different groups of horses without keeping a lot of different feeds on hand.
It is best to use a manufactured protein supplement to add to your 12% instead as a protein byproduct like soybean meal or corn gluten meal.  Although they would work, they are not mineral enriched and would have an inverted Ca:P ratio...leaving your broodmare deficient in mineral.
Calf-Manna would work at a ratio of 70% of your 12% feed and 30% Calf-Manna.  The Ca:P ratio is lower than I'd like to see but may work out in the end of your hay has a higher ratio.  The amount that you need to feed daily depends on the quality of your hay and the mare's stage of gestation.
A few other ideas would be the Triple Crown 30% supplement or Purina's 'Nature's Essentials Enrich 32 Supplement'...either one at 12% of the mix and your 12% feed at 88% of the mix.  
That should provide you with a starting point.  If you have your hay analyzed by your local feed dealer, I could calculate some feeding rates for you.
Thanks, Corlena