I use the TC 30% AND supplement minerals as it’s still not enough to balance the hay…
My yearling is 15.1, around 900 lbs. She is also 50% TB like your filly.
I am NOT a big fan of ration balancers. I do feed some alfalfa. Timothy is best with a little alfalfa added. Alfalfa pellets or cubes are NOT the same as good alfalfa hay either. Interesting that many feel alfalfa is “bad” as it is the first ingredient in Triple Crown Growth. However, with Physitis I would go with Timothy hay, some oats and water, until you get the problem resolved. Then go with a growth formula feed that is recommended for yearlings.
At one time you mentioned feeding BOSS, I read that for some horses, which tend toward being “fat”, BOSS should not be used.
Good Luck I hope that your filly resolves quickly.
Hope this is helpful, from: http://www.understanding-horse-nutrition.com/developmental-orthopedic-disease.html
Physitis
Physitis is nothing more than swelling around the growth plate of a bone. It usually occurs in the bones of the legs, and usually in bones that are closer to the ground.
There are a few theories about why physitis occurs, including malnutrition, faulty hoof growth, and compression of the growth plate. Compression of the growth plate seems to be the most likely cause, as physitis is most often seen in foals that are large for their age, grow quickly, and are top-heavy. It is most often seen in the summer when the ground is hard and dry. It is also seen a lot when the calcium:phosphorus ratio is unbalanced.
Treatment includes reducing feed intake to reduce weight and/or growth rate. The diet also needs to be evaluated to ensure that the calcium:phosphorus ratio is correct (for treatment purposes it should be around 1.6:1) and the amount of protein is not excessive. Confining exercise to small areas where the footing is soft is also part of treatment, as is ensuring that the feet are trimmed correctly and often.
I’m curious why you think ration balancers aren’t a good idea, but feel minerals can be properly fed with just hay and oats 
Physitis is indeed inflammation, but it’s MAIN cause is unbalanced minerals, and unless you have just fantastic hay, hay and oats don’t usually cut it.
I’m another who would be hestitant to just feed hay and oats to a youngster. Oats are deficient in Calcium, one of the essential minerals that youngstock need. Feeding just straight oats can precipitate physitis, not cure it.
^^^^^THIS^^^^^
Turn out for sure!
Protein is not the problem! 
Minerals are usually the problem - usually the wrong balance, either too much calcium, or not enough phosphorous, or something like that.
Here is a really good article on it! :yes:
http://pacificcoastjournal.com/index.php?option=com_content&view=article&id=60:focus-on-physitis&catid=48:misc&Itemid=55
Exactly
Though excesses of protein have often been blamed for high incidences of DOD, the more likely culprit appears to be excesses of digestible energy (DE).
If you’re feeding 8lb of a 16% “foal” feed, you’re probably feeding too many calories, and that, the DE is the problem, not the protein.
Extra protein is, to a point, just wasted money, expensive pee. But to say “lower the protein” can too easily lead to cutting it back TOO much and depriving a growing youngster of the protein he needs to develop properly.
[QUOTE=JB;6443797]
Exactly
If you’re feeding 8lb of a 16% “foal” feed, you’re probably feeding too many calories, and that, the DE is the problem, not the protein.
Extra protein is, to a point, just wasted money, expensive pee. But to say “lower the protein” can too easily lead to cutting it back TOO much and depriving a growing youngster of the protein he needs to develop properly.[/QUOTE]
Exactly!! JB is right.
Kentucky Equine Research have taught me enormous things about these balances and also taught me the basic calculations. It made me dizzy at first, but like anything, once you get it, it’s easier. So here they are for anyone who is interested.
- If you balance the calcium and phosphorous, adequate copper absorption will follow suit.
NOTE: Whoever said oats are high in calcium are wrong. They are very high in phosphorous which makes them a good balance for grass-alfalfa mixed hay. It doesn’t take much oats to balance this type of hay.
- Per 1 pound, grass hays and pasture grasses are 0.5 grams of calcium and 1 gram of phosphorous, approximately 8-10% protein, depending on type and cut. This is inverted. You always wants calcium to be higher than phosphorous.
- 1 pound of alfalfa is 5.64 grams of calcium and .999 grams of phosphorous per pound, plus 16-18% protein.
- 1 pound Timothy is 1.954 grams of calcium to 0.91 grams of phosphorous and approximately 8-11% protein, depending on cut.
- 1 pound of oats is 2.27 grams of calcium and 15.43 grams of phosphorous.
- 1 pound dry beet pulp is 2.81 grams of calcium, 0.41 grams phosphorous.
Note: The powers that be decided that even in America, calculations are metric. So, some conversions for you:
11.0% protein means that every kilogram contains 110 grams of protein. (1 kilogram = 2.2 pounds). 16-18% = 160-180 grams.
You can use those measurements to figure out what your particular diet regimen is providing, your bags of kibble should provide you similar notes. Using those guides, you know whether what you’re feeding is right, especially whether you even need foal kibble, or just a bit of oats with a multimineral/vitamin. It really depends on whether your youngster is feeding on grass pasture or all grass orchard/bermuda/coastal hay, or whether you incorporate some alfalfa to the diet.
Timothy hay is the caveat - it is balanced calcium to phosphorous.
For example diet for an easy-keeping solid-working adult horse weighing about 450-500 kg (990 - 1100 pounds): If 12.5 pounds of timothy hay are fed (27.5 kilograms) you have a total of 24.4 grams of calcium and 11.3 grams of phosphorous, but still only 8-11% of the diet containing protein. Add 1 pound of alfalfa (2.2 kilograms) and you add 5.6 grams of calcium, 0.999 grams of phosphorous and 16-18% of protein. 1/2 pound of oats (1.1 kg) is 1.14 grams of calcium, 7.7 grams of phosphorous.
A total calculation of this feed is:
31.14 grams of calcium
19.999 grams of phosphorous
2360 grams of protein or 13.1-14.75% protein or 131-147.5 grams/10 kg.
This is enough protein for an 450-500 kg adult in solid-work. The calcium to phosphorous ratio of 1.5 : 1 which is a healthy ratio. (divide total calcium by the phosphorous).
According to KER, actively growing horses needed:
30 grams of calcium per day.
21 grams of phosphorous
16-18% protein, so 160-180 grams/10 kilogram of weight. Too much protein just gets excreted by the horse.
Timothy or other grass hay doesn’t have nearly required enough protein, so protein needs to be supplement. Timothy hay, however, is correctly balanced calcium to phosphorous, approximately 1.5 to 2.1 : 1 depending on cut.
You can add a no-calorie balancer to ensure enough magnesium (minimum 5 grams in growing horses), copper, vitamin A, E, manganese, etc. are in the diet.
If you’re feeding a foal kibble, read the label. Some foal kibbles will tell you that their product is ideal for youngsters on an all grass or pasture diet. Others will state their kibble balances youngsters fed a grass/alfalfa mixed diet.
A 16% protein foal kibble with 12% calcium and 8% or less phosphorous is best suited for a grass pasture, grass hay diet because it’s enough protein and should supplement the calcium.
Pasture grass and all non-timothy grass hays are 0.5 calcium to 1.1 phosphorous, therefore, they are slightly inverted. Therefore, you want lower phosphorous in your kibble.
Timothy hay is the exception to the rule: It is balanced 1.5-2 calcium to 1 of phosphorous, but only 8-11% protein, so it would still be fine to feed foal kibble that has 12% calcium to 8% phosphorous kibble plus the extra protein the kibble provides.
If you want to feed mixed grasses/alfalfa, mostly grass hay, then you could lose the kibble, add only a small ration of oats, but add a no-calorie multi-mineral/vitamin as long as the % of calcium is about 12% to at least 8% phosphorous.
Alfalfa provides lysine - needed for growing bodies. Grass/timothy does not provide this, so make sure your kibble does.
So, there’s the facts I’ve been provided by KER and now anyone and everyone should be able to figure out their balances for youngsters.
They provided me tables for month 9, 10 and 11 pregnancy plus lactation for the mares too for calcium/phosphorous protein. PM me anyone who wants that.
Just a caveat on balancing the calcium and phos and having copper follow suit:
Iron concentrations directly affect copper (and zinc), so if the forage is high in iron, which came from high Fe in the soil, then not only will the forage bs low in Cu, the horse will have even lower uptake, no matter how much or balanced the Ca and Phos are 
[QUOTE=JB;6443661]
I’m curious why you think ration balancers aren’t a good idea, but feel minerals can be properly fed with just hay and oats
Physitis is indeed inflammation, but it’s MAIN cause is unbalanced minerals, and unless you have just fantastic hay, hay and oats don’t usually cut it.[/QUOTE]
Being overweight can also be a contributing factor of physitis …my 9 month old gelding was over weight had a balanced diet my vet advised he loose some weight…once that happened his joints returned to normal…all I did was cut back.
Dalemma
Sure - excess DE/calories is absolutely a factor in physitis.
[QUOTE=Dalemma;6445248]
Being overweight can also be a contributing factor of physitis …my 9 month old gelding was over weight had a balanced diet my vet advised he loose some weight…once that happened his joints returned to normal…all I did was cut back.
Dalemma[/QUOTE]
I eagerly await the day when horse folk at large realize and accept that “hunter fat” is crippling at best and deadly at its worst. Babies are not the only ones encountering health ans physical problems as a result of over feeding.
Why we (as a group) think that fatfatfat horses are beautiful when we know full well the consequences of excess fat and weight for any species is far beyond me. We seem to equate “market hog fat” with great husbandry in many disciplines.
Amen Jackie 
The swelling in her front legs is gone and the back legs are much improved so I think we are on the right track. She looks good!
Yay!!
Woohoo!! 
Woot! Woot!
[QUOTE=JB;6443661]
Physitis is indeed inflammation, but it’s MAIN cause is unbalanced minerals, and unless you have just fantastic hay, hay and oats don’t usually cut it.[/QUOTE]
No disrespect but I don’t think this can be stated as fact.
I have been in the TB horse business for many years, 20 of those in Lexington KY. I have raised quite a few and have friends that manage some of the best TB farms in the world.
Not one of them would give a definitive cause for physitis. Though they would agree with a number of the suggestions offered in this thread. But I would bet my bottom dollar none would site the “MAIN cause is unbalanced minerals”. Why? Because these farms have access to the some of the best staffing, nutritionist, 'hay, oats and water" etc… So I can promise you everything is looked at and analyzed. Yet there will always be some in every crop that will suffer to one degree or another from physitis. NOTHING is overlooked. These are very expensively bred TBs owned by wealthy people who do not grip about their board bills. I also have friends that are not in a position to go to such lengths with their own or boarders. We can’t. But I know my feed and my hay. Most years we rarely have to deal with physitis in any of our youngsters. My point is there will always be the “odd” one or two depending on the population. However if a breeder has a higher percentage of physitis then the accepted norm this is cause for concern. ALL things should be reviewed, care, feeding, management, environment, etc…
When I have been asked to take a look at my hobby breeder friends youngsters, who only have a couple at best I would say the biggest problem IMO is too much “lovin”.
Can mineral imbalance play a significant roll, yes but rarely. Is it the main reason, IMO absolutely not. Unless of course the person raising the horse doesn’t have a clue.
This is just my opinion but it is based on experience and working with and or taking advise from some of the best in the world at what they do.
I have been breeding for 16 years and this was my first case of physitis and I have had exactly zero OCDs so I feel like I have a pretty good handle on my nutrition. This is my first non 100% TB though and also the first I fed for the show ring so I am sure both those things contributed. Thankfully we seem to be on the right road right now.
