Ranitidine 900 mg. x 3 for 2 years now I believe.

That's a low dose.  Should be 6.6 mg/kg so for 500 lb would be 227.2 x 6.6 = 1500 mg x 3.  Even at that dose the effect on gastric ulcers is less than when using omeprazole so it is questionable how much this is actually doing.

Effects of treatment with omeprazole or ranitidine on gastric squamous ulceration in racing Thoroughbreds.

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I know H2 blockers can cause mineral malabsorption in humans so assume
it will in equines too.

That's not a safe assumption since horses have some very significant differences from humans in how they absorb minerals.  In any case, reductions have only been demonstrated for calcium and magnesium and those are very small amounts:

http://www.amjmed.com/article/S0002-9343%2808%2900787-0/abstract

There are many, many other studies on this.

Plus, these effects are seen with the proton pump inhibitors, NOT H2 blockers like ranitidine:

Proton-Pump Inhibitors and Hypomagnesemic Hypoparathyroidism — NEJM

 

There are no cases of iron deficiency/iron deficiency anemia related to acid suppression.  I'm sure if that was happening it would have been noticed by now.

There has never been a reported case of iron deficiency in an adult horse, even with blood loss.  Since the average horse has at least 10 times  more stored iron than needed to prevent anemia (and IR horses much more), that's not too surprising.

 Eleanor in PA
www.drkellon.com
EC Co-owner
Feb 2001