Ok, ok... I was just getting tired of talking about biochemistry and how it relates to vitamin deficiencies in animals. So I'm skipping ahead!
But I cannot skip the biochemistry of Folate and Cobalamin deficiencies.
Click on the photo below to get some more information on the relationship between Folate and Cobalamin. Do you remember the Folate Trap?? That's a tough one.
Anyway, the active form in the body for Folate is Tetrahydrofolate (everyone in the TTC community knows what I'm talking about here).
In order to convert inactive folic acid/folate to active tetrahydrofolate you also need Vitamin B12 (cobalamin). That being said a Vitamin B12 deficiency can also present signs of a Folate deficiency.
I think most people know that a woman needs folic acid or folate supplementation to prevent neural tube defects during embryogenesis... a.k.a. early pregnancy. Neural tube closure occurs similarly in all mammalian species (as far as my limited knowledge goes - see here for more embryology information). Also see here for a more visual representation of neural tube formation in embryogenesis. In the pregnant woman model of folate deficiency we get improper closure of the neural tube and the resulting fetus can develop a condition called spina bifida.
Not all cases of neural tube defects are due to folate deficiency, but it is just well-known, so something to keep in mind for your list of differentials.
Folate Deficiency in Dogs and Cats
Since the last few Vitamin deficiency posts have been about poultry, I wanted to ensure I included some information on companion animals. The main one I wanted to discuss is malabsorptive forms of protein-losing enteropathies. If you have a condition that limits your absorption of nutrients from the small intestines, you can end up with a folate or cobalamin deficiency.
Patients with malabsorptive protein-losing enteropathies will present with a good appetite, the animal has chronic diarrhea (this may or may not be responsive to antibiotics like Metronidazole or Tylosin), or chronic intermittent diarrhea. Sometimes vomiting (I find more of this in cats with PLE).
If it is the first time seeing a patient, you may consider treating the symptoms, as the diagnostics are more invasive. You may decide to try a novel protein diet or anallergenic diet in cases of suspected food intolerances or inflammatory bowel disease, along with probiotics. When you go to perform your blood work, you can collect enough of a sample for your chemistry panel and CBC, which if you want to ensure you are not missing anything, you can add on a folate and cobalamin level to this (fewer pokes for your patients as long as your laboratory runs these tests). A TLI (trypsin-like immunoreactivity) test will rule out exocrine pancreatic insufficiency (EPI - I can tell you I have never found a positive, so it is not that common). The patient I would test for EPI would be a young, undernourished German Shepherd dog that is still eating a lot of calories, but not able to put on weight.
Ultimately, your diagnosis of what type of chronic enteropathy your patient has is an intestinal biopsy. Check with your pathology lab on what they need for your samples, some prefer full thickness intestinal biopsies and others can read endoscopically acquired samples. You job as the primary care veterinarian is to collect diagnostic samples.
Folate deficiency can show up in proximal small intestinal diseases, but I have seen more laboratory confirmed cases of Cobalamin deficiency, more commonly found in cats. A folate deficiency can also be a cause of an anemia.
Treatment for a folate deficiency is simple and more cost effective for a pet owner than the anesthesia for biopsies, so a supplement of folate (and cobalamin) may be in order prior to biopsy.