Determination of serum/plasma vitamin A and E testing at the AHL

Felipe Reggeti, Nick Schrier, Tracy Van Raaij

Animal Health Laboratory, University of Guelph, Guelph, ON

AHL Newsletter 2023;27(3):5.

Vitamin A is an essential nutrient that is necessary for dim-light vision, normal bone growth and maintenance of epithelial cells, and is not produced by ruminal bacteria.  Clinical signs of deficiencies result from impairment of these functions, but the most critical economical impact is related to the effects on reproductive function.  Pro-vitamin A carotenoids are abundant in green plants/grasses, and are converted to active retinol in the intestinal epithelium and liver.  Deficiency may occur when animals are fed hay/straw without vitamin A supplementation (e.g., winter months), as carotenes progressively deteriorate upon storage, as well as in association with conditions causing malabsorption.  Clinical signs of vitamin A deficiency may include:

• night blindness and papilledema (usually the first clinical signed noted);
• bone growth defects;
• poor maintenance of epithelial cells resulting in squamous metaplasia of glandular epithelium, reduced thyroxin secretion, xerophthalmia, corneal keratinization;
• skin problems such as scaly skin, dry hair-coat, scaly hooves with vertical cracks;
• neurological signs such as syncope and convulsions caused by elevated CSF pressure due to impaired fluid absorption;
• reproductive problems such as infertility (reduced count of motile sperm cells), abortions and placental retention;
• congenital defects such as optic nerve damage, retinal dysplasia, malformation of cranial bones;
• impaired immune system;
• weight loss (may be due to overall poor nutrition).

Vitamin E is an essential antioxidant that helps maintain cell health by preventing lipid membrane peroxidation from continued exposure to free radicals, a process that works in conjunction with the action of the selenium-containing enzyme glutathione peroxidase.  Vitamin E is abundant in green forages, and similar to vitamin A, deficiency may occur when animals are fed poor quality hay or straw without vitamin E supplementation.  Conditions known to respond to vitamin E (and/or Se) supplementation include nutritional muscular dystrophy (multiple species), mulberry heart disease (pigs), reproductive inefficiency and decreased resistance to infections. 

Some of these health issues may be prevented by quantification of vitamin A and E concentrations in appropriate samples, and correcting suboptimal levels via supplementation.  Determination of plasma/serum concentrations is practical and commonly used to diagnose nutritional imbalances, although liver concentrations are better indicators of body reserves.  The AHL now offers quantification of the concentration of vitamins A and E in serum or plasma samples from multiple species by HPLC, and we are currently working on developing methods to assess concentrations in tissues.  The volume of serum/plasma required for testing is less than 1 ml.  For sample collection, we recommend separating the serum after clot formation (~1 hour), or centrifuging the blood to obtain the plasma soon after venipuncture.  Do not use tubes with gel separators and avoid hemolysis.  Transfer the sample to a transport tube, protect from light exposure, and ship refrigerated or frozen.

References

1.  Radostits OM, Gay CC, Hinchcliff KW, Contstable, PD.  Chapter 30 - Diseases associated with nutritional deficiencies. In: Veterinary Medicine: A textbook of the diseases of cattle, horses, sheep, pigs and goats, 10th ed. Radostits OM et al, eds. Elsevier, 2007:1771-1777.