Vitamin A—an essential micronutrient
Vitamin A is a fat-soluble micronutrient found in a dog's body in the form of retinol and retinyl esters. It is essential for maintaining normal vision, immune system function, and reproductive function. It supports the health of the skin, epidermis, and mucous membranes. It also plays a role in cell differentiation, gene expression, and antioxidant processes. It is essential for maintaining the body's overall vitality. However, in a BARF diet, particular care must be taken to ensure that vitamin A levels are not too high because it accumulates in the liver.
In nutrition, the term vitamin A is used to refer to three compounds: retinol, retinal, and retinoic acid. It is a vitamin with a very broad range of effects and an enormous role in physiological processes, which is why particular attention is paid to its importance in veterinary medicine and animal nutrition. A highly bioavailable source of vitamin A is a very important component of a homemade diet.
Vitamin A metabolism
In carnivorous animals, various enzymes are required for vitamin A metabolic pathways. In the form of retinyl esters, it undergoes hydrolysis in the small intestine with the involvement of pancreatic lipases. This releases retinol. In dogs, vitamin A is absorbed mainly in the jejunum, from where it is transported to the liver together with lipid particles.
The liver contains so-called stellate cells in which vitamin A is stored and from which it can be released when needed.
Excess vitamin A—what causes it?
Vitamin A hypervitaminosis is often associated with combining its main dietary source, namely liver, with various vitamin A-rich supplements (cod liver oil, fish oil) and treats (e.g. dried liver). The problem is an excess that persists over an extended period, lasting weeks or months. There is no need to worry if an animal eats a large portion of liver on a single occasion; what matters here is the timescale and regular feeding. Particular care must be taken with dried liver. Drying involves substantial water loss, to the extent that 30-40 g of dried liver corresponds to 200-300 g of fresh liver. Over the course of evolution, dogs have adapted to eating liver in the wild, and excess retinol is also excreted in the urine. Vitamin A hypervitaminosis is more dangerous in cats; in dogs, it is diagnosed at extreme concentrations, which can nevertheless occur when a homemade diet is planned without sufficient care.
What can the effects be?
The effects of excess vitamin A vary depending on how long it persists and how severe it is. Initially, gastrointestinal signs such as diarrhea or reduced appetite are often observed. Neurological signs may then develop, including weakness, cognitive impairment, seizures, and even lethargy. Bone demineralization and decreased blood thyroxine levels have also been reported.
Vitamin A is essential for maintaining a dog's health and vigor. However, we must remember not to exceed the recommended doses when using supplements or feeding liver and dried liver treats. It is always best to consult a veterinarian about supplementation to ensure that we do not harm our pet.
References:
- Shastak, Y., & Pelletier, W. (2024). Pet Wellness and Vitamin A: A Narrative Overview. Animals, 14(7), 1000. https://doi.org/10.3390/ani14071000