Question: I would like to know about the functions of vitamin A in an animal, and the appropriate time for the vitamin to be administered. I recently read an article that didn’t go into detail but simply listed its various functions – such as for maintaining the health of epithelial cells, for cell differentiation during spermatogenesis, and in the release of enzymes that digest protein, immune responses and bone growth.

Vitamin A is essential for the health of the mucus membranes that form the lining of all internal organs.

The cells of this lining produce mucus on a continuous basis, in order to keep them moist and smooth. This prevents disease-causing organisms from sticking to and growing on these membranes.

Vitamin A is produced by ruminant animals, such as cattle, sheep and goats, from the pigment found in green grass and stored in the liver. When no green grass is available the animals will use the vitamin A stored in the liver during the dry period.

This stored vitamin A in the liver only lasts for three months. The animal then needs a vitamin A supplement, because the need for this vitamin is very high during the late winter before calving and to protect against eye and lung diseases.

The best way to supplement vitamin A during late winter is by giving cattle the vitamin in injectable form and dosing small stock with a vitamin A product. This will help to prevent problems such as retained afterbirth, eye infections and pneumonia by keeping the mucus membranes of the internal organs healthy.

If it only starts to rain very late in the season and there is no green grass available for the animal to produce its own vitamin A, the treatment can be repeated after three months.

• This article was written by Dr. Danie Odendaal and first appeared in Farming SA.