Carotene occurs in the forages consumed by cattle and is the precursor of physiological active vitamin A. The ability to convert carotene into vitamin A before it is secreted into the milk varies with different breeds.
The main site of conversion into vitamin A of ingested carotene is the intestinal wall, so that the absence of carotenoids from the tissues of these animals suggests that in them, carotenoids are either not absorbed into the circulation or are rapidly degraded in the tissues into colorless products.
The Guernsey cow (or Jersey) secretes a large proportion of vitamin A as carotene, while other breeds such as Holstein-Friesian and Ayrshire produce a milk low in carotene but equally high in vitamin A on a fat basis.
Consequently the latter milks have less color than either Jersey or Guernsey. The minimum maintenance requirement of cattle for carotene is approximately 3.5 mg per 100 kg of body weight. At least 50 to 75 percent more is needed for normal growth and maintenance of adequate plasma and liver levels.
Carotene content in cow’s milk
