Vitamin profiles of eggs as indicators of nutritional status in the laying hen: vitamin A study

Laying hens were fed deficient diets, unsupplemented or supplemented with one, two, or four times the National Research Council requirement level of vitamin A for 27 wk. Vitamin A levels of egg yolk from hens fed the unsupplemented diet slowly declined but levels of vitamin A stabilized at 12 wk in the supplemented groups and were related to dietary level. Egg production of hens fed the unsupplemented diet declined significantly after 12 wk and egg yolk levels continued to decline to Week 27. Hatchability of eggs laid by the unsupplemented hens was significantly lower at Weeks 25 and 26 than hatchability for those hens receiving dietary vitamin A. Hen weight, egg weight, and shell thickness were not consistently changed by treatment. In a second experiment, hens were fed a diet with and without 9,000 IU vitamin A/kg of diet. With birds receiving the supplemented diet, egg yolk vitamin A levels were stable after 13 wk, whereas egg yolk levels from unsupplemented hens declined slowly. Egg production with the unsupplemented diet was significantly reduced after 16 wk but the magnitude of the reduction was less than that in the first experiment, although egg vitamin A levels were as low as those in the first experiment. Hatchability of eggs during Weeks 25 to 28 was greatly reduced. Egg weight, albumen score, and chick weight were not consistently altered by vitamin A status. Because declines in egg yolk vitamin A do not precede declines in egg production they are not useful to predict future vitamin A deficiency in laying hens.