Relationships of the carotene and vitamin A concentration in the blood, milk and feed of dairy animals
Two groups of cows were fed a ration in which three pounds of a grain mixture was used to every four pounds of hay. Two cows (Test Tube and Deborah) were fed Timothy hay with a grain mixture containing yellow corn. The other three cows (Dolly, Connie and Dot) were fed Alfalfa hay with a grain mixture containing white corn. The grain was also modified for protein balance. Relationships of carotene and Vitamin A concentrations in the blood, milk and feed were then studied.
An attempt was made to correlate the various factors involved, the variables being: period of gestation; time after calving; intake of the vitamin and its precursor in the feed; milk produced; percent of the concentration of Vitamin A activity of blood and milk represented by carotene; total Vitamin A activity of the same; and, the efficiency of the secretion in the milk of the Vitamin A activity of the feed ration.
The methods of determination of the carotene and Vitamin A (together constituting the Vitamin A activity) are given with details of the calculations.
Milk was collected on the first, third and fifth day after calving and at approximately monthly intervals thereafter. Having begun the experiment with the cows in various stages of gestation, it was possible to obtain only six samples from Dot while ten were collected from others. The blood samples also were taken monthly.
The feeds were analyzed at three monthly intervals and the rate of loss of Vitamin A activity observed. Minimum values were used in all calculations.